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.so man.macros
.HS Tcl tcl
.BS
.SH NAME
Tcl \- overview of tool command language facilities
.BE

.SH INTRODUCTION
.PP
Tcl stands for ``tool command language'' and is pronounced ``tickle.''
It is actually two things:
a language and a library.
First, Tcl is a simple textual language,
intended primarily for issuing commands to interactive programs such
as text editors, debuggers, illustrators, and shells.  It has
a simple syntax and is also programmable, so
Tcl users can write command procedures to provide more powerful
commands than those in the built-in set.
.PP
Second, Tcl is a library package that can be embedded in application
programs.  The Tcl library consists of a parser for the Tcl
language, routines to implement the Tcl built-in commands, and
procedures that allow each application to extend Tcl with additional
commands specific to that application.  The application program
generates Tcl commands and passes them to the Tcl parser for
execution.  Commands may be generated
by reading characters from an input
source, or by associating command strings with elements of the
application's user interface, such as menu entries, buttons, or
keystrokes.
When the Tcl library receives commands it parses them
into component fields and executes built-in commands directly.
For commands implemented by the
application, Tcl calls back to the application to execute the
commands.  In many cases commands will invoke recursive invocations
of the Tcl interpreter by passing in additional strings to execute
(procedures, looping commands, and conditional commands all work
in this way).
.PP
An application program gains three advantages by using Tcl for
its command language.  First, Tcl provides a standard syntax:  once
users know Tcl, they will be able to issue commands easily
to any Tcl-based application.  Second, Tcl provides programmability.
All a Tcl application needs to do is to implement a few
application-specific low-level commands.  Tcl provides many utility
commands plus a general programming interface for building up
complex command procedures.  By using Tcl, applications need not
re-implement these features.  Third, Tcl can be used as
.VS
a common language for communicating between applications.
Inter-application communication is not built into the Tcl core
described here, but various add-on libraries, such as the Tk toolkit,
allow applications to issue commands to each other.
This makes it possible for applications to work together in much
more powerful ways than was previously possible.
.VE
.PP
This manual page focuses primarily on the Tcl language.  It describes
the language syntax and the built-in commands that will be available in
any application based on Tcl.  The individual library
procedures are described in more detail in separate manual pages, one
per procedure.

.SH "INTERPRETERS"
.PP
The central data structure in Tcl is an interpreter (C type
``Tcl_Interp'').  An interpreter consists of a set of command
bindings, a set of variable values, and a few other miscellaneous
pieces of state.  Each Tcl command is interpreted in the context
of a particular interpreter.
Some Tcl-based applications will maintain
multiple interpreters simultaneously, each associated with a
different widget or portion of the application.
Interpreters are relatively lightweight structures.  They can
be created and deleted quickly, so application programmers should feel free to
use multiple interpreters if that simplifies the application.
Eventually Tcl will provide a mechanism for sending Tcl commands
and results back and forth between interpreters, even if the
interpreters are managed by different processes.

.SH "DATA TYPES"
.PP
Tcl supports only one type of data:  strings.  All commands,
all arguments to commands, all command results, and all variable values
are strings.
Where commands require numeric arguments or return numeric results,
the arguments and results are passed as strings.
Many commands expect their string arguments to have certain formats,
but this interpretation is
up to the individual commands.  For example, arguments often contain
Tcl command strings, which may get executed as part of the commands.
The easiest way to understand the Tcl interpreter is to remember that
everything is just an operation on a string.  In many cases Tcl constructs
will look similar to more structured constructs from other languages.
However, the Tcl constructs
are not structured at all; they are just strings of characters, and this
gives them a different behavior than the structures they may look like.
.PP
Although the exact interpretation of a Tcl string depends on who is
doing the interpretation, there are three common forms that strings
take:  commands, expressions, and lists.  The major sections below
discuss these three forms in more detail.

.SH "BASIC COMMAND SYNTAX"
.PP
The Tcl language has syntactic similarities to both the Unix shells
and Lisp.  However, the interpretation of commands is different
in Tcl than in either of those other two systems.
A Tcl command string consists of one or more commands separated
by newline characters or semi-colons.
Each command consists of a collection of fields separated by
white space (spaces or tabs).
The first field must be the name of a command, and the
additional fields, if any, are arguments that will be passed to
that command.  For example, the command
.DS
\fBset a 22\fR
.DE
has three fields:  the first, \fBset\fR, is the name of a Tcl command, and
the last two, \fBa\fR and \fB22\fR, will be passed as arguments to
the \fBset\fR command.  The command name may refer either to a built-in
Tcl command, an application-specific command bound in with the library
procedure \fBTcl_CreateCommand\fR, or a command procedure defined with the
\fBproc\fR built-in command.
Arguments are passed literally as
text strings.  Individual commands may interpret those strings in any
fashion they wish.  The \fBset\fR command, for example, will treat its
first argument as the name of a variable and its second argument as a
string value to assign to that variable.  For other commands arguments
may be interpreted as integers, lists, file names, or Tcl commands.
.PP
.VS
Command names should normally be typed completely (e.g. no abbreviations).
However, if the Tcl interpreter cannot locate a command it invokes a
special command named \fBunknown\fR which attempts to find or create
the command.
For example, at many sites \fBunknown\fR will search
through library directories for the desired command and create it
as a Tcl procedure if it is found.
The \fBunknown\fR command often provides automatic completion of
abbreviated commands, but usually only for commands that were typed
interactively.
It's probably a bad idea to use abbreviations in command scripts
and other forms that will be re-used over time:  changes
to the command set may cause abbreviations to become ambiguous,
resulting in scripts that no longer work.
.VE

.SH "COMMENTS"
.PP
If the first non-blank character in a command is \fB#\fR, then everything
from the \fB#\fR up through the next newline character is treated as
a comment and ignored.  When comments are embedded inside nested
commands (e.g. fields enclosed in braces) they must have properly-matched
braces (this is necessary because when Tcl parses the top-level command
it doesn't yet know that the nested field will be used as a command so
it cannot process the nested comment character as a comment).

.SH "GROUPING ARGUMENTS WITH DOUBLE-QUOTES"
.PP
Normally each argument field ends at the next white space, but
double-quotes may be used to create arguments with embedded
space.  If an argument
field begins with a double-quote, then the argument isn't
terminated by white space (including newlines) or a semi-colon
(see below for information on semi-colons); instead it ends at the next
double-quote character.  The double-quotes are not included
in the resulting argument.  For example, the
command
.DS
\fBset a "This is a single argument"\fR
.DE
will pass two arguments to \fBset\fR:  \fBa\fR and
\fBThis is a single argument\fR.  Within double-quotes, command
substitutions, variable substitutions, and backslash substitutions
still occur, as described below.  If the first character of a
command field is not a quote, then quotes receive no special
interpretation in the parsing of that field.

.SH "GROUPING ARGUMENTS WITH BRACES"
.PP
Curly braces may also be used for grouping arguments.  They are
similar to quotes except for two differences.  First, they nest;
this makes them easier to use for complicated arguments like nested Tcl
command strings.  Second, the substitutions described below for
commands, variables, and backslashes do \fInot\fR occur in arguments
enclosed in braces, so braces can be used to prevent substitutions
where they are undesirable.
If an argument field
begins with a left brace, then the argument ends at the matching
right brace.  Tcl will strip off the outermost layer of braces
and pass the information between the braces to the command without
any further modification.  For example, in the command
.DS
\fBset a {xyz a {b c d}}\fR
.DE
the \fBset\fR command will receive two arguments: \fBa\fR
and \fBxyz a {b c d}\fR.
.PP
When braces or quotes are in effect, the matching brace
or quote need not be on
the same line as the starting quote or brace; in this case
the newline will be
included in the argument field along with any other characters up to the
matching brace or quote.  For example, the \fBeval\fR command
takes one
argument, which is a command string; \fBeval\fR invokes the Tcl
interpreter to execute the command string.  The command
.DS
\fBeval {
    set a 22
    set b 33
}\fR
.DE
will assign the value \fB22\fR to \fBa\fR and \fB33\fR to \fBb\fR.
.PP
If the first character of a command field is not a left
brace, then neither left nor right
braces in the field will be treated specially (except as part of
variable substitution; see below).

.SH "COMMAND SUBSTITUTION WITH BRACKETS"
.PP
If an open bracket occurs in a field of a command, then
command substitution occurs (except for fields enclosed in
braces).  All of the text up to the matching
close bracket is treated as a Tcl command and executed immediately.
Then the result of that command is substituted for the bracketed
text.  For example, consider the command
.DS
\fBset a [set b]\fR
.DE
When the \fBset\fR command has only a single argument, it is the
name of a variable and \fBset\fR returns the contents of that
variable.  In this case, if variable \fBb\fR has the value \fBfoo\fR,
then the command above is equivalent to the command
.DS
\fBset a foo\fR
.DE
Brackets can be used in more complex ways.  For example, if the
variable \fBb\fR has the value \fBfoo\fR and the variable \fBc\fR
has the value \fBgorp\fR, then the command
.DS
\fBset a xyz[set b].[set c]\fR
.DE
is equivalent to the command
.DS
\fBset a xyzfoo.gorp\fR
.DE
.VS
A bracketed command may contain multiple commands separated by
newlines or semi-colons in the usual fashion.
In this case the value of the last command is used for substitution.
For example, the command
.DS
\fBset a x[set b 22
expr $b+2]x\fR
.DE
is equivalent to the command
.DS
\fBset a x24x\fR
.DE
.VE
If a field is enclosed in braces then the brackets and the characters
between them are not interpreted specially; they are passed through
to the argument verbatim.

.SH "VARIABLE SUBSTITUTION WITH $"
.PP
The dollar sign (\fB$\fR) may be used as a special shorthand form
for substituting variable values.
If \fB$\fR appears in an argument that isn't enclosed in braces
then variable substitution will occur.  The characters after
the \fB$\fR, up to the first character that isn't a number, letter, or
underscore, are taken as a variable name and the string value of that
variable is substituted for the name.
.VS
For example, if variable \fBfoo\fR
has the value \fBtest\fR, then the command
.DS C
\fBset a $foo.c\fR
.DE
is equivalent to the command
.DS C
\fBset a test.c\fR
.DE
.PP
There are two special forms for variable substitution.
If the next character after the name of the variable is an
open parenthesis, then the variable is assumed to be an array
name, and all of the characters between the open parenthesis
and the next close parenthesis are taken as an index into the array.
Command substitutions and variable substitutions are
performed on the information between the parentheses before it is
used as an index.
For example, if the variable \fBx\fR is an array with one element
named \fBfirst\fR and value \fB87\fR and another element named
\fB14\fR and value \fBmore\fR, then the command
.DS C
\fBset a xyz$x(first)zyx
.DE
is equivalent to the command
.DS C
\fBset a xyz87zyx\fR
.DE
If the variable \fBindex\fR has the value \fB14\fR, then the command
.DS C
\fBset a xyz$x($index)zyx
.DE
is equivalent to the command
.DS C
\fBset a xyzmorezyx
.DE
For more information on arrays, see VARIABLES AND ARRAYS below.
.PP
The second special form for variables occurs when
the dollar sign is followed by an open curly brace.
In this case the variable name consists of all the characters
up to the next curly brace.
Array references are not possible in this form:  the name
between braces is assumed to refer to a scalar variable.
For example, if variable \fBfoo\fR has the value \fBtest\fR,
then the command
.DS C
\fBset a abc${foo}bar\fR
.DE
is equivalent to the command
.DS C
\fBset a abctestbar\fR
.DE
.VE
Variable substitution does not occur in arguments that are enclosed
in braces:  the
dollar sign and variable name are passed through to the argument verbatim.
.PP
The dollar sign abbreviation is simply a shorthand form.  \fB$a\fR is
completely equivalent to \fB[set a]\fR; it is provided as a convenience
to reduce typing.

.SH "SEPARATING COMMANDS WITH SEMI-COLONS"
.PP
Normally, each command occupies one line (the command is terminated by
a newline character).  However, semi-colon (``;'') is treated
as a command separator character; multiple commands may be placed
on one line by separating them with a semi-colon.  Semi-colons are
not treated as command separators if they appear within curly braces
or double-quotes.

.SH "BACKSLASH SUBSTITUTION"
.PP
Backslashes may be used to insert non-printing characters into
command fields and also to insert special characters like
braces and brackets into fields
without them being interpreted specially as described above.
The backslash sequences understood by the Tcl interpreter are
listed below.  In each case, the backslash
sequence is replaced by the given character:
.TP 20
\fB\eb\fR
Backspace (0x8).
.TP 20
\fB\ef\fR
Form feed (0xc).
.TP 20
\fB\en\fR
Newline (0xa).
.TP 20
\fB\er\fR
Carriage-return (0xd).
.TP 20
\fB\et\fR
Tab (0x9).
.TP 20
\fB\ev\fR
Vertical tab (0xb).
.TP 20
\fB\e{\fR
Left brace (``{'').
.TP 20
\fB\e}\fR
Right brace (``}'').
.TP 20
\fB\e[\fR
Open bracket (``['').
.TP 20
\fB\e]\fR
Close bracket (``]'').
.TP 20
\fB\e$\fR
Dollar sign (``$'').
.TP 20
\fB\e<space>\fR
Space (`` ''): doesn't terminate argument.
.br
.TP 20
\fB\e;\fR
Semi-colon: doesn't terminate command.
.TP 20
\fB\e"\fR
Double-quote.
.TP 20
\fB\e<newline>\fR
Nothing:  this joins two lines together
into a single line.  This backslash feature is unique in that
it will be applied even when the sequence occurs within braces.
.TP 20
\fB\e\e\fR
Backslash (``\e'').
.TP 20
\fB\e\fIddd\fR
The digits \fIddd\fR (one, two, or three of them) give the octal value of
the character.  Null characters may not be embedded in command fields;
if \fIddd\fR is zero then the backslash sequence is ignored (i.e. it
maps to an empty string).
.PP
For example, in the command
.DS
\fBset a \e{x\e[\e\0yz\e141\fR
.DE
the second argument to \fBset\fR will be ``\fB{x[\0yza\fR''.
.PP
If a backslash is followed by something other than one of the options
described above, then the backslash is transmitted to the argument
field without any special processing, and the Tcl scanner continues
normal processing with the next character.  For example, in the
command
.DS
\fBset \e*a \e\e\e{foo\fR
.DE
The first argument to \fBset\fR will be \fB\e*a\fR and the second
argument will be \fB\e{foo\fR.
.PP
If an argument is enclosed in braces, then backslash sequences inside
the argument are parsed but no substitution occurs (except for
backslash-newline):  the backslash
sequence is passed through to the argument as is, without making
any special interpretation of the characters in the backslash sequence.
In particular, backslashed braces are not counted in locating the
matching right brace that terminates the argument.
For example, in the
command
.DS
\fBset a {\e{abc}\fR
.DE
the second argument to \fBset\fR will be \fB\e{abc\fR.
.PP
This backslash mechanism is not sufficient to generate absolutely
any argument structure; it only covers the
most common cases.  To produce particularly complicated arguments
it is probably easiest to use the \fBformat\fR command along with
command substitution.

.SH "COMMAND SUMMARY"
.IP [1]
A command is just a string.
.IP [2]
Within a string commands are separated by newlines or semi-colons
(unless the newline or semi-colon is within braces or brackets
or is backslashed).
.IP [3]
A command consists of fields.  The first field is the name of the command.
The other fields are strings that are passed to that command as arguments.
.IP [4]
Fields are normally separated by white space.
.IP [5]
Double-quotes allow white space and semi-colons to appear within
a single argument.
Command substitution, variable substitution, and backslash substitution
still occur inside quotes.
.IP [6]
Braces defer interpretation of special characters.
If a field begins with a left brace, then it consists of everything
between the left brace and the matching right brace. The
braces themselves are not included in the argument.
No further processing is done on the information between the braces
except that backslash-newline sequences are eliminated.
.IP [7]
If a field doesn't begin with a brace then backslash,
variable, and command substitution are done on the field.  Only a
single level of processing is done:  the results of one substitution
are not scanned again for further substitutions or any other
special treatment.  Substitution can
occur on any field of a command, including the command name
as well as the arguments.
.IP [8]
If the first non-blank character of a command is a \fB#\fR, everything
from the \fB#\fR up through the next newline is treated as a comment
and ignored.

.SH "EXPRESSIONS"
.VS
.PP
The second major interpretation applied to strings in Tcl is
as expressions.  Several commands, such as \fBexpr\fR, \fBfor\fR,
and \fBif\fR, treat one or more of their arguments as expressions
and call the Tcl expression processors (\fBTcl_ExprLong\fR,
\fBTcl_ExprBoolean\fR, etc.) to evaluate them.
The operators permitted in Tcl expressions are a subset of
the operators permitted in C expressions, and they have the
same meaning and precedence as the corresponding C operators.
Expressions almost always yield numeric results
(integer or floating-point values).
For example, the expression
.DS
\fB8.2 + 6\fR
.DE
evaluates to 14.2.
Tcl expressions differ from C expressions in the way that
operands are specified, and in that Tcl expressions support
non-numeric operands and string comparisons.
.PP
A Tcl expression consists of a combination of operands, operators,
and parentheses.
White space may be used between the operands and operators and
parentheses; it is ignored by the expression processor.
Where possible, operands are interpreted as integer values.
Integer values may be specified in decimal (the normal case), in octal (if the
first character of the operand is \fB0\fR), or in hexadecimal (if the first
two characters of the operand are \fB0x\fR).
If an operand does not have one of the integer formats given
above, then it is treated as a floating-point number if that is
possible.  Floating-point numbers may be specified in any of the
ways accepted by an ANSI-compliant C compiler (except that the
``f'', ``F'', ``l'', and ``L'' suffixes will not be permitted in
most installations).  For example, all of the
following are valid floating-point numbers:  2.1, 3., 6e4, 7.91e+16.
If no numeric interpretation is possible, then an operand is left
as a string (and only a limited set of operators may be applied to
it).
.PP
Operands may be specified in any of the following ways:
.IP [1]
As an numeric value, either integer or floating-point.
.IP [2]
As a Tcl variable, using standard \fB$\fR notation.
The variable's value will be used as the operand.
.IP [3]
As a string enclosed in double-quotes.
The expression parser will perform backslash, variable, and
command substitutions on the information between the quotes,
and use the resulting value as the operand
.IP [4]
As a string enclosed in braces.
The characters between the open brace and matching close brace
will be used as the operand without any substitutions.
.IP [5]
As a Tcl command enclosed in brackets.
The command will be executed and its result will be used as
the operand.
.LP
Where substitutions occur above (e.g. inside quoted strings), they
are performed by the expression processor.
However, an additional layer of substitution may already have
been performed by the command parser before the expression
processor was called.
As discussed below, it is usually best to enclose expressions
in braces to prevent the command parser from performing substitutions
on the contents.
.PP
For some examples of simple expressions, suppose the variable
\fBa\fR has the value 3 and
the variable \fBb\fR has the value 6.
Then the expression on the left side of each of the lines below
will evaluate to the value on the right side of the line:
.DS
.ta 6c
\fB3.1 + $a    6.1
2 + "$a.$b"    5.6
4*[llength "6 2"]    8
{word one} < "word $a"    0\fR
.DE
.PP
The valid operators are listed below, grouped in decreasing order
of precedence:
.TP 20
\fB\-\0\0~\0\0!\fR
Unary minus, bit-wise NOT, logical NOT.  None of these operands
may be applied to string operands, and bit-wise NOT may be
applied only to integers.
.TP 20
\fB*\0\0/\0\0%\fR
Multiply, divide, remainder.  None of these operands may be
applied to string operands, and remainder may be applied only
to integers.
.TP 20
\fB+\0\0\-\fR
Add and subtract.  Valid for any numeric operands.
.TP 20
\fB<<\0\0>>\fR
Left and right shift.  Valid for integer operands only.
.TP 20
\fB<\0\0>\0\0<=\0\0>=\fR
Boolean less, greater, less than or equal, and greater than or equal.
Each operator produces 1 if the condition is true, 0 otherwise.
These operators may be applied to strings as well as numeric operands,
in which case string comparison is used.
.TP 20
\fB==\0\0!=\fR
Boolean equal and not equal.  Each operator produces a zero/one result.
Valid for all operand types.
.TP 20
\fB&\fR
Bit-wise AND.  Valid for integer operands only.
.TP 20
\fB^\fR
Bit-wise exclusive OR.  Valid for integer operands only.
.TP 20
\fB|\fR
Bit-wise OR.  Valid for integer operands only.
.TP 20
\fB&&\fR
Logical AND.  Produces a 1 result if both operands are non-zero, 0 otherwise.
Valid for numeric operands only (integers or floating-point).
.TP 20
\fB||\fR
Logical OR.  Produces a 0 result if both operands are zero, 1 otherwise.
Valid for numeric operands only (integers or floating-point).
.TP 20
\fIx\fB?\fIy\fB:\fIz\fR
If-then-else, as in C.  If \fIx\fR
evaluates to non-zero, then the result is the value of \fIy\fR.
Otherwise the result is the value of \fIz\fR.
The \fIx\fR operand must have a numeric value.
.LP
See the C manual for more details on the results
produced by each operator.
All of the binary operators group left-to-right within the same
precedence level.  For example, the expression
.DS
\fB4*2 < 7\fR
.DE
evaluates to 0.
.PP
The \fB&&\fP, \fB||\fP, and \fB?:\fP operators have ``lazy
evaluation'', just as in C,
which means that operands are not evaluated if they are
not needed to determine the outcome.  For example, in
.DS
\fB$v ? [a] : [b]\fR
.DE
only one of \fB[a]\fR or \fB[b]\fR will actually be evaluated,
depending on the value of \fB$v\fP.
.PP
All internal computations involving integers are done with the C type
\fIlong\fP, and all internal computations involving floating-point are
done with the C type \fIdouble\fP.
When converting a string to floating-point, exponent overflow is
detected and results in a Tcl error.
For conversion to integer from string, detection of overflow depends
on the behavior of some routines in the local C library, so it should
be regarded as unreliable.
In any case, overflow and underflow are generally not detected
reliably for intermediate results.
.PP
Conversion among internal representations for integer, floating-point,
and string operands is done automatically as needed.
For arithmetic computations, integers are used until some
floating-point number is introduced, after which floating-point is used.
For example,
.DS
\fB5 / 4\fR
.DE
yields the result 1, while
.DS
\fB5 / 4.0\fR
\fB5 / ( [string length "abcd"] + 0.0 )
.DE
both yield the result 1.25.
.PP
String values may be used as operands of the comparison operators,
although the expression evaluator tries to do comparisons as integer
or floating-point when it can.
If one of the operands of a comparison is a string and the other
has a numeric value, the numeric operand is converted back to
a string using the C \fIsprintf\fP format specifier
\fB%d\fR for integers and \fB%g\fR for floating-point values.
For example, the expressions
.DS
\fB"0x03" > "2"\fR
\fB"0y" < "0x12"\fR
.DE
both evaluate to 1.  The first comparison is done using integer
comparison, and the second is done using string comparison after
the second operand is converted to the string ``18''.
.VE
.PP
In general it is safest to enclose an expression in braces when
entering it in a command:  otherwise, if the expression contains
any white space then the Tcl interpreter will split it
among several arguments.  For example, the command
.DS C
\fBexpr $a + $b\fR
.DE
results in three arguments being passed to \fBexpr\fR:  \fB$a\fR,
\fB+\fR, and \fB$b\fR.  In addition, if the expression isn't in braces
then the Tcl interpreter will perform variable and command substitution
immediately (it will happen in the command parser rather than in
the expression parser).  In many cases the expression is being
passed to a command that will evaluate the expression later (or
even many times if, for example, the expression is to be used to
decide when to exit a loop).  Usually the desired goal is to re-do
the variable or command substitutions each time the expression is
evaluated, rather than once and for all at the beginning.  For example,
the command
.DS C
.ta 7c
\fBfor {set i 1} $i<=10 {incr i} {...}\fR    *** WRONG ***
.DE
is probably intended to iterate over all values of \fBi\fR from 1 to 10.
After each iteration of the body of the loop, \fBfor\fR will pass
its second argument to the expression evaluator to see whether or not
to continue processing.  Unfortunately, in this case the value of \fBi\fR
in the second argument will be substituted once and for all when the
\fBfor\fR command is parsed.  If \fBi\fR was 0 before the \fBfor\fR
command was invoked then \fBfor\fR's second argument will be \fB0<=10\fR
which will always evaluate to 1, even though \fBi\fR's value eventually
becomes greater than 10.  In the above case the loop will never
terminate.  Instead, the expression should be placed in braces:
.DS C
.ta 7c
\fBfor {set i 1} {$i<=10} {incr i} {...}\fR    *** RIGHT ***
.DE
This causes the substitution of \fBi\fR's
value to be delayed; it will be re-done each time the expression is
evaluated, which is the desired result.

.SH LISTS
.PP
The third major way that strings are interpreted in Tcl is as lists.
A list is just a string with a list-like structure
consisting of fields separated by white space.  For example, the
string
.DS
\fBAl Sue Anne John\fR
.DE
is a list with four elements or fields.
Lists have the same basic structure as command strings, except
that a newline character in a list is treated as a field separator
just like space or tab.  Conventions for braces and quotes
and backslashes are the same for lists as for commands.  For example,
the string
.DS
\fBa b\e c {d e {f g h}}\fR
.DE
is a list with three elements:  \fBa\fR, \fBb c\fR, and \fBd e {f g h}\fR.
Whenever an element
is extracted from a list, the same rules about braces and quotes and
backslashes are applied as for commands.  Thus in the example above
when the third element is extracted from the list, the result is
.DS
\fBd e {f g h}\fR
.DE
(when the field was extracted, all that happened was to strip off
the outermost layer of braces).  Command substitution and
variable substitution are never
made on a list (at least, not by the list-processing commands; the
list can always be passed to the Tcl interpreter for evaluation).
.PP
The Tcl commands \fBconcat\fR, \fBforeach\fR,
.VS
\fBlappend\fR, \fBlindex\fR, \fBlinsert\fR, \fBlist\fR, \fBllength\fR,
\fBlrange\fR, \fBlreplace\fR, \fBlsearch\fR, and \fBlsort\fR allow
you to build lists,
.VE
extract elements from them, search them, and perform other list-related
functions.

.SH "REGULAR EXPRESSIONS"
.VS
.PP
Tcl provides two commands that support string matching using
\fBegrep\fR-style regular expressions: \fBregexp\fR and \fBregsub\fR.
Regular expressions are implemented using Henry Spencer's package,
and the description of regular expressions below is copied verbatim
from his manual entry.
.PP
A regular expression is zero or more \fIbranches\fR, separated by ``|''.
It matches anything that matches one of the branches.
.PP
A branch is zero or more \fIpieces\fR, concatenated.
It matches a match for the first, followed by a match for the second, etc.
.PP
A piece is an \fIatom\fR possibly followed by ``*'', ``+'', or ``?''.
An atom followed by ``*'' matches a sequence of 0 or more matches of the atom.
An atom followed by ``+'' matches a sequence of 1 or more matches of the atom.
An atom followed by ``?'' matches a match of the atom, or the null string.
.PP
An atom is a regular expression in parentheses (matching a match for the
regular expression), a \fIrange\fR (see below), ``.''
(matching any single character), ``^'' (matching the null string at the
beginning of the input string), ``$'' (matching the null string at the
end of the input string), a ``\e'' followed by a single character (matching
that character), or a single character with no other significance
(matching that character).
.PP
A \fIrange\fR is a sequence of characters enclosed in ``[]''.
It normally matches any single character from the sequence.
If the sequence begins with ``^'',
it matches any single character \fInot\fR from the rest of the sequence.
If two characters in the sequence are separated by ``\-'', this is shorthand
for the full list of ASCII characters between them
(e.g. ``[0-9]'' matches any decimal digit).
To include a literal ``]'' in the sequence, make it the first character
(following a possible ``^'').
To include a literal ``\-'', make it the first or last character.
.PP
If a regular expression could match two different parts of a string,
it will match the one which begins earliest.
If both begin in the same place but match different lengths, or match
the same length in different ways, life gets messier, as follows.
.PP
In general, the possibilities in a list of branches are considered in
left-to-right order, the possibilities for ``*'', ``+'', and ``?'' are
considered longest-first, nested constructs are considered from the
outermost in, and concatenated constructs are considered leftmost-first.
The match that will be chosen is the one that uses the earliest
possibility in the first choice that has to be made.
If there is more than one choice, the next will be made in the same manner
(earliest possibility) subject to the decision on the first choice.
And so forth.
.PP
For example, ``(ab|a)b*c'' could match ``abc'' in one of two ways.
The first choice is between ``ab'' and ``a''; since ``ab'' is earlier, and does
lead to a successful overall match, it is chosen.
Since the ``b'' is already spoken for,
the ``b*'' must match its last possibility\(emthe empty string\(emsince
it must respect the earlier choice.
.PP
In the particular case where no ``|''s are present and there is only one
``*'', ``+'', or ``?'', the net effect is that the longest possible
match will be chosen.
So ``ab*'', presented with ``xabbbby'', will match ``abbbb''.
Note that if ``ab*'' is tried against ``xabyabbbz'', it
will match ``ab'' just after ``x'', due to the begins-earliest rule.
(In effect, the decision on where to start the match is the first choice
to be made, hence subsequent choices must respect it even if this leads them
to less-preferred alternatives.)
.VE

.SH "COMMAND RESULTS"
.PP
Each command produces two results:  a code and a string.  The
code indicates whether the command completed successfully or not,
and the string gives additional information.  The valid codes are
defined in tcl.h, and are:
.RS
.TP 20
\fBTCL_OK\fR
This is the normal return code, and indicates that the command completed
successfully.  The string gives the command's return value.
.TP 20
\fBTCL_ERROR\fR
Indicates that an error occurred; the string gives a message describing
the error.
.VS
In addition, the global variable \fBerrorInfo\fR will contain
human-readable information
describing which commands and procedures were being executed when the
error occurred, and the global variable \fBerrorCode\fR will contain
machine-readable details about the error, if they are available.
See the section BUILT-IN VARIABLES below for more information.
.VE
.VE
.TP 20
\fBTCL_RETURN\fR
Indicates that the \fBreturn\fR command has been invoked, and that the
current procedure (or top-level command or \fBsource\fR command)
should return immediately.  The
string gives the return value for the procedure or command.
.TP 20
\fBTCL_BREAK\fR
Indicates that the \fBbreak\fR command has been invoked, so the
innermost loop should abort immediately.  The string should always
be empty.
.TP 20
\fBTCL_CONTINUE\fR
Indicates that the \fBcontinue\fR command has been invoked, so the
innermost loop should go on to the next iteration.  The string
should always be empty.
.RE
Tcl programmers do not normally need to think about return codes,
since TCL_OK is almost always returned.  If anything else is returned
by a command, then the Tcl interpreter immediately stops processing
commands and returns to its caller.  If there are several nested
invocations of the Tcl interpreter in progress, then each nested
command will usually return the error to its caller, until eventually
the error is reported to the top-level application code.  The
application will then display the error message for the user.
.PP
In a few cases, some commands will handle certain ``error'' conditions
themselves and not return them upwards.  For example, the \fBfor\fR
command checks for the TCL_BREAK code; if it occurs, then \fBfor\fR
stops executing the body of the loop and returns TCL_OK to its
caller.  The \fBfor\fR command also handles TCL_CONTINUE codes and the
procedure interpreter handles TCL_RETURN codes.  The \fBcatch\fR
command allows Tcl programs to catch errors and handle them without
aborting command interpretation any further.

.SH PROCEDURES
.PP
Tcl allows you to extend the command interface by defining
procedures.  A Tcl procedure can be invoked just like any other Tcl
command (it has a name and it receives one or more arguments).
The only difference is that its body isn't a piece of C code linked
into the program; it is a string containing one or more other
Tcl commands.  See the \fBproc\fR command for information on
how to define procedures and what happens when they are invoked.

.SH VARIABLES \- SCALARS AND ARRAYS
.VS
.PP
Tcl allows the definition of variables and the use of their values
either through \fB$\fR-style variable substitution, the \fBset\fR
command, or a few other mechanisms.
Variables need not be declared:  a new variable will automatically
be created each time a new variable name is used.
.PP
Tcl supports two types of variables:  scalars and arrays.
A scalar variable has a single value, whereas an array variable
can have any number of elements, each with a name (called
its ``index'') and a value.
Array indexes may be arbitrary strings; they need not be numeric.
Parentheses are used refer to array elements in Tcl commands.
For example, the command
.DS C
\fBset x(first) 44\fR
.DE
will modify the element of \fBx\fR whose index is \fBfirst\fR
so that its new value is \fB44\fR.
Two-dimensional arrays can be simulated in Tcl by using indexes
that contain multiple concatenated values.
For example, the commands
.DS C
\fBset a(2,3) 1\fR
\fBset a(3,6) 2\fR
.DE
set the elements of \fBa\fR whose indexes are \fB2,3\fR and \fB3,6\fR.
.PP
In general, array elements may be used anywhere in Tcl that scalar
variables may be used.
If an array is defined with a particular name, then there may
not be a scalar variable with the same name.
Similarly, if there is a scalar variable with a particular
name then it is not possible to make array references to the
variable.
To convert a scalar variable to an array or vice versa, remove
the existing variable with the \fBunset\fR command.
.PP
The \fBarray\fR command provides several features for dealing
with arrays, such as querying the names of all the elements of
the array and searching through the array one element at a time.
.VE
.PP
Variables may be either global or local.  If a variable
name is used when a procedure isn't being executed, then it
automatically refers to a global variable.  Variable names used
within a procedure normally refer to local variables associated with that
invocation of the procedure.  Local variables are deleted whenever
a procedure exits.  The \fBglobal\fR command may be used to request
that a name refer to a global variable for the duration of the current
procedure (this is somewhat analogous to \fBextern\fR in C).

.SH "BUILT-IN COMMANDS"
.PP
The Tcl library provides the following built-in commands, which will
be available in any application using Tcl.  In addition to these
built-in commands, there may be additional commands defined by each
application, plus commands defined as Tcl procedures.
In the command syntax descriptions below, words in boldface are
literals that you type verbatim to Tcl.
Words in italics are meta-symbols; they serve as names for any of
a range of values that you can type.
Optional arguments or groups of arguments are indicated by enclosing them
in question-marks.
Ellipses (``...'') indicate that any number of additional
arguments or groups of arguments may appear, in the same format
as the preceding argument(s).
.TP
\fBappend \fIvarName value \fR?\fIvalue value ...\fR?
.VS
Append all of the \fIvalue\fR arguments to the current value
of variable \fIvarName\fR.  If \fIvarName\fR doesn't exist,
it is given a value equal to the concatenation of all the
\fIvalue\fR arguments.
This command provides an efficient way to build up long
variables incrementally.
For example, ``\fBappend a $b\fR'' is much more efficient than
``\fBset a $a$b\fR'' if \fB$a\fR is long.
.VE
.TP
\fBarray \fIoption arrayName\fR ?\fIarg arg ...\fR?
.VS
This command performs one of several operations on the
variable given by \fIarrayName\fR.
\fIArrayName\fR must be the name of an existing array variable.
The \fIoption\fR argument determines what action is carried
out by the command.
The legal \fIoptions\fR (which may be abbreviated) are:
.RS
.TP
\fBarray anymore \fIarrayName searchId\fR
Returns 1 if there are any more elements left to be processed
in an array search, 0 if all elements have already been
returned.
\fISearchId\fR indicates which search on \fIarrayName\fR to
check, and must have been the return value from a previous
invocation of \fBarray startsearch\fR.
This option is particularly useful if an array has an element
with an empty name, since the return value from
\fBarray nextelement\fR won't indicate whether the search
has been completed.
.TP
\fBarray donesearch \fIarrayName searchId\fR
This command terminates an array search and destroys all the
state associated with that search.  \fISearchId\fR indicates
which search on \fIarrayName\fR to destroy, and must have
been the return value from a previous invocation of
\fBarray startsearch\fR.  Returns an empty string.
.TP
\fBarray names \fIarrayName\fR
Returns a list containing the names of all of the elements in
the array.
If there are no elements in the array then an empty string is
returned.
.TP
\fBarray nextelement \fIarrayName searchId\fR
Returns the name of the next element in \fIarrayName\fR, or
an empty string if all elements of \fIarrayName\fR have
already been returned in this search.  The \fIsearchId\fR
argument identifies the search, and must have
been the return value of an \fBarray startsearch\fR command.
Warning:  if elements are added to or deleted from the array,
then all searches are automatically terminated just as if
\fBarray donesearch\fR had been invoked; this will cause
\fBarray nextelement\fR operations to fail for those searches.
.TP
\fBarray size \fIarrayName\fR
Returns a decimal string giving the number of elements in the
array.
.TP
\fBarray startsearch \fIarrayName\fR
This command initializes an element-by-element search through the
array given by \fIarrayName\fR, such that invocations of the
\fBarray nextelement\fR command will return the names of the
individual elements in the array.
When the search has been completed, the \fBarray donesearch\fR
command should be invoked.
The return value is a
search identifier that must be used in \fBarray nextelement\fR
and \fBarray donesearch\fR commands; it allows multiple
searches to be underway simultaneously for the same array.
.VE
.RE
.TP
\fBbreak\fR
This command may be invoked only inside the body of a loop command
such as \fBfor\fR or \fBforeach\fR or \fBwhile\fR.  It returns a TCL_BREAK code
to signal the innermost containing loop command to return immediately.
.TP
\fBcase\fI string \fR?\fBin\fR? \fIpatList body \fR?\fIpatList body \fR...?
.TP
\fBcase\fI string \fR?\fBin\fR? {\fIpatList body \fR?\fIpatList body \fR...?}
Match \fIstring\fR against each of the \fIpatList\fR arguments
in order.  If one matches, then evaluate the following \fIbody\fR argument
by passing it recursively to the Tcl interpreter, and return the result
of that evaluation.  Each \fIpatList\fR argument consists of a single
pattern or list of patterns.  Each pattern may contain any of the wild-cards
described under \fBstring match\fR.  If a \fIpatList\fR
argument is \fBdefault\fR, the corresponding body will be evaluated
if no \fIpatList\fR matches \fIstring\fR.  If no \fIpatList\fR argument
matches \fIstring\fR and no default is given, then the \fBcase\fR
command returns an empty string.
.RS
.PP
Two syntaxes are provided.
The first uses a separate argument for each of the patterns and commands;
this form is convenient if substitutions are desired on some of the
patterns or commands.
.VS
The second form places all of the patterns and commands together into
a single argument; the argument must have proper list structure, with
the elements of the list being the patterns and commands.
The second form makes it easy to construct multi-line case commands,
since the braces around the whole list make it unnecessary to include a
backslash at the end of each line.
Since the \fIpatList\fR arguments are in braces in the second form,
no command or variable substitutions are performed on them;  this makes
the behavior of the second form different than the first form in some
cases.
.PP
Below are some examples of \fBcase\fR commands:
.DS
\fBcase abc in {a b} {format 1} default {format 2} a* {format 3}
.DE
will return \fB3\fR,
.DS
.ta .5c 1c
\fBcase a in {
    {a b} {format 1}
    default {format 2}
    a* {format 3}
}
.DE
will return \fB1\fR, and
.DS
.ta .5c 1c
\fBcase xyz {
    {a b}
        {format 1}
    default
        {format 2}
    a*
        {format 3}
}
.DE
will return \fB2\fR.
.VE
.RE
.TP
\fBcatch\fI command \fR?\fIvarName\fR?
The \fBcatch\fR command may be used to prevent errors from aborting
command interpretation.  \fBCatch\fR calls the Tcl interpreter recursively
to execute \fIcommand\fR, and always returns a TCL_OK code, regardless of
any errors that might occur while executing \fIcommand\fR.  The return
value from \fBcatch\fR is a decimal string giving the
code returned by the Tcl interpreter after executing \fIcommand\fR.
This will be \fB0\fR (TCL_OK) if there were no errors in \fIcommand\fR; otherwise
it will have a non-zero value corresponding to one of the exceptional
return codes (see tcl.h for the definitions of code values).  If the
\fIvarName\fR argument is given, then it gives the name of a variable;
\fBcatch\fR will set the value of the variable to the string returned
from \fIcommand\fR (either a result or an error message).
.TP
\fBcd \fR?\fIdirName\fR?
.VS
Change the current working directory to \fIdirName\fR, or to the
home directory (as specified in the HOME environment variable) if
\fIdirName\fR is not given.
If \fIdirName\fR starts with a tilde, then tilde-expansion is
done as described for \fBTcl_TildeSubst\fR.
Returns an empty string.
This command can potentially be disruptive to an application,
so it may be removed in some applications.
.TP
\fBclose \fIfileId\fR
Closes the file given by \fIfileId\fR.
\fIFileId\fR must be the return value from a previous invocation
of the \fBopen\fR command; after this command, it should not be
used anymore.
If \fIfileId\fR refers to a command pipeline instead of a file,
then \fBclose\fR waits for the children to complete.
The normal result of this command is an empty string, but errors
are returned if there are problems in closing the file or waiting
for children to complete.
.VE
.TP
\fBconcat\fI arg \fR?\fIarg ...\fR?
This command treats each argument as a list and concatenates them
into a single list.  It permits any number of arguments.  For example,
the command
.RS
.DS
\fBconcat a b {c d e} {f {g h}}\fR
.DE
will return
.DS
\fBa b c d e f {g h}\fR
.DE
as its result.
.RE
.TP
\fBcontinue\fR
This command may be invoked only inside the body of a loop command
such as \fBfor\fR or \fBforeach\fR or \fBwhile\fR.  It
returns a  TCL_CONTINUE code
to signal the innermost containing loop command to skip the
remainder of the loop's body
but continue with the next iteration of the loop.
.TP
\fBeof \fIfileId\fR
.VS
Returns 1 if an end-of-file condition has occurred on \fIfileId\fR,
0 otherwise.
\fIFileId\fR must have been the return
value from a previous call to \fBopen\fR, or it may be \fBstdin\fR,
\fBstdout\fR, or \fBstderr\fR to refer to one of the standard I/O
channels.
.VE
.TP
\fBerror \fImessage\fR ?\fIinfo\fR? ?\fIcode\fR?
Returns a TCL_ERROR code, which causes command interpretation to be
unwound.  \fIMessage\fR is a string that is returned to the application
to indicate what went wrong.
.RS
.PP
If the \fIinfo\fR argument is provided and is non-empty,
it is used to initialize the global variable \fBerrorInfo\fR.
\fBerrorInfo\fR is used to accumulate a stack trace of what
was in progress when an error occurred; as nested commands unwind,
the Tcl interpreter adds information to \fBerrorInfo\fR.  If the
\fIinfo\fR argument is present, it is used to initialize
\fBerrorInfo\fR and the first increment of unwind information
will not be added by the Tcl interpreter.  In other
words, the command containing the \fBerror\fR command will not appear
in \fBerrorInfo\fR; in its place will be \fIinfo\fR.
This feature is most useful in conjunction with the \fBcatch\fR command:
if a caught error cannot be handled successfully, \fIinfo\fR can be used
to return a stack trace reflecting the original point of occurrence
of the error:
.DS
\fBcatch {...} errMsg
set savedInfo $errorInfo
\&...
error $errMsg $savedInfo\fR
.DE
.PP
.VS
If the \fIcode\fR argument is present, then its value is stored
in the \fBerrorCode\fR global variable.  This variable is intended
to hold a machine-readable description of the error in cases where
such information is available; see the section BUILT-IN VARIABLES
below for information on the proper format for the variable.
If the \fIcode\fR argument is not
present, then \fBerrorCode\fR is automatically reset to
``NONE'' by the Tcl interpreter as part of processing the
error generated by the command.
.VE
.RE
.TP
\fBeval \fIarg \fR?\fIarg ...\fR?
\fBEval\fR takes one or more arguments, which together comprise a Tcl
command (or collection of Tcl commands separated by newlines in the
usual way).  \fBEval\fR concatenates all its arguments in the same
fashion as the \fBconcat\fR command, passes the concatenated string to the
Tcl interpreter recursively, and returns the result of that
evaluation (or any error generated by it).
.TP
\fBexec \fIarg \fR?\fIarg ...\fR?
.VS
This command treats its arguments as the specification
of one or more UNIX commands to execute as subprocesses.
The commands take the form of a standard shell pipeline;
``|'' arguments separate commands in the
pipeline and cause standard output of the preceding command
to be piped into standard input of the next command.
.RS
.PP
Under normal conditions the result of the \fBexec\fR command
consists of the standard output produced by the last command
in the pipeline.
If any of the commands in the pipeline exit abnormally or
are killed or suspended, then \fBexec\fR will return an error
and the error message will include the pipeline's output followed by
error messages describing the abnormal terminations; the
\fBerrorCode\fR variable will contain additional information
about the last abnormal termination encountered.
If any of the commands writes to its standard error file,
then \fBexec\fR will return an error, and the error message
will include the pipeline's output, followed by messages
about abnormal terminations (if any), followed by the standard error
output.
.PP
If the last character of the result or error message
is a newline then that character is deleted from the result
or error message for consistency with normal
Tcl return values.
.PP
If an \fIarg\fR has the value ``>'' then the
following argument is taken as the name of a file and
the standard output of the last command in the pipeline
is redirected to the file.  In this situation \fBexec\fR
will normally return an empty string.
.PP
If an \fIarg\fR has the value ``<'' then the following
argument is taken as the name of a file to use
for standard input to the first command in the
pipeline.
If an argument has the value ``<<'' then the following
argument is taken as an immediate value to be passed to
the first command as standard input.
If there is no ``<'' or ``<<'' argument then the standard
input for the first command in the pipeline is taken from
the application's current standard input.
.PP
If the last \fIarg\fR is ``&'' then the command will be
executed in background.
In this case the standard output from the last command
in the pipeline will
go to the application's standard output unless
redirected in the command, and error output from all
the commands in the pipeline will go to the application's
standard error file.
.PP
Each \fIarg\fR becomes one word for a command, except for
``|'', ``<'', ``<<'', ``>'', and ``&'' arguments, and the
arguments that follow ``<'', ``<<'', and ``>''.
The first word in each command is taken as the command name;
tilde-substitution is performed on it, and the directories
in the PATH environment variable are searched for
an executable by the given name.
No ``glob'' expansion or other shell-like substitutions
are performed on the arguments to commands.
.RE
.TP
\fBexit \fR?returnCode\fR?
Terminate the process, returning \fIreturnCode\fR to the
parent as the exit status.
If \fIreturnCode\fR isn't specified then it defaults
to 0.
.VE
.TP
\fBexpr \fIarg\fR
Calls the expression processor to evaluate \fIarg\fR, and returns
the result as a string.  See the section EXPRESSIONS above.
.TP
\fBfile \fIoption\fR \fIname\fR ?\fIarg arg ...\fR?
.VS
Operate on a file or a file name.  \fIName\fR is the name of a file;
if it starts with a tilde, then tilde substitution is done before
executing the command (see the manual entry for \fBTcl_TildeSubst\fR
for details).
\fIOption\fR indicates what to do with the file name.  Any unique
abbreviation for \fIoption\fR is acceptable.  The valid options are:
.RS
.TP
\fBfile \fBatime \fIname\fR
Return a decimal string giving the time at which file \fIname\fR
was last accessed.  The time is measured in the standard UNIX
fashion as seconds from a fixed starting time (often January 1, 1970).
If the file doesn't exist or its access time cannot be queried then an
error is generated.
.TP
\fBfile \fBdirname \fIname\fR
Return all of the characters in \fIname\fR up to but not including
the last slash character.  If there are no slashes in \fIname\fR
then return ``.''.  If the last slash in \fIname\fR is its first
character, then return ``/''.
.TP
\fBfile \fBexecutable \fIname\fR
Return \fB1\fR if file \fIname\fR is executable by
the current user, \fB0\fR otherwise.
.TP
\fBfile \fBexists \fIname\fR
Return \fB1\fR if file \fIname\fR exists and the current user has
search privileges for the directories leading to it, \fB0\fR otherwise.
.TP
\fBfile \fBextension \fIname\fR
Return all of the characters in \fIname\fR after and including the
last dot in \fIname\fR.  If there is no dot in \fIname\fR then return
the empty string.
.TP
\fBfile \fBisdirectory \fIname\fR
Return \fB1\fR if file \fIname\fR is a directory,
\fB0\fR otherwise.
.TP
\fBfile \fBisfile \fIname\fR
Return \fB1\fR if file \fIname\fR is a regular file,
\fB0\fR otherwise.
.TP
\fBfile lstat \fIname varName\fR
Same as \fBstat\fR option (see below) except uses the \fIlstat\fR
kernel call instead of \fIstat\fR.  This means that if \fIname\fR
refers to a symbolic link the information returned in \fIvarName\fR
is for the link rather than the file it refers to.  On systems that
don't support symbolic links this option behaves exactly the same
as the \fBstat\fR option.
.TP
\fBfile \fBmtime \fIname\fR
Return a decimal string giving the time at which file \fIname\fR
was last modified.  The time is measured in the standard UNIX
fashion as seconds from a fixed starting time (often January 1, 1970).
If the file doesn't exist or its modified time cannot be queried then an
error is generated.
.TP
\fBfile \fBowned \fIname\fR
Return \fB1\fR if file \fIname\fR is owned by the current user,
\fB0\fR otherwise.
.TP
\fBfile \fBreadable \fIname\fR
Return \fB1\fR if file \fIname\fR is readable by
the current user, \fB0\fR otherwise.
.TP
\fBfile readlink \fIname\fR
Returns the value of the symbolic link given by \fIname\fR (i.e. the
name of the file it points to).  If
\fIname\fR isn't a symbolic link or its value cannot be read, then
an error is returned.  On systems that don't support symbolic links
this option is undefined.
.TP
\fBfile \fBrootname \fIname\fR
Return all of the characters in \fIname\fR up to but not including
the last ``.'' character in the name.  If \fIname\fR doesn't contain
a dot, then return \fIname\fR.
.TP
\fBfile \fBsize \fIname\fR
Return a decimal string giving the size of file \fIname\fR in bytes.
If the file doesn't exist or its size cannot be queried then an
error is generated.
.TP
\fBfile \fBstat  \fIname varName\fR
Invoke the \fBstat\fR kernel call on \fIname\fR, and use the
variable given by \fIvarName\fR to hold information returned from
the kernel call.
\fIVarName\fR is treated as an array variable,
and the following elements of that variable are set: \fBatime\fR,
\fBctime\fR, \fBdev\fR, \fBgid\fR, \fBino\fR, \fBmode\fR, \fBmtime\fR,
\fBnlink\fR, \fBsize\fR, \fBtype\fR, \fBuid\fR.
Each element except \fBtype\fR is a decimal string with the value of
the corresponding field from the \fBstat\fR return structure; see the
manual entry for \fBstat\fR for details on the meanings of the values.
The \fBtype\fR element gives the type of the file in the same form
returned by the command \fBfile type\fR.
This command returns an empty string.
.TP
\fBfile \fBtail \fIname\fR
Return all of the characters in \fIname\fR after the last slash.
If \fIname\fR contains no slashes then return \fIname\fR.
.TP
\fBfile \fBtype \fIname\fR
Returns a string giving the type of file \fIname\fR, which will be
one of \fBfile\fR, \fBdirectory\fR, \fBcharacterSpecial\fR,
\fBblockSpecial\fR, \fBfifo\fR, \fBlink\fR, or \fBsocket\fR.
.TP
\fBfile \fBwritable \fIname\fR
Return \fB1\fR if file \fIname\fR is writable by
the current user, \fB0\fR otherwise.
.RE
.IP
The \fBfile\fR commands that return 0/1 results are often used in
conditional or looping commands, for example:
.RS
.DS
\fBif {![file exists foo]} then {error {bad file name}} else {...}\fR
.DE
.VE
.RE
.TP
\fBflush \fIfileId\fR
.VS
Flushes any output that has been buffered for \fIfileId\fR.
\fIFileId\fR must have been the return
value from a previous call to \fBopen\fR, or it may be
\fBstdout\fR or \fBstderr\fR to access one of the standard I/O streams;
it must refer to a file that was opened for writing.
This command returns an empty string.
.VE
.TP
\fBfor \fIstart test next body\fR
\fBFor\fR is a looping command, similar in structure to the C
\fBfor\fR statement.  The \fIstart\fR, \fInext\fR, and
\fIbody\fR arguments must be Tcl command strings, and \fItest\fR
is an expression string.
The \fBfor\fR command first invokes the Tcl interpreter to
execute \fIstart\fR.  Then it repeatedly evaluates \fItest\fR as
an expression; if the result is non-zero it invokes the Tcl
interpreter on \fIbody\fR, then invokes the Tcl interpreter on \fInext\fR,
then repeats the loop.  The command terminates when \fItest\fR evaluates
to 0.  If a \fBcontinue\fR command is invoked within \fIbody\fR then
any remaining commands in the current execution of \fIbody\fR are skipped;
processing continues by invoking the Tcl interpreter on \fInext\fR, then
evaluating \fItest\fR, and so on.  If a \fBbreak\fR command is invoked
within \fIbody\fR
or \fInext\fR,
then the \fBfor\fR command will
return immediately.
The operation of \fBbreak\fR and \fBcontinue\fR are similar to the
corresponding statements in C.
\fBFor\fR returns an empty string.
.TP
\fBforeach \fIvarname list body\fR
In this command, \fIvarname\fR is the name of a variable, \fIlist\fR
is a list of values to assign to \fIvarname\fR, and \fIbody\fR is a
collection of Tcl commands.  For each field in \fIlist\fR (in order
from left to right), \fBforeach\fR assigns the contents of the
field to \fIvarname\fR (as if the \fBlindex\fR command had been used
to extract the field), then calls the Tcl interpreter to execute
\fIbody\fR.  The \fBbreak\fR and \fBcontinue\fR statements may be
invoked inside \fIbody\fR, with the same effect as in the \fBfor\fR
command.  \fBForeach\fR returns an empty string.
.TP
\fBformat \fIformatString \fR?\fIarg arg ...\fR?
This command generates a formatted string in the same way as the
C \fBsprintf\fR procedure (it uses \fBsprintf\fR in its
implementation).  \fIFormatString\fR indicates how to format
the result, using \fB%\fR fields as in \fBsprintf\fR, and the additional
arguments, if any, provide values to be substituted into the result.
All of the \fBsprintf\fR options are valid; see the \fBsprintf\fR
man page for details.  Each \fIarg\fR must match the expected type
from the \fB%\fR field in \fIformatString\fR; the \fBformat\fR command
converts each argument to the correct type (floating, integer, etc.)
before passing it to \fBsprintf\fR for formatting.
The only unusual conversion is for \fB%c\fR; in this case the argument
must be a decimal string, which will then be converted to the corresponding
ASCII character value.
\fBFormat\fR does backslash substitution on its \fIformatString\fR
argument, so backslash sequences in \fIformatString\fR will be handled
correctly even if the argument is in braces.
The return value from \fBformat\fR
is the formatted string.
.TP
\fBgets \fIfileId\fR ?\fIvarName\fR?
.VS
Reads the next line from the file given by \fIfileId\fR and discards
the terminating newline character.
If \fIvarName\fR is specified, then the line is placed in the variable
by that name and the return value is a count of the number of characters
read (not including the newline).
If the end of the file is reached before reading
any characters then \-1 is returned and \fIvarName\fR is set to an
empty string.
If \fIvarName\fR is not specified then the return value will be
the line (minus the newline character) or an empty string if
the end of the file is reached before reading any characters.
An empty string will also be returned if a line contains no characters
except the newline, so \fBeof\fR may have to be used to determine
what really happened.
If the last character in the file is not a newline character, then
\fBgets\fR behaves as if there were an additional newline character
at the end of the file.
\fIFileId\fR must be \fBstdin\fR or the return value from a previous
call to \fBopen\fR; it must refer to a file that was opened
for reading.
.VE
.TP
\fBglob \fR?\fB\-nocomplain\fR? \fIfilename\fR ?\fIfilename ...\fR?
This command performs filename globbing, using csh rules.  The returned
value from \fBglob\fR is the list of expanded filenames.
.VS
If \fB\-nocomplain\fR is specified as the first argument then an empty
list may be returned;  otherwise an error is returned if the expanded
list is empty.  The \fB\-nocomplain\fR argument must be provided
exactly: an abbreviation will not be accepted.
.VE
.TP
\fBglobal \fIvarname \fR?\fIvarname ...\fR?
This command is ignored unless a Tcl procedure is being interpreted.
If so, then it declares the given \fIvarname\fR's to be global variables
rather than local ones.  For the duration of the current procedure
(and only while executing in the current procedure), any reference to
any of the \fIvarname\fRs will be bound to a global variable instead
of a local one.
.TP
\fBhistory \fR?\fIoption\fR? ?\fIarg arg ...\fR?
Note:  this command may not be available in all Tcl-based applications.
Typically, only those that receive command input in a typescript
form will support history.
The \fBhistory\fR command performs one of several operations related to
recently-executed commands recorded in a history list.  Each of
these recorded commands is referred to as an ``event''.  When
specifying an event to the \fBhistory\fR command, the following
forms may be used:
.RS
.IP [1]
A number:  if positive, it refers to the event with
that number (all events are numbered starting at 1).  If the number
is negative, it selects an event relative to the current event
(\fB\-1\fR refers to the previous event, \fB\-2\fR to the one before that, and
so on).
.IP [2]
A string:  selects the most recent event that matches the string.
An event is considered to match the string either if the string is
the same as the first characters of the event, or if the string
matches the event in the sense of the \fBstring match\fR command.
.LP
The \fBhistory\fR command can take any of the following forms:
.TP
\fBhistory\fR
Same
.VS
as \fBhistory info\fR, described below.
.VE
.TP
\fBhistory add\fI command \fR?\fBexec\fR?
Add the \fIcommand\fR argument to the history list as a new event.  If
\fBexec\fR is specified (or abbreviated) then the command is also
executed and its result is returned.  If \fBexec\fR isn't specified
then an empty string is returned as result.
.TP
\fBhistory change\fI newValue\fR ?\fIevent\fR?
Replace the value recorded for an event with \fInewValue\fR.  \fIEvent\fR
specifies the event to replace, and
defaults to the \fIcurrent\fR event (not event \fB\-1\fR).  This command
is intended for use in commands that implement new forms of history
substitution and wish to replace the current event (which invokes the
substitution) with the command created through substitution.  The return
value is an empty string.
.TP
\fBhistory event\fR ?\fIevent\fR?
Returns the value of the event given by \fIevent\fR.  \fIEvent\fR
defaults to \fB\-1\fR.  This command causes history revision to occur:
see below for details.
.TP
\fBhistory info \fR?\fIcount\fR?
Returns a formatted string (intended for humans to read) giving
the event number and contents for each of the events in the history
list except the current event.  If \fIcount\fR is specified
then only the most recent \fIcount\fR events are returned.
.TP
\fBhistory keep \fIcount\fR
This command may be used to change the size of the history list to
\fIcount\fR events.  Initially, 20 events are retained in the history
list.  This command returns an empty string.
.TP
\fBhistory nextid\fR
Returns the number of the next event to be recorded
in the history list.  It is useful for things like printing the
event number in command-line prompts.
.TP
\fBhistory redo \fR?\fIevent\fR?
Re-execute the command indicated by \fIevent\fR and return its result.
\fIEvent\fR defaults to \fB\-1\fR.  This command results in history
revision:  see below for details.
.TP
\fBhistory substitute \fIold new \fR?\fIevent\fR?
Retrieve the command given by \fIevent\fR
(\fB\-1\fR by default), replace any occurrences of \fIold\fR by
\fInew\fR in the command (only simple character equality is supported;
no wild cards), execute the resulting command, and return the result
of that execution.  This command results in history
revision:  see below for details.
.TP
\fBhistory words \fIselector\fR ?\fIevent\fR?
Retrieve from the command given by \fIevent\fR (\fB\-1\fR by default)
the words given by \fIselector\fR, and return those words in a string
separated by spaces.  The \fBselector\fR argument has three forms.
If it is a single number then it selects the word given by that
number (\fB0\fR for the command name, \fB1\fR for its first argument,
and so on).  If it consists of two numbers separated by a dash,
then it selects all the arguments between those two.  Otherwise
\fBselector\fR is treated as a pattern; all words matching that
pattern (in the sense of \fBstring match\fR) are returned.  In
the numeric forms \fB$\fR may be used
to select the last word of a command.
For example, suppose the most recent command in the history list is
.RS
.DS
\fBformat  {%s is %d years old} Alice [expr $ageInMonths/12]\fR
.DE
Below are some history commands and the results they would produce:
.DS
.ta 4c
.fi
.UL Command "    "
.UL Result
.nf

\fBhistory words $    [expr $ageInMonths/12]\fR
\fBhistory words 1-2    {%s is %d years  old} Alice\fR
\fBhistory words *a*o*    {%s is %d years old} [expr $ageInMonths/12]\fR
.DE
\fBHistory words\fR results in history revision:  see below for details.
.RE
The history options \fBevent\fR, \fBredo\fR, \fBsubstitute\fR,
and \fBwords\fR result in ``history revision''.
When one of these options is invoked then the current event
is modified to eliminate the history command and replace it with
the result of the history command.
For example, suppose that the most recent command in the history
list is
.DS
\fBset a [expr $b+2]\fR
.DE
and suppose that the next command invoked is one of the ones on
the left side of the table below.  The command actually recorded in
the history event will be the corresponding one on the right side
of the table.
.ne 1.5c
.DS
.ta 4c
.fi
.UL "Command Typed" "    "
.UL "Command Recorded"
.nf

\fBhistory redo    set a [expr $b+2]\fR
\fBhistory s a b    set b [expr $b+2]\fR
\fBset c [history w 2]    set c [expr $b+2]\fR
.DE
.VS
History revision is needed because event specifiers like \fB\-1\fR
are only valid at a particular time:  once more events have been
added to the history list a different event specifier would be
needed.
History revision occurs even when \fBhistory\fR is invoked
indirectly from the current event (e.g. a user types a command
that invokes a Tcl procedure that invokes \fBhistory\fR):  the
top-level command whose execution eventually resulted in a
\fBhistory\fR command is replaced.
If you wish to invoke commands like \fBhistory words\fR without
history revision, you can use \fBhistory event\fR to save the
current history event and then use \fBhistory change\fR to
restore it later.
.VE
.VE
.RE
.TP
\fBif \fItest \fR?\fBthen\fR? \fItrueBody \fR?\fBelse\fR? ?\fIfalseBody\fR?
The \fIif\fR command evaluates \fItest\fR as an expression (in the
same way that \fBexpr\fR evaluates its argument).  The value of the
expression must be numeric; if it
is non-zero then \fItrueBody\fR is called by passing it to the
Tcl interpreter.  Otherwise \fIfalseBody\fR is executed by passing it to
the Tcl interpreter.  The \fBthen\fR and \fBelse\fR arguments are optional
``noise words'' to make the command easier to read.  \fIFalseBody\fR is
also optional; if it isn't specified then the command does nothing if
\fItest\fR evaluates to zero.  The return value from \fBif\fR is
the value of the last command executed in \fItrueBody\fR or
\fIfalseBody\fR, or the empty string if \fItest\fR evaluates to zero and
\fIfalseBody\fR isn't specified.
.TP
\fBincr \fIvarName \fR?\fIincrement\fR?
.VS
Increment the value stored in the variable whose name is \fIvarName\fR.
The value of the variable must be integral.
If \fIincrement\fR is supplied then its value (which must be an
integer) is added to the value of variable \fIvarName\fR;  otherwise
1 is added to \fIvarName\fR.
The new value is stored as a decimal string in variable \fIvarName\fR
and also returned as result.
.VE
.TP
\fBinfo \fIoption \fR?\fIarg arg ...\fR?
Provide information about various internals to the Tcl interpreter.
The legal \fIoption\fR's (which may be abbreviated) are:
.RS
.TP
\fBinfo args \fIprocname\fR
Returns a list containing the names of the arguments to procedure
\fIprocname\fR, in order.  \fIProcname\fR must be the name of a
Tcl command procedure.
.TP
\fBinfo body \fIprocname\fR
Returns the body of procedure \fIprocname\fR.  \fIProcname\fR must be
the name of a Tcl command procedure.
.TP
\fBinfo cmdcount\fR
Returns a count of the total number of commands that have been invoked
in this interpreter.
.TP
\fBinfo commands \fR?\fIpattern\fR?
If \fIpattern\fR isn't specified, returns a list of names of all the
Tcl commands, including both the built-in commands written in C and
the command procedures defined using the \fBproc\fR command.
If \fIpattern\fR is specified, only those names matching \fIpattern\fR
are returned.  Matching is determined using the same rules as for
\fBstring match\fR.
.TP
\fBinfo complete \fIcommand\fR
.VS
Returns 1 if \fIcommand\fR is a complete Tcl command in the sense of
having no unclosed quotes, braces, brackets or array element names,
If the command doesn't appear to be complete then 0 is returned.
This command is typically used in line-oriented input environments
to allow users to type in commands that span multiple lines;  if the
command isn't complete, the script can delay evaluating it until additional
lines have been typed to complete the command.
.VE
.TP
\fBinfo default \fIprocname arg varname\fR
\fIProcname\fR must be the name of a Tcl command procedure and \fIarg\fR
must be the name of an argument to that procedure.  If \fIarg\fR
doesn't have a default value then the command returns \fB0\fR.
Otherwise it returns \fB1\fR and places the default value of \fIarg\fR
into variable \fIvarname\fR.
.TP
\fBinfo exists \fIvarName\fR
Returns \fB1\fR if the variable named \fIvarName\fR exists in the
current context (either as a global or local variable), returns \fB0\fR
otherwise.
.TP
\fBinfo globals \fR?\fIpattern\fR?
If \fIpattern\fR isn't specified, returns a list of all the names
of currently-defined global variables.
If \fIpattern\fR is specified, only those names matching \fIpattern\fR
are returned.  Matching is determined using the same rules as for
\fBstring match\fR.
.TP
\fBinfo level\fR ?\fInumber\fR?
If \fInumber\fR is not specified, this command returns a number
giving the stack level of the invoking procedure, or 0 if the
command is invoked at top-level.  If \fInumber\fR is specified,
then the result is a list consisting of the name and arguments for the
procedure call at level \fInumber\fR on the stack.  If \fInumber\fR
is positive then it selects a particular stack level (1 refers
to the top-most active procedure, 2 to the procedure it called, and
so on); otherwise it gives a level relative to the current level
(0 refers to the current procedure, -1 to its caller, and so on).
See the \fBuplevel\fR command for more information on what stack
levels mean.
.TP
\fBinfo library\fR
.VS
Returns the name of the library directory in which standard Tcl
scripts are stored.
The default value for the library is compiled into Tcl, but it
.VS
may be overridden by setting the TCL_LIBRARY environment variable.
If there is no TCL_LIBRARY variable and no compiled-in value then
and error is generated.
.VE
See the \fBlibrary\fR manual entry for details of the facilities
provided by the Tcl script library.
Normally each application will have its own application-specific
script library in addition to the Tcl script library;  I suggest that
each application set a global variable with a name like
.VS
\fB$\fIapp\fB_library\fR (where \fIapp\fR is the application's name)
.VE
to hold the location of that application's library directory.
.VE
.TP
\fBinfo locals \fR?\fIpattern\fR?
If \fIpattern\fR isn't specified, returns a list of all the names
of currently-defined local variables, including arguments to the
current procedure, if any.
.VS
Variables defined with the \fBglobal\fR and \fBupvar\fR commands
will not be returned.
.VE
If \fIpattern\fR is specified, only those names matching \fIpattern\fR
are returned.  Matching is determined using the same rules as for
\fBstring match\fR.
.TP
\fBinfo procs \fR?\fIpattern\fR?
If \fIpattern\fR isn't specified, returns a list of all the
names of Tcl command procedures.
If \fIpattern\fR is specified, only those names matching \fIpattern\fR
are returned.  Matching is determined using the same rules as for
\fBstring match\fR.
.TP
\fBinfo script\fR
.VS
If a Tcl script file is currently being evaluated (i.e. there is a
call to \fBTcl_EvalFile\fR active or there is an active invocation
of the \fBsource\fR command), then this command returns the name
of the innermost file being processed.  Otherwise the command returns an
empty string.
.VE
.TP
\fBinfo tclversion\fR
Returns the version number for this version of Tcl in the form \fIx.y\fR,
where changes to \fIx\fR represent major changes with probable
incompatibilities and changes to \fIy\fR represent small enhancements and
bug fixes that retain backward compatibility.
.TP
\fBinfo vars\fR ?\fIpattern\fR?
If \fIpattern\fR isn't specified,
returns a list of all the names of currently-visible variables, including
both locals and currently-visible globals.
If \fIpattern\fR is specified, only those names matching \fIpattern\fR
are returned.  Matching is determined using the same rules as for
\fBstring match\fR.
.RE
.TP
\fBjoin \fIlist \fR?\fIjoinString\fR?
.VS
The \fIlist\fR argument must be a valid Tcl list.
This command returns the string
formed by joining all of the elements of \fIlist\fR together with
\fIjoinString\fR separating each adjacent pair of elements.
The \fIjoinString\fR argument defaults to a space character.
.VE
.TP
\fBlappend \fIvarName value \fR?\fIvalue value ...\fR?
.VS
Treat the variable given by \fIvarName\fR as a list and append
each of the \fIvalue\fR arguments to that list as a separate
element, with spaces between elements.
If \fIvarName\fR doesn't exist, it is created as a list with elements
given by the \fIvalue\fR arguments.
\fBLappend\fR is similar to \fBappend\fR except that the \fIvalue\fRs
are appended as list elements rather than raw text.
This command provides a relatively efficient way to build up
large lists.  For example, ``\fBlappend a $b\fR'' is much
more efficient than ``\fBset a [concat $a [list $b]]\fR'' when
\fB$a\fR is long.
.TP
\fBlindex \fIlist index\fR
Treats \fIlist\fR as a Tcl list and returns the \fIindex\fR'th element
from it (0 refers to the first element of the list).
In extracting the element, \fIlindex\fR observes the same rules
concerning braces and quotes and backslashes as the Tcl command
interpreter; however, variable
substitution and command substitution do not occur.
If \fIindex\fR is negative or greater than or equal to the number
of elements in \fIvalue\fR, then an empty
string is returned.
.TP
\fBlinsert \fIlist index element \fR?\fIelement element ...\fR?
This command produces a new list from \fIlist\fR by inserting all
of the \fIelement\fR arguments just before the \fIindex\fRth
element of \fIlist\fR.  Each \fIelement\fR argument will become
a separate element of the new list.  If \fIindex\fR is less than
or equal to zero, then the new elements are inserted at the
beginning of the list.  If \fIindex\fR is greater than or equal
to the number of elements in the list, then the new elements are
appended to the list.
.VE
.TP
\fBlist \fIarg \fR?\fIarg ...\fR?
This command returns a list comprised of all the \fIarg\fRs.  Braces
and backslashes get added as necessary, so that the \fBindex\fR command
may be used on the result to re-extract the original arguments, and also
so that \fBeval\fR may be used to execute the resulting list, with
\fIarg1\fR comprising the command's name and the other \fIarg\fRs comprising
its arguments.  \fBList\fR produces slightly different results than
\fBconcat\fR:  \fBconcat\fR removes one level of grouping before forming
the list, while \fBlist\fR works directly from the original arguments.
For example, the command
.RS
.DS
\fBlist a b {c d e} {f {g h}}
.DE
will return
.DS
\fBa b {c d e} {f {g h}}
.DE
while \fBconcat\fR with the same arguments will return
.DS
\fBa b c d e f {g h}\fR
.DE
.RE
.br
.VS
.TP
\fBllength \fIlist\fR
Treats \fIlist\fR as a list and returns a decimal string giving
the number of elements in it.
.TP
\fBlrange \fIlist first last
\fIList\fR must be a valid Tcl list.  This command will
return a new list consisting of elements
\fIfirst\fR through \fIlast\fR, inclusive.
\fILast\fR may be \fBend\fR (or any
abbreviation of it) to refer to the last element of the list.
If \fIfirst\fR is less than zero, it is treated as if it were zero.
If \fIlast\fR is greater than or equal to the number of elements
in the list, then it is treated as if it were \fBend\fR.
If \fIfirst\fR is greater than \fIlast\fR then an empty string
is returned.
Note: ``\fBlrange \fIlist first first\fR'' does not always produce the
same result as ``\fBlindex \fIlist first\fR'' (although it often does
for simple fields that aren't enclosed in braces); it does, however,
produce exactly the same results as ``\fBlist [lindex \fIlist first\fB]\fR''
.TP
\fBlreplace \fIlist first last \fR?\fIelement element ...\fR?
Returns a new list formed by replacing one or more elements of
\fIlist\fR with the \fIelement\fR arguments.
\fIFirst\fR gives the index in \fIlist\fR of the first element
to be replaced.
If \fIfirst\fR is less than zero then it refers to the first
element of \fIlist\fR;  the element indicated by \fIfirst\fR
must exist in the list.
\fILast\fR gives the index in \fIlist\fR of the last element
to be replaced;  it must be greater than or equal to \fIfirst\fR.
\fILast\fR may be \fBend\fR (or any abbreviation of it) to indicate
that all elements between \fIfirst\fR and the end of the list should
be replaced.
The \fIelement\fR arguments specify zero or more new arguments to
be added to the list in place of those that were deleted.
Each \fIelement\fR argument will become a separate element of
the list.
If no \fIelement\fR arguments are specified, then the elements
between \fIfirst\fR and \fIlast\fR are simply deleted.
.TP
\fBlsearch \fIlist pattern\fR
Search the elements of \fIlist\fR to see if one of them matches
\fIpattern\fR.
If so, the command returns the index of the first matching
element.
If not, the command returns \fB\-1\fR.
Pattern matching is done in the same way as for the \fBstring match\fR
command.
.TP
\fBlsort \fIlist\fR
Sort the elements of \fIlist\fR, returning a new list in sorted
order.
ASCII sorting is used, with the result in increasing order.
.VE
.TP
\fBopen \fIfileName\fR ?\fIaccess\fR?
.VS
Opens a file and returns an identifier
that may be used in future invocations
of commands like \fBread\fR, \fBputs\fR, and \fBclose\fR.
\fIFileName\fR gives the name of the file to open; if it starts with
a tilde then tilde substitution is performed as described for
\fBTcl_TildeSubst\fR.
If the first character of \fIfileName\fR is ``|'' then the
remaining characters of \fIfileName\fR are treated as a command
pipeline to invoke, in the same style as for \fBexec\fR.
In this case, the identifier returned by \fBopen\fR may be used
to write to the command's input pipe or read from its output pipe.
The \fIaccess\fR argument indicates the way in which the file
(or command pipeline) is to be accessed.
It may have any of the following values:
.RS
.TP
\fBr\fR
Open the file for reading only; the file must already exist.
.TP
\fBr+\fR
Open the file for both reading and writing; the file must
already exist.
.TP
\fBw\fR
Open the file for writing only.  Truncate it if it exists.  If it doesn't
exist, create a new file.
.TP
\fBw+\fR
Open the file for reading and writing.  Truncate it if it exists.
If it doesn't exist, create a new file.
.TP
\fBa\fR
Open the file for writing only.  The file must already exist, and the file
is positioned so that new data is appended to the file.
.TP
\fBa+\fR
Open the file for reading and writing.  If the file doesn't exist,
create a new empty file.
Set the initial access position  to the end of the file.
.PP
\fIAccess\fR defaults to \fBr\fR.
If a file is opened for both reading and writing, then \fBseek\fR
must be invoked between a read and a write, or vice versa (this
restriction does not apply to command pipelines opened with \fBopen\fR).
When \fIfileName\fR specifies a command pipeline and a write-only access
is used, then standard output from the pipeline is directed to the
current standard output unless overridden by the command.
When \fIfileName\fR specifies a command pipeline and a read-only access
is used, then standard input from the pipeline is taken from the
current standard input unless overridden by the command.
.RE
.VE
.TP
\fBproc \fIname args body\fR
The \fBproc\fR command creates a new Tcl command procedure,
\fIname\fR, replacing
any existing command there may have been by that name.  Whenever the
new command is invoked, the contents of \fIbody\fR will be executed
by the Tcl interpreter.  \fIArgs\fR specifies the formal arguments to the
procedure.  It consists of a list, possibly empty, each of whose
elements specifies
one argument.  Each argument specifier is also a list with either
one or two fields.  If there is only a single field in the specifier,
then it is the name of the argument; if there are two fields, then
the first is the argument name and the second is its default value.
braces and backslashes may be used in the usual way to specify
complex default values.
.IP
When \fIname\fR is invoked, a local variable
will be created for each of the formal arguments to the procedure; its
value will be the value of corresponding argument in the invoking command
or the argument's default value.
Arguments with default values need not be
specified in a procedure invocation.  However, there must be enough
actual arguments for all the
formal arguments that don't have defaults, and there must not be any extra
actual arguments.  There is one special case to permit procedures with
variable numbers of arguments.  If the last formal argument has the name
\fBargs\fR, then a call to the procedure may contain more actual arguments
than the procedure has formals.  In this case, all of the actual arguments
starting at the one that would be assigned to \fBargs\fR are combined into
a list (as if the \fBlist\fR command had been used); this combined value
is assigned to the local variable \fBargs\fR.
.IP
When \fIbody\fR is being executed, variable names normally refer to
local variables, which are created automatically when referenced and
deleted when the procedure returns.  One local variable is automatically
created for each of the procedure's arguments.
Global variables can only be accessed by invoking
the \fBglobal\fR command.
.IP
The \fBproc\fR command returns the null string.  When a procedure is
invoked, the procedure's return value is the value specified in a
\fBreturn\fR command.  If the procedure doesn't execute an explicit
\fBreturn\fR, then its return value is the value of the last command
executed in the procedure's body.
If an error occurs while executing the procedure
body, then the procedure-as-a-whole will return that same error.
.TP
\fBputs \fIfileId string \fR?\fBnonewline\fR?
.VS
Writes the characters given by \fIstring\fR to the file given
by \fIfileId\fR.
\fBPuts\fR normally outputs a newline character after \fIstring\fR,
but this feature may be suppressed by specifying the \fBnonewline\fR
argument.
Output to files is buffered internally by Tcl; the \fBflush\fR
command may be used to force buffered characters to be output.
\fIFileId\fR must have been the return
value from a previous call to \fBopen\fR, or it may be
\fBstdout\fR or \fBstderr\fR to refer to one of the standard I/O
channels; it must refer to a file that was opened for
writing.
.TP
\fBpwd\fR
.br
Returns the path name of the current working directory.
.TP
\fBread \fIfileId\fR
.TP
\fBread \fIfileId \fBnonewline\fR
.TP
\fBread \fIfileId numBytes\fR
In the first form, all of the remaining bytes are read from the file
given by \fIfileId\fR; they are returned as the result of the command.
If \fBnonewline\fR is specified as an additional argument, then the last
character of the file is discarded if it is a newline.
In the third form, the extra argument specifies how many bytes to read;
exactly this many bytes will be read and returned, unless there are fewer than
\fInumBytes\fR bytes left in the file; in this case, all the remaining
bytes are returned.
\fIFileId\fR must be \fBstdin\fR or the return
value from a previous call to \fBopen\fR; it must
refer to a file that was opened for reading.
.TP
\fBregexp \fR?\fB\-indices\fR? \fR?\fB\-nocase\fR? \fIexp string \fR?\fImatchVar\fR? ?\fIsubMatchVar subMatchVar ...\fR?
Determines whether the regular expression \fIexp\fR matches part or
all of \fIstring\fR and returns 1 if it does, 0 if it doesn't.
See REGULAR EXPRESSIONS above for complete information on the
syntax of \fIexp\fR and how it is matched against \fIstring\fR.
.RS
.LP
If the \fB\-nocase\fR switch is specified then upper-case
characters in \fIstring\fR
are treated as lower case during the matching process.
The \fB\-nocase\fR switch must be specified before \fIexp\fR and
may not be abbreviated.
.LP
If additional arguments are specified after \fIstring\fR then they
are treated as the names of variables to use to return
information about which part(s) of \fIstring\fR matched \fIexp\fR.
\fIMatchVar\fR will be set to the range of \fIstring\fR that
matched all of \fIexp\fR.  The first \fIsubMatchVar\fR will contain
the characters in \fIstring\fR that matched the leftmost parenthesized
subexpression within \fIexp\fR, the next \fIsubMatchVar\fR will
contain the characters that matched the next parenthesized
subexpression to the right in \fIexp\fR, and so on.
.LP
Normally, \fImatchVar\fR and the \fIsubMatchVar\fRs are set to hold
the matching characters from \fBstring\fR.
However, if the \fB\-indices\fR switch is specified then each variable
will contain a list of two decimal strings giving the indices
in \fIstring\fR of the first and last characters in the matching
range of characters.
The \fB\-indices\fR switch must be specified before the \fIexp\fR
argument and may not be abbreviated.
.LP
If there are more \fIsubMatchVar\fR's than parenthesized
subexpressions within \fIexp\fR, or if a particular subexpression
in \fIexp\fR doesn't match the string (e.g. because it was in a
portion of the expression that wasn't matched), then the corresponding
\fIsubMatchVar\fR will be set to ``\fB\-1 \-1\fR'' if \fB\-indices\fR
has been specified or to an empty string otherwise.
.RE
.TP
\fBregsub \fR?\fB\-all\fR? ?\fB\-nocase\fR? \fIexp string subSpec varName\fR
This command matches the regular expression \fIexp\fR against
\fIstring\fR using the rules described in REGULAR EXPRESSIONS
above.
If there is no match, then the command returns 0 and does nothing
else.
If there is a match, then the command returns 1 and also copies
\fIstring\fR to the variable whose name is given by \fIvarName\fR.
When copying \fIstring\fR, the portion of \fIstring\fR that
matched \fIexp\fR is replaced with \fIsubSpec\fR.
If \fIsubSpec\fR contains a ``&'' or ``\e0'', then it is replaced
in the substitution with the portion of \fIstring\fR that
matched \fIexp\fR.
If \fIsubSpec\fR contains a ``\e\fIn\fR'', where \fIn\fR is a digit
between 1 and 9, then it is replaced in the substitution with
the portion of \fIstring\fR that matched the \fIn\fR-th
parenthesized subexpression of \fIexp\fR.
Additional backslashes may be used in \fIsubSpec\fR to prevent special
interpretation of ``&'' or ``\e0'' or ``\e\fIn\fR'' or
backslash.
The use of backslashes in \fIsubSpec\fR tends to interact badly
with the Tcl parser's use of backslashes, so it's generally
safest to enclose \fIsubSpec\fR in braces if it includes
backslashes.
If the \fB\-all\fR argument is specified, then all ranges in
\fIstring\fR that match \fIexp\fR are found and substitution is
performed for each of these ranges;  otherwise only the first
matching range is found and substituted.
If \fB\-all\fR is specified, then ``&'' and ``\e\fIn\fR''
sequences are handled for each substitution using the information
from the corresponding match.
If the \fB\-nocase\fR argument is specified, then upper-case
characters in \fIstring\fR are converted to lower-case before
matching against \fIexp\fR;  however, substitutions specified
by \fIsubSpec\fR use the original unconverted form of \fIstring\fR.
The \fB\-all\fR and \fB\-nocase\fR arguments must be specified
exactly:  no abbreviations are permitted.
.VE
.TP
\fBrename \fIoldName newName\fR
Rename the command that used to be called \fIoldName\fR so that it
is now called \fInewName\fR.  If \fInewName\fR is an empty string
(e.g. {}) then \fIoldName\fR is deleted.  The \fBrename\fR command
returns an empty string as result.
.TP
\fBreturn \fR?\fIvalue\fR?
Return immediately from the current procedure
(or top-level command or \fBsource\fR command),
with \fIvalue\fR as the return value.  If \fIvalue\fR is not specified,
an empty string will be returned as result.
.TP
\fBscan \fIstring format varname1 \fR?\fIvarname2 ...\fR?
This command parses fields from an input string in the same fashion
as the C \fBsscanf\fR procedure.  \fIString\fR gives the input to
be parsed and \fIformat\fR indicates how to parse it, using \fB%\fR
fields as in \fBsscanf\fR.  All of the \fBsscanf\fR options are valid;
see the \fBsscanf\fR man page for details.  Each \fIvarname\fR gives
the name of a variable; when a field is scanned from \fIstring\fR,
the result is converted back into a string and assigned to the
corresponding \fIvarname\fR.  The only unusual conversion is for
\fB%c\fR.  For \fB%c\fR conversions a single character value is
converted to a decimal string, which is then assigned to the
corresponding \fIvarname\fR;
.VS
no field width may be specified for this conversion.
.TP
\fBseek \fIfileId offset \fR?\fIorigin\fR?
Change the current access position for \fIfileId\fR.
The \fIoffset\fR and \fIorigin\fR arguments specify the position at
which the next read or write will occur for \fIfileId\fR.
\fIOffset\fR must be a number (which may be negative) and \fIorigin\fR
must be one of the following:
.RS
.TP
\fBstart\fR
The new access position will be \fIoffset\fR bytes from the start
of the file.
.TP
\fBcurrent\fR
The new access position will be \fIoffset\fR bytes from the current
access position; a negative \fIoffset\fR moves the access position
backwards in the file.
.TP
\fBend\fR
The new access position will be \fIoffset\fR bytes from the end of
the file.  A negative \fIoffset\fR places the access position before
the end-of-file, and a positive \fIoffset\fR places the access position
after the end-of-file.
.LP
The \fIorigin\fR argument defaults to \fBstart\fR.
\fIFileId\fR must have been the return
value from a previous call to \fBopen\fR, or it may be \fBstdin\fR,
\fBstdout\fR, or \fBstderr\fR to refer to one of the standard I/O
channels.
This command returns an empty string.
.RE
.VE
.TP
\fBset \fIvarname \fR?\fIvalue\fR?
Returns the value of variable \fIvarname\fR.
If \fIvalue\fR is specified, then set
the value of \fIvarname\fR to \fIvalue\fR, creating a new variable
if one doesn't already exist, and return its value.
.VS
If \fIvarName\fR contains an open parenthesis and ends with a
close parenthesis, then it refers to an array element:  the characters
before the open parenthesis are the name of the array, and the characters
between the parentheses are the index within the array.
Otherwise \fIvarName\fR refers to a scalar variable.
.VE
If no procedure is active, then \fIvarname\fR refers to a global
variable.
If a procedure is active, then \fIvarname\fR refers to a parameter
or local variable of the procedure, unless the \fIglobal\fR command
has been invoked to declare \fIvarname\fR to be global.
.TP
\fBsource \fIfileName\fR
Read file \fIfileName\fR and pass the contents to the Tcl interpreter
as a sequence of commands to execute in the normal fashion.  The return
value of \fBsource\fR is the return value of the last command executed
from the file.  If an error occurs in executing the contents of the
file, then the \fBsource\fR command will return that error.
If a \fBreturn\fR command is invoked from within the file, the remainder of
the file will be skipped and the \fBsource\fR command will return
normally with the result from the \fBreturn\fR command.
If \fIfileName\fR starts with a tilde, then it is tilde-substituted
as described in the \fBTcl_TildeSubst\fR manual entry.
.TP
\fBsplit \fIstring \fR?\fIsplitChars\fR?
Returns a list created by splitting \fIstring\fR at each character
that is in the \fIsplitChars\fR argument.
Each element of the result list will consist of the
characters from \fIstring\fR between instances of the
characters in \fIsplitChars\fR.
Empty list elements will be generated if \fIstring\fR contains
adjacent characters in \fIsplitChars\fR, or if the first or last
character of \fIstring\fR is in \fIsplitChars\fR.
If \fIsplitChars\fR is an empty string then each character of
\fIstring\fR becomes a separate element of the result list.
\fISplitChars\fR defaults to the standard white-space characters.
For example,
.RS
.DS
\fBsplit "comp.unix.misc" .\fR
.DE
returns \fB"comp unix misc"\fR and
.DS
\fBsplit "Hello world" {}\fR
.DE
returns \fB"H e l l o { } w o r l d"\fR.
.VE
.RE
.TP
\fBstring \fIoption arg \fR?\fIarg ...?\fR
Perform one of several string operations, depending on \fIoption\fR.
The legal \fIoption\fRs (which may be abbreviated) are:
.RS
.TP
\fBstring compare \fIstring1 string2\fR
Perform a character-by-character comparison of strings \fIstring1\fR and
\fIstring2\fR in the same way as the C \fBstrcmp\fR procedure.  Return
-1, 0, or 1, depending on whether \fIstring1\fR is lexicographically
less than, equal to, or greater than \fIstring2\fR.
.TP
\fBstring first \fIstring1 string2\fR
Search \fIstring2\fR for a sequence of characters that exactly match
the characters in \fIstring1\fR.  If found, return the index of the
first character in the first such match within \fIstring2\fR.  If not
found, return -1.
.br
.VS
.TP
\fBstring index \fIstring charIndex\fR
Returns the \fIcharIndex\fR'th character of the \fIstring\fR
argument.  A \fIcharIndex\fR of 0 corresponds to the first
character of the string.
If \fIcharIndex\fR is less than 0 or greater than
or equal to the length of the string then an empty string is
returned.
.VE
.TP
\fBstring last \fIstring1 string2\fR
Search \fIstring2\fR for a sequence of characters that exactly match
the characters in \fIstring1\fR.  If found, return the index of the
first character in the last such match within \fIstring2\fR.  If there
is no match, then return \-1.
.br
.VS
.TP
\fBstring length \fIstring\fR
Returns a decimal string giving the number of characters in \fIstring\fR.
.VE
.TP
\fBstring match \fIpattern\fR \fIstring\fR
See if \fIpattern\fR matches \fIstring\fR; return 1 if it does, 0
if it doesn't.  Matching is done in a fashion similar to that
used by the C-shell.  For the two strings to match, their contents
must be identical except that the following special sequences
may appear in \fIpattern\fR:
.RS
.IP \fB*\fR 10
Matches any sequence of characters in \fIstring\fR,
including a null string.
.IP \fB?\fR 10
Matches any single character in \fIstring\fR.
.IP \fB[\fIchars\fB]\fR 10
Matches any character in the set given by \fIchars\fR.  If a sequence
of the form
\fIx\fB\-\fIy\fR appears in \fIchars\fR, then any character
between \fIx\fR and \fIy\fR, inclusive, will match.
.IP \fB\e\fIx\fR 10
Matches the single character \fIx\fR.  This provides a way of
avoiding the special interpretation of the characters
\fB*?[]\e\fR in \fIpattern\fR.
.RE
.br
.VS
.TP
\fBstring range \fIstring first last\fR
Returns a range of consecutive characters from \fIstring\fR, starting
with the character whose index is \fIfirst\fR and ending with the
character whose index is \fIlast\fR.  An index of 0 refers to the
first character of the string.  \fILast\fR may be \fBend\fR (or any
abbreviation of it) to refer to the last character of the string.
If \fIfirst\fR is less than zero then it is treated as if it were zero, and
if \fIlast\fR is greater than or equal to the length of the string then
it is treated as if it were \fBend\fR.  If \fIfirst\fR is greater than
\fIlast\fR then an empty string is returned.
.TP
\fBstring tolower \fIstring\fR
Returns a value equal to \fIstring\fR except that all upper case
letters have been converted to lower case.
.TP
\fBstring toupper \fIstring\fR
Returns a value equal to \fIstring\fR except that all lower case
letters have been converted to upper case.
.TP
\fBstring trim \fIstring\fR ?\fIchars\fR?
Returns a value equal to \fIstring\fR except that any leading
or trailing characters from the set given by \fIchars\fR are
removed.
If \fIchars\fR is not specified then white space is removed
(spaces, tabs, newlines, and carriage returns).
.TP
\fBstring trimleft \fIstring\fR ?\fIchars\fR?
Returns a value equal to \fIstring\fR except that any
leading characters from the set given by \fIchars\fR are
removed.
If \fIchars\fR is not specified then white space is removed
(spaces, tabs, newlines, and carriage returns).
.TP
\fBstring trimright \fIstring\fR ?\fIchars\fR?
Returns a value equal to \fIstring\fR except that any
trailing characters from the set given by \fIchars\fR are
removed.
If \fIchars\fR is not specified then white space is removed
(spaces, tabs, newlines, and carriage returns).
.RE
.TP
\fBtell \fIfileId\fR
Returns a decimal string giving the current access position in
\fIfileId\fR.
\fIFileId\fR must have been the return
value from a previous call to \fBopen\fR, or it may be \fBstdin\fR,
\fBstdout\fR, or \fBstderr\fR to refer to one of the standard I/O
channels.
.VE
.TP
\fBtime \fIcommand\fR ?\fIcount\fR?
This command will call the Tcl interpreter \fIcount\fR
times to execute \fIcommand\fR (or once if \fIcount\fR isn't
specified).  It will then return a string of the form
.RS
.DS
\fB503 microseconds per iteration\fR
.DE
which indicates the average amount of time required per iteration,
in microseconds.
Time is measured in elapsed time, not CPU time.
.RE
.TP
\fBtrace \fIoption\fR ?\fIarg arg ...\fR?
.VS
Cause Tcl commands to be executed whenever certain operations are
invoked.  At present, only variable tracing is implemented. The
legal \fIoption\fR's (which may be abbreviated) are:
.RS
.TP
\fBtrace variable \fIname ops command\fR
Arrange for \fIcommand\fR to be executed whenever variable \fIname\fR
is accessed in one of the ways given by \fIops\fR.  \fIName\fR may
refer to a normal variable, an element of an array, or to an array
as a whole (i.e. \fIname\fR may be just the name of an array, with no
parenthesized index).  If \fIname\fR refers to a whole array, then
\fIcommand\fR is invoked whenever any element of the array is
manipulated.
.RS
.LP
\fIOps\fR indicates which operations are of interest, and consists of
one or more of the following letters:
.RS
.TP
\fBr\fR
Invoke \fIcommand\fR whenever the variable is read.
.TP
\fBw\fR
Invoke \fIcommand\fR whenever the variable is written.
.TP
\fBu\fR
Invoke \fIcommand\fR whenever the variable is unset.  Variables
can be unset explicitly with the \fBunset\fR command, or
implicitly when procedures return (all of their local variables
are unset).  Variables are also unset when interpreters are
deleted, but traces will not be invoked because there is no
interpreter in which to execute them.
.RE
.LP
When the trace triggers, three arguments are appended to
\fIcommand\fR so that the actual command is as follows:
.DS C
\fIcommand name1 name2 op\fR
.DE
\fIName1\fR and \fIname2\fR give the name(s) for the variable
being accessed:  if the variable is a scalar then \fIname1\fR
gives the variable's name and \fIname2\fR is an empty string;
if the variable is an array element then \fIname1\fR gives the
name of the array and name2 gives the index into the array;
if an entire array is being deleted and the trace was registered
on the overall array, rather than a single element, then \fIname1\fR
gives the array name and \fIname2\fR is an empty string.
\fIOp\fR indicates what operation is being performed on the
variable, and is one of \fBr\fR, \fBw\fR, or \fBu\fR as
defined above.
.LP
\fICommand\fR executes in the same context as the code that invoked
the traced operation:  if the variable was accessed as part of a
Tcl procedure, then \fIcommand\fR will have access to the same
local variables as code in the procedure.  This context may be
different than the context in which the trace was created.
If \fIcommand\fR invokes a procedure (which it normally does) then
the procedure will have to use \fBupvar\fR or \fBuplevel\fR if it
wishes to access the traced variable.
Note also that \fIname1\fR may not necessarily be the same as the name
used to set the trace on the variable;  differences can occur if
the access is made through a variable defined with the \fBupvar\fR
command.
.LP
For read and write traces, \fIcommand\fR can modify
the variable to affect the result of the traced operation.
If \fIcommand\fR modifies the value of a variable during a
read or write trace, then the new value will be returned as the
result of the traced operation.
The return value from  \fIcommand\fR is ignored except that
if it returns an error of any sort then the traced operation
is aborted with an error message saying that the access was denied
(this mechanism can be used to implement read-only variables, for
example).
For write traces, \fIcommand\fR is invoked after the variable's
value has been changed; it can write a new value into the variable
to override the original value specified in the write operation.
To implement read-only variables, \fIcommand\fR will have to restore
the old value of the variable.
.LP
While \fIcommand\fR is executing during a read or write trace, traces
on the variable are temporarily disabled.
This means that reads and writes invoked by
\fIcommand\fR will occur directly, without invoking \fIcommand\fR
(or any other traces) again.
.LP
When an unset trace is invoked, the variable has already been
deleted:  it will appear to be undefined with no traces.
If an unset occurs because of a procedure return, then the
trace will be invoked in the variable context of the procedure
being returned to:  the stack frame of the returning procedure
will no longer exist.
Traces are not disabled during unset traces, so if an unset trace
command creates a new trace and accesses the variable, the
trace will be invoked.
.LP
If there are multiple traces on a variable they are invoked
in order of creation, most-recent first.
If one trace returns an error, then no further traces are
invoked for the variable.
If an array element has a trace set, and there is also a trace
set on the array as a whole, the trace on the overall array
is invoked before the one on the element.
.LP
Once created, the trace remains in effect either until the
trace is removed with the \fBtrace vdelete\fR command described
below, until the variable is unset, or until the interpreter
is deleted.
Unsetting an element of array will remove any traces on that
element, but will not remove traces on the overall array.
.LP
This command returns an empty string.
.RE
.TP
\fBtrace vdelete \fIname ops command\fR
If there is a trace set on variable \fIname\fR with the
operations and command given by \fIops\fR and \fIcommand\fR,
then the trace is removed, so that \fIcommand\fR will never
again be invoked.
Returns an empty string.
.TP
\fBtrace vinfo \fIname\fR
Returns a list containing one element for each trace
currently set on variable \fIname\fR.
Each element of the list is itself a list containing two
elements, which are the \fIops\fR and \fIcommand\fR associated
with the trace.
If \fIname\fR doesn't exist or doesn't have any traces set, then
the result of the command will be an empty string.
.RE
.TP
\fBunknown \fIcmdName \fR?\fIarg arg ...\fR?
This command doesn't actually exist as part of Tcl, but Tcl will
invoke it if it does exist.
If the Tcl interpreter encounters a command name for which there
is not a defined command, then Tcl checks for the existence of
a command named \fBunknown\fR.
If there is no such command, then the interpeter returns an
error.
If the \fBunknown\fR command exists, then it is invoked with
arguments consisting of the fully-substituted name and arguments
for the original non-existent command.
The \fBunknown\fR command typically does things like searching
through library directories for a command procedure with the name
\fIcmdName\fR, or expanding abbreviated command names to full-length,
or automatically executing unknown commands as UNIX sub-processes.
In some cases (such as expanding abbreviations) \fBunknown\fR will
change the original command slightly and then (re-)execute it.
The result of the \fBunknown\fR command is used as the result for
the original non-existent command.
.TP
\fBunset \fIname \fR?\fIname name ...\fR?
Remove one or more variables.
Each \fIname\fR is a variable name, specified in any of the
ways acceptable to the \fBset\fR command.
If a \fIname\fR refers to an element of an array, then that
element is removed without affecting the rest of the array.
If a \fIname\fR consists of an array name with no parenthesized
index, then the entire array is deleted.
The \fBunset\fR command returns an empty string as result.
An error occurs if any of the variables doesn't exist.
.VE
.TP
\fBuplevel \fR?\fIlevel\fR?\fI command \fR?\fIcommand ...\fR?
All of the \fIcommand\fR arguments are concatenated as if they had
been passed to \fBconcat\fR; the result is then evaluated in the
variable context indicated by \fIlevel\fR.  \fBUplevel\fR returns
the result of that evaluation.  If \fIlevel\fR is an integer, then
it gives a distance (up the procedure calling stack) to move before
executing the command.  If \fIlevel\fR consists of \fB#\fR followed by
a number then the number gives an absolute level number.  If \fIlevel\fR
is omitted then it defaults to \fB1\fR.  \fILevel\fR cannot be
defaulted if the first \fIcommand\fR argument starts with a digit or \fB#\fR.
For example, suppose that procedure \fBa\fR was invoked
from top-level, and that it called \fBb\fR, and that \fBb\fR called \fBc\fR.
Suppose that \fBc\fR invokes the \fBuplevel\fR command.  If \fIlevel\fR
is \fB1\fR or \fB#2\fR  or omitted, then the command will be executed
in the variable context of \fBb\fR.  If \fIlevel\fR is \fB2\fR or \fB#1\fR
then the command will be executed in the variable context of \fBa\fR.
If \fIlevel\fR is \fB3\fR or \fB#0\fR then the command will be executed
at top-level (only global variables will be visible).
The \fBuplevel\fR command causes the invoking procedure to disappear
from the procedure calling stack while the command is being executed.
In the above example, suppose \fBc\fR invokes the command
.RS
.DS
\fBuplevel 1 {set x 43; d}
.DE
where \fBd\fR is another Tcl procedure.  The \fBset\fR command will
modify the variable \fBx\fR in \fBb\fR's context, and \fBd\fR will execute
at level 3, as if called from \fBb\fR.  If it in turn executes
the command
.DS
\fBuplevel {set x 42}
.DE
then the \fBset\fR command will modify the same variable \fBx\fR in \fBb\fR's
context:  the procedure \fBc\fR does not appear to be on the call stack
when \fBd\fR is executing.  The command ``\fBinfo level\fR'' may
be used to obtain the level of the current procedure.
\fBUplevel\fR makes it possible to implement new control
constructs as Tcl procedures (for example, \fBuplevel\fR could
be used to implement the \fBwhile\fR construct as a Tcl procedure).
.RE
.TP
\fBupvar \fR?\fIlevel\fR? \fIotherVar myVar \fR?\fIotherVar myVar \fR...?
.VS
This command arranges for one or more local variables in the current
procedure to refer to variables in an enclosing procedure call or
to global variables.
\fILevel\fR may have any of the forms permitted for the \fBuplevel\fR
command, and may be omitted if the first letter of the first \fIotherVar\fR
isn't \fB#\fR or a digit (it defaults to \fB1\fR).
For each \fIotherVar\fR argument, \fBupvar\fR makes the variable
by that name in the procedure frame given by \fIlevel\fR (or at
global level, if \fIlevel\fR is \fB#0\fR) accessible
in the current procedure by the name given in the corresponding
\fImyVar\fR argument.
The variable named by \fIotherVar\fR need not exist at the time of the
call;  it will be created the first time \fImyVar\fR is referenced, just like
an ordinary variable.
\fBUpvar\fR may only be invoked from within procedures.
Neither \fIotherVar\fR or \fImyVar\fR may refer to an element of an
array.
\fBUpvar\fR returns an empty string.
.RS
.LP
The \fBupvar\fR command simplifies the implementation of call-by-name
procedure calling and also makes it easier to build new control constructs
as Tcl procedures.
For example, consider the following procedure:
.DS
.ta 1c 2c 3c
\fBproc add2 name {
    upvar $name x
    set x [expr $x+2]
}
.DE
\fBAdd2\fR is invoked with an argument giving the name of a variable,
and it adds two to the value of that variable.
Although \fBadd2\fR could have been implemented using \fBuplevel\fR
instead of \fBupvar\fR, \fBupvar\fR makes it simpler for \fBadd2\fR
to access the variable in the caller's procedure frame.
.VE
.RE
.TP
\fBwhile \fItest body
.VS
The \fIwhile\fR command evaluates \fItest\fR as an expression
(in the same way that \fBexpr\fR evaluates its argument).
The value of the expression must be numeric; if it is non-zero
then \fIbody\fR is executed by passing it to the Tcl interpreter.
Once \fIbody\fR has been executed then \fItest\fR is evaluated
again, and the process repeats until eventually \fItest\fR
evaluates to a zero numeric value.  \fBContinue\fR
commands may be executed inside \fIbody\fR to terminate the current
iteration of the loop, and \fBbreak\fR
commands may be executed inside \fIbody\fR to cause immediate
termination of the \fBwhile\fR command.  The \fBwhile\fR command
always returns an empty string.
.VE

.SH "BUILT-IN VARIABLES"
.PP
The following global variables are created and managed automatically
by the Tcl library.  Except where noted below, these variables should
normally be treated as read-only by application-specific code and by users.
.TP
\fBenv\fR
.br
.VS
This variable is maintained by Tcl as an array
whose elements are the environment variables for the process.
Reading an element will return the value of the corresponding
environment variable.
Setting an element of the array will modify the corresponding
environment variable or create a new one if it doesn't already
exist.
Unsetting an element of \fBenv\fR will remove the corresponding
environment variable.
Changes to the \fBenv\fR array will affect the environment
passed to children by commands like \fBexec\fR.
If the entire \fBenv\fR array is unset then Tcl will stop
monitoring \fBenv\fR accesses and will not update environment
variables.
.TP
\fBerrorCode\fR
After an error has occurred, this variable will be set to hold
additional information about the error in a form that is easy
to process with programs.
\fBerrorCode\fR consists of a Tcl list with one or more elements.
The first element of the list identifies a general class of
errors, and determines the format of the rest of the list.
The following formats for \fBerrorCode\fR are used by the
Tcl core; individual applications may define additional formats.
.RS
.TP
\fBCHILDKILLED\fI pid sigName msg\fR
This format is used when a child process has been killed because of
a signal.  The second element of \fBerrorCode\fR will be the
process's identifier (in decimal).
The third element will be the symbolic name of the signal that caused
the process to terminate; it will be one of the names from the
include file signal.h, such as \fBSIGPIPE\fR.
The fourth element will be a short human-readable message
describing the signal, such as ``write on pipe with no readers''
for \fBSIGPIPE\fR.
.TP
\fBCHILDSTATUS\fI pid code\fR
This format is used when a child process has exited with a non-zero
exit status.  The second element of \fBerrorCode\fR will be the
process's identifier (in decimal) and the third element will be the exit
code returned by the process (also in decimal).
.TP
\fBCHILDSUSP\fI pid sigName msg\fR
This format is used when a child process has been suspended because
of a signal.
The second element of \fBerrorCode\fR will be the process's identifier,
in decimal.
The third element will be the symbolic name of the signal that caused
the process to suspend; this will be one of the names from the
include file signal.h, such as \fBSIGTTIN\fR.
The fourth element will be a short human-readable message
describing the signal, such as ``background tty read''
for \fBSIGTTIN\fR.
.TP
\fBNONE\fR
.br
This format is used for errors where no additional information is
available for an error besides the message returned with the
error.  In these cases \fBerrorCode\fR will consist of a list
containing a single element whose contents are \fBNONE\fR.
.TP
\fBUNIX \fIerrName msg\fR
If the first element of \fBerrorCode\fR is \fBUNIX\fR, then
the error occurred during a UNIX kernel call.
The second element of the list will contain the symbolic name
of the error that occurred, such as \fBENOENT\fR; this will
be one of the values defined in the include file errno.h.
The third element of the list will be a human-readable
message corresponding to \fIerrName\fR, such as
``no such file or directory'' for the \fBENOENT\fR case.
.PP
To set \fBerrorCode\fR, applications should use library
procedures such as \fBTcl_SetErrorCode\fR and
\fBTcl_UnixError\fR, or they may invoke the \fBerror\fR command.
If one of these methods hasn't been used, then the Tcl
interpreter will reset the variable to \fBNONE\fR after
the next error.
.RE
.VE
.TP
\fBerrorInfo\fR
After an error has occurred, this string will contain one or more lines
identifying the Tcl commands and procedures that were being executed
when the most recent error occurred.
Its contents take the form of a stack trace showing the various
nested Tcl commands that had been invoked at the time of the error.

.SH AUTHOR
John Ousterhout, University of California at Berkeley ([e-mail])
.sp
Many people have contributed to Tcl in various ways, but the following
people have made unusually large contributions:
.sp
.nf
Bill Carpenter
Peter Da Silva
Mark Diekhans
Karl Lehenbauer
Mary Ann May-Pumphrey