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SH(1L)
NAME
sh, rsh - shell, the standard/restricted command programming
language
SYNOPSIS
sh [ -acefhiknmrstuvx ] [ args ]
rsh [ -acefhiknmrstuvx ] [ args ]
DESCRIPTION
_S_h is a command programming language that executes commands
read from a terminal or a file. _R_s_h is a restricted version
of the standard command interpreter _s_h; it is used to set up
login names and execution environments whose capabilities
are more controlled than those of the standard shell. See
_I_n_v_o_c_a_t_i_o_n below for the meaning of arguments to the shell.
Definitions
A _b_l_a_n_k is a tab or a space. A _n_a_m_e is a sequence of
letters, digits, or underscores beginning with a letter or
underscore. A _p_a_r_a_m_e_t_e_r is a name, a digit, or any of the
characters *, @, #, ?, -, $, and !.
Commands
A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of non-blank _w_o_r_d_s separated
by _b_l_a_n_k_s. The first word specifies the name of the command
to be executed. Except as specified below, the remaining
words are passed as arguments to the invoked command. The
command name is passed as argument 0 (see _e_x_e_c(2)). The
_v_a_l_u_e of a simple-command is its exit status if it ter-
minates normally, or (octal) 200+_s_t_a_t_u_s if it terminates
abnormally (see _s_i_g_n_a_l(2) for a list of status values).
A _p_i_p_e_l_i_n_e is a sequence of one or more _c_o_m_m_a_n_d_s separated
by | (or, for historical compatibility, by ^). The standard
output of each command but the last is connected by a
_p_i_p_e(2) to the standard input of the next command. Each
command is run as a separate process; the shell waits for
the last command to terminate. The exit status of a pipe-
line is the exit status of the last command.
A _l_i_s_t is a sequence of one or more pipelines separated by
;, &&, or ||, and optionally terminated by ;. Of these
three symbols, ; has a lower precedence than that of && and
||. The symbols && and || also have equal precedence. A
semicolon (;) causes sequential execution of the preceding
pipeline. The symbol && (||) causes the _l_i_s_t following it
to be executed only if the preceding pipeline returns a zero
(non-zero) exit status. An arbitrary number of new-lines
may appear in a _l_i_s_t, instead of semicolons, to delimit com-
mands.
1
SH(1L)
A _c_o_m_m_a_n_d is either a simple-command or one of the follow-
ing. Unless otherwise stated, the value returned by a com-
mand is that of the last simple-command executed in the com-
mand.
for _n_a_m_e [ in _w_o_r_d ... ] do _l_i_s_t done
Each time a for command is executed, _n_a_m_e is set to the
next _w_o_r_d taken from the in _w_o_r_d list. If in _w_o_r_d ...
is omitted, then the for command executes the do _l_i_s_t
once for each positional parameter that is set (see
_P_a_r_a_m_e_t_e_r _S_u_b_s_t_i_t_u_t_i_o_n below). Execution ends when
there are no more words in the list.
case _w_o_r_d in [ _p_a_t_t_e_r_n [ | _p_a_t_t_e_r_n ] ... ) _l_i_s_t ;; ] ... esac
A case command executes the _l_i_s_t associated with the
first _p_a_t_t_e_r_n that matches _w_o_r_d. The form of the pat-
terns is the same as that used for file-name generation
(see _F_i_l_e _N_a_m_e _G_e_n_e_r_a_t_i_o_n) except that a slash, a lead-
ing dot, or a dot immediately following a slash need
not be matched explicitly, and the match is case sensi-
tive.
if _l_i_s_t then _l_i_s_t [ elif _l_i_s_t then _l_i_s_t ] ... [ else _l_i_s_t ] fi
The _l_i_s_t following if is executed and, if it returns a
zero exit status, the _l_i_s_t following the first then is
executed. Otherwise, the _l_i_s_t following elif is exe-
cuted and, if its value is zero, the _l_i_s_t following the
next then is executed. Failing that, the else _l_i_s_t is
executed. If no else _l_i_s_t or then _l_i_s_t is executed,
then the if command returns a zero exit status.
while _l_i_s_t do _l_i_s_t done
A while command repeatedly executes the while _l_i_s_t and,
if the exit status of the last command in the list is
zero, executes the do _l_i_s_t; otherwise the loop ter-
minates. If no commands in the do _l_i_s_t are executed,
then the while command returns a zero exit status;
until may be used in place of while to negate the loop
termination test.
(_l_i_s_t)
Execute _l_i_s_t in a sub-shell. The shell creates a new
environment in which to execute the _l_i_s_t, but does not
fork a sub-shell as a Unix system would. The original
environment is restored on completion.
{_l_i_s_t;}
_l_i_s_t is simply executed.
_n_a_m_e () {_l_i_s_t;}
Define a function which is referenced by _n_a_m_e. The
body of the function is the _l_i_s_t of commands between {
and }. Execution of functions is described below (see
_E_x_e_c_u_t_i_o_n).
The following words are only recognized as the first word of
a command and when not quoted:
2
SH(1L)
if then else elif fi case esac for while until do done { }
Comments
A word beginning with # causes that word and all the follow-
ing characters up to a new-line to be ignored.
Command Substitution
The standard output from a command enclosed in a pair of
grave accents (``) may be used as part or all of a word;
trailing new-lines are removed.
Parameter Substitution
The character $ is used to introduce substitutable _p_a_r_a_m_e_-
_t_e_r_s. There are two types of parameters, positional and
keyword. If _p_a_r_a_m_e_t_e_r is a digit, it is a positional param-
eter. Positional parameters may be assigned values by set.
Keyword parameters (also known as variables) may be assigned
values by writing:
_n_a_m_e = _v_a_l_u_e [ _n_a_m_e = _v_a_l_u_e ] ...
Pattern-matching is not performed on _v_a_l_u_e. There cannot be
a function and a variable with the same _n_a_m_e.
${_p_a_r_a_m_e_t_e_r}
The value, if any, of the parameter is substituted.
The braces are required only when _p_a_r_a_m_e_t_e_r is followed
by a letter, digit, or underscore that is not to be
interpreted as part of its name. If _p_a_r_a_m_e_t_e_r is * or
@, all the positional parameters, starting with $1, are
substituted (separated by spaces). Parameter $0 is set
from argument zero when the shell is invoked.
${_p_a_r_a_m_e_t_e_r:-_w_o_r_d}
If _p_a_r_a_m_e_t_e_r is set and is non-null, substitute its
value; otherwise substitute _w_o_r_d.
${_p_a_r_a_m_e_t_e_r:=_w_o_r_d}
If _p_a_r_a_m_e_t_e_r is not set or is null set it to _w_o_r_d; the
value of the parameter is substituted. Positional
parameters may not be assigned to in this way.
${_p_a_r_a_m_e_t_e_r:?_w_o_r_d}
If _p_a_r_a_m_e_t_e_r is set and is non-null, substitute its
value; otherwise, print _w_o_r_d and exit from the shell.
If _w_o_r_d is omitted, the message ``parameter null or not
set'' is printed.
${_p_a_r_a_m_e_t_e_r:+_w_o_r_d}
If _p_a_r_a_m_e_t_e_r is set and is non-null, substitute _w_o_r_d;
otherwise substitute nothing.
In the above, _w_o_r_d is not evaluated unless it is to be used
as the substituted string, so that, in the following exam-
ple, pwd is executed only if d is not set or is null:
3
SH(1L)
echo ${d:-`pwd`}
If the colon (:) is omitted from the above expressions, the
shell only checks whether _p_a_r_a_m_e_t_e_r is set or not (_I_t _i_s _n_o_t
_c_l_e_a_r _w_h_a_t _t_h_i_s _m_e_a_n_s).
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- Flags supplied to the shell on invocation or by the
set command.
? The decimal value returned by the last synchronously
executed command.
$ The process number of this shell.
! The process number of the last background command
invoked.
~ The shell reserves all variables beginning with a ~
for its own internal use and these variables cannot
be accessed by the user.
The following parameters are used by the shell:
CDPATH
The search path for the _c_d command. (Note that
becuase a colon is used by MSDOS to indicate a drive,
a semi-colon is used to separate the path names
instead of a colon - this implies that the CDPATH
variable must be set using single or double quotes to
surround the value).
EXTENDED_LINE
This parameter defines a file containing a list of
command which can accept an Extended Command Line
using the indirect command file character @. When a
command which can process the Extended Command Line
finds a parameter starting with a @ in the command
list, treats the rest of the parameter as a file and
reads the parameters from that file. Examples of
this functionality include the Standard Linker and
Librarian. The filename defined by EXTENDED_LINE
contains a list of command (including the .exe or
.com extension) separated by a newlines. If the
command is in upper case, the file name on the com-
mand line is set up with backslashes as the directory
separator. Otherwise, slashes (Unix style) are used.
This functionality allows the user to get round the
127 byte command line length limit of MSDOS.
HISTFILE
The file where command history is saved across login
sessions. The default value is $HOME/history.sh.
HOME
The default argument (home directory) for the _c_d com-
mand.
IFS
Internal field separators, normally space, tab, and
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SH(1L)
new-line.
MAIL
If this parameter is set to the name of a mail file
_a_n_d the MAILPATH parameter is not set, the shell
informs the user of the arrival of mail in the speci-
fied file.
MAILCHECK
This parameter specifies how often (in seconds) the
shell will check for the arrival of mail in the files
specified by the MAILPATH or MAIL parameters. If set
to 0, the shell will check before each prompt.
MAILPATH
A colon (:) separated list of file names. If this
parameter is set, the shell informs the user of the
arrival of mail in any of the specified files. Each
file name can be followed by % and a message that
will be printed when the modification time changes.
The default message is "_y_o_u _h_a_v_e _m_a_i_l".
PATH
The search path for commands (see _E_x_e_c_u_t_i_o_n below).
The user may not change PATH if executing under _r_s_h.
(Note that because a colon is used by MSDOS to indi-
cate a drive, a semi-colon is used to separate the
path names instead of a colon - this implies that the
PATH variable must be set using single or double
quotes to surround the value).
PS1
Primary prompt string, by default ``$ ''.
PS2
Secondary prompt string, by default ``> ''.
SHELL
When the shell is invoked, it scans the environment
(see _E_n_v_i_r_o_n_m_e_n_t below) for this name. If it is
found and there is an 'r' in the file name part of
its value, the shell becomes a restricted shell.
TMP
The location of temporary files created by the shell.
The shell gives default values to PATH, PS1, PS2, SHELL,
HOME and IFS.
Blank Interpretation
After parameter and command substitution, the results of
substitution are scanned for internal field separator char-
acters (those found in IFS) and split into distinct argu-
ments where such characters are found. Explicit null argu-
ments ("" or '') are retained. Implicit null arguments
(those resulting from _p_a_r_a_m_e_t_e_r_s that have no values) are
removed.
File Name Generation
Following substitution, each command _w_o_r_d is scanned for the
characters *, ? and [. If one of these characters appears
the word is regarded as a _p_a_t_t_e_r_n. The word is replaced
with alphabetically sorted file names that match the
5
SH(1L)
pattern. If no file name is found that matches the pattern,
the word is left unchanged. The character . at the start of
a file name or immediately following a /, as well as the
character / itself, must be matched explicitly. When match-
ing patterns for file names, the shell ignores the case of
the pattern and the file directory entries. Generated file
names are always in lower case.
* Matches any string, including the null string.
? Matches any single character.
[ ... ]
Matches any one of the enclosed characters. A pair
of characters separated by - matches any character
lexically between the pair, inclusive. If the first
character following the opening ``['' is a ``!'' any
character not enclosed is matched.
Quoting
The following characters have a special meaning to the shell
and cause termination of a word unless quoted:
; & ( ) | ^ < > new-line space tab
A character may be _q_u_o_t_e_d (i.e., made to stand for itself)
by preceding it with a \. The pair \new-line is ignored.
All characters enclosed between a pair of single quote marks
(''), except a single quote, are quoted. Inside double
quote marks (""), parameter and command substitution occurs
and \ quotes the characters \, `, ", and $. "$*" is
equivalent to "$1 $2 ...", whereas "$@" is equivalent to
"$1" "$2" ....
Prompting
When used interactively, the shell prompts with the value of
PS1 before reading a command. If at any time a new-line is
typed and further input is needed to complete a command, the
secondary prompt (i.e., the value of PS2) is issued.
Many people like to have the shell provide them with useful
information in their prompt. To accommodate this, the shell
recognises special sequences of characters in the values of
PS1 and PS2, and substitutes the appropriate information for
them. The special sequences and what they signify are:
%dPlace the current date, in the form DAY DD-MM-YY into
the prompt.
%ePlace the current event number (as defined by the
history command) into the prompt. If history evalua-
tion has been turned off (via history -d), no number
will be substituted in (i.e. the %e will be removed).
%nPlace the current working drive into the prompt.
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SH(1L)
%pPlace the current working directory into the prompt.
%tPlace the current time of day, in the form HH:MM into
the prompt. The time is on a 24 hour clock, i.e.
1:30 in the afternoon will be 13:30.
%vPlace the MSDOS version number, in the form MSDOS
MM:MM into the prompt.
%%Place the character % into the prompt.
\xxx
Place the character _\_x_x_x into the prompt. The pro-
cessing of escape sequences is the same as that for
echo.
Some of these facilities are of more use than others.
Input/Output
Before a command is executed, its input and output may be
redirected using a special notation interpreted by the
shell. The following may appear anywhere in a simple-
command or may precede or follow a _c_o_m_m_a_n_d and are _n_o_t
passed on to the invoked command; substitution occurs before
_w_o_r_d or _d_i_g_i_t is used:
<word Use file _w_o_r_d as standard input (file descrip-
tor 0).
>word Use file _w_o_r_d as standard output (file
descriptor 1). If the file does not exist it
is created; otherwise, it is truncated to zero
length.
>>word Use file _w_o_r_d as standard output. If the file
exists output is appended to it (by first
seeking to the end-of-file); otherwise, the
file is created.
<<[-]word The shell input is read up to a line that is
the same as _w_o_r_d, or to an end-of-file. The
resulting document becomes the standard input.
If any character of _w_o_r_d is quoted, no
interpretation is placed upon the characters
of the document; otherwise, parameter and com-
mand substitution occurs, (unescaped) \new-
line is ignored, and \ must be used to quote
the characters \, $, `, and the first charac-
ter of _w_o_r_d. If - is appended to <<, all
leading tabs are stripped from _w_o_r_d and from
the document.
<&digit Use the file associated with file descriptor
_d_i_g_i_t as standard input. Similarly for the
standard output using >&digit.
<&- The standard input is closed. Similarly for
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SH(1L)
the standard output using >&-.
If any of the above is preceded by a digit, the file
descriptor which will be associated with the file is that
specified by the digit (instead of the default 0 or 1). For
example:
... 2>&1
associates file descriptor 2 with the file currently associ-
ated with file descriptor 1.
The order in which redirections are specified is signifi-
cant. The shell evaluates redirections left-to-right. For
example:
... 1>_x_x_x 2>&1
first associates file descriptor 1 with file _x_x_x. It asso-
ciates file descriptor 2 with the file associated with file
descriptor 1 (i.e. _x_x_x). If the order of redirections were
reversed, file descriptor 2 would be associated with the
terminal (assuming file descriptor 1 had been) and file
descriptor 1 would be associated with file _x_x_x .
The environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.
Redirection of output is not allowed in the restricted
shell.
Environment
The _e_n_v_i_r_o_n_m_e_n_t (see _e_n_v_i_r_o_n(5)) is a list of name-value
pairs that is passed to an executed program in the same way
as a normal argument list. The shell interacts with the
environment in several ways. On invocation, the shell scans
the environment and creates a parameter for each name found,
giving it the corresponding value. If the user modifies the
value of any of these parameters or creates new parameters,
none of these affects the environment unless the export com-
mand is used to bind the shell's parameter to the environ-
ment (see also set -a). A parameter may be removed from the
environment with the unset command. The environment seen by
any executed command is thus composed of any unmodified
name-value pairs originally inherited by the shell, minus
any pairs removed by unset, plus any modifications or addi-
tions, all of which must be noted in export commands.
The environment for any _s_i_m_p_l_e-_c_o_m_m_a_n_d may be augmented by
prefixing it with one or more assignments to parameters.
Thus:
8
SH(1L)
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the execution of _c_m_d is con-
cerned).
If the -k flag is set, _a_l_l keyword arguments are placed in
the environment, even if they occur after the command name.
The following first prints a=b c and c:
echo a=b c
set -k
echo a=b c
Signals
The INTERRUPT and QUIT signals for an invoked command are
ignored if the command is followed by &; otherwise signals
have the values inherited by the shell from its parent, with
the exception of signal 11 (but see also the trap command
below).
History
When reading input from an interactive terminal, a ``!'' at
the start of a line signals to the shell that it should
attempt to perform a history subsitution. A history subsi-
tution is a short-hand method which allows the user to
recall a previous command for execution or editing. The
recalled command is placed in the command line for editing
or passing to the rest of the shell for normal processing.
A history substitution takes the form:
! [ _s_t_r | _n_u_m ] _t_e_r_m_i_n_a_t_o_r
!_n_u_m will place the history command with the specified
number in the command line. !_s_t_r will find the most recent
command line that started with the characters in _s_t_r.
The _t_e_r_m_i_n_a_t_o_r determines what action is performed after the
history line has been found. If the original history com-
mand is entered using the <return> key, the new command line
is passed directly to the shell. If the <end> key is
pressed, the new command line can be edited in the manner
described below.
Command Line Editing
When reading input from an interactive terminal, certain
keystrokes allow the current input line to be edited. The
following keystrokes are available:
Cursor Right
Move the cursor right one character
9
SH(1L)
Control-Cursor Right
Move the cursor right one word
Cursor Left
Move the cursor left one character
Control-Cursor Left
Move the cursor left one word
Cursor Up
Get the previous command from the history file
Cursor Down
Get the next command from the history file
Insert
Toggle insert/overwrite mode
Delete
Delete the current character
Home Move the cursor to the start of the command
End Move the cursor to the end of the command, unless the
first character of the command is a !, in which case
the appropriate history search is done.
Control-End
Delete to the end of the line
Page-Up
Search backwards from the current history command for
the next match against the last history request. This
command can only be used after End has been used to
select a history line.
Page-Down
Search forewards from the current history command for
the next match against the last history request. This
command can only be used after End has been used to
select a history line.
Backspace
Move the cursor back one character, erasing the current
character.
Return
Execute the command line, unless the first character of
the command is a !, in which case the appropriate his-
tory processing is done.
10
SH(1L)
Execution
Each time a command is executed, the above substitutions are
carried out. If the command name matches one of the _S_p_e_c_i_a_l
_C_o_m_m_a_n_d_s listed below, it is executed in the shell process.
If the command name does not match a _S_p_e_c_i_a_l _C_o_m_m_a_n_d, but
matches the name of a defined function, the function is exe-
cuted in the shell process (note how this differs from the
execution of shell procedures). The positional parameters
$1, $2, .... are set to the arguments of the function. If
the command name matches neither a _S_p_e_c_i_a_l _C_o_m_m_a_n_d nor the
name of a defined function, a new process is created and an
attempt is made to execute the command via _e_x_e_c(2).
The shell parameter PATH defines the search path for the
directory containing the command. Alternative directory
names are separated by a semi-colon (;). The default path
is ;c:/bin;c:/usr/bin (specifying the current directory,
c:/bin, and c:/usr/bin, in that order). Note that the
current directory is specified by a null path name, which
can appear immediately after the equal sign or between the
semi-colon delimiters anywhere else in the path list. If
the command name contains a / or starts with x: (where x is
a drive letter) the search path is not used; such commands
will not be executed by the restricted shell. Otherwise,
each directory in the path is searched for an executable
file.
If the file does not have a .com or .exe extension, it is
opened and the first 5 characters are read. If the first 5
characters are the string #!sh\n it is assumed to be a file
containing shell commands. Note that the shell will check
the file and if that file does not exist or is not a script,
it will try the file with an extension of .sh. If a .sh
file is found, that will be processed. A sub-shell is
spawned to read it. A parenthesized command is also exe-
cuted in a sub-shell.
Special Commands
Input/output redirection is permitted for these commands.
File descriptor 1 is the default output location.
: No effect; the command does nothing. A zero exit code
is returned.
_l_e_t_t_e_r:
Select the drive specified by _l_e_t_t_e_r.
. _f_i_l_e
Read and execute commands from _f_i_l_e and return. The
search path specified by PATH is used to find the
directory containing _f_i_l_e.
break [ _n ]
Exit from the enclosing for or while loop, if any. If
_n is specified, break _n levels.
11
SH(1L)
continue [ _n ]
Resume the next iteration of the enclosing for or while
loop. If _n is specified, resume at the _n-th enclosing
loop.
cd [ _a_r_g ]
Change the current directory to _a_r_g. The shell parame-
ter HOME is the default _a_r_g. The shell parameter
CDPATH defines the search path for the directory con-
taining _a_r_g. Alternative directory names are separated
by a semi-colon (;). The default path is <null>
(specifying the current directory). Note that the
current directory is specified by a null path name,
which can appear immediately after the equal sign or
between the semi-colon delimiters anywhere else in the
path list. If _a_r_g begins with a / or x: (where x is a
drive letter), the search path is not used. Otherwise,
each directory in the path is searched for _a_r_g. The _c_d
command may not be executed by _r_s_h.
echo [ _a_r_g ... ]
Echo arguments. Echo writes its arguments separated by
blanks and terminated by a new-line on the standard
output. It also understands C-like escape conventions;
beware of conflicts with the shell's use of \:
\bbackspace
\cprint line without new-line
\fform-feed
\nnew-line
\rcarriage return
\ttab
\vvertical tab
\\backslash
\_nthe 8-bit character whose ASCII code is the 1-, 2- or
3-digit octal number _n, which must start with a zero.
_E_c_h_o is useful for producing diagnostics in command
files and for sending known data into a pipe.
eval [ _a_r_g ... ]
The arguments are read as input to the shell and the
resulting command(s) executed.
exec [ _a_r_g ... ]
The command specified by the arguments is executed in
place of this shell without creating a new process.
Input/output arguments may appear and, if no other
arguments are given, cause the shell input/output to be
modified.
exit [ _n ]
Causes a shell to exit with the exit status specified
by _n. If _n is omitted the exit status is that of the
last command executed (an end-of-file will also cause
12
SH(1L)
the shell to exit.)
export [ _n_a_m_e ... ]
The given _n_a_m_es are marked for automatic export to the
_e_n_v_i_r_o_n_m_e_n_t of subsequently-executed commands. If no
arguments are given, a list of all names that are
exported in this shell is printed. Function names may
_n_o_t be exported.
getopt _o_p_t_s_t_r_i_n_g _n_a_m_e [ _a_r_g_s ... ]
Parse command options and write them to standard out-
put. Getopt is used to break up options in command
lines for easy parsing by shell procedures and to check
for legal options. _O_p_t_s_t_r_i_n_g is a string of recognized
option letters (see _g_e_t_o_p_t(3C)); if a letter is fol-
lowed by a colon, the option is expected to have an
argument which may or may not be separated from it by
white space. The special option -- is used to delimit
the end of the options. If it is used explicitly,
getopt will recognize it; otherwise, getopt will gen-
erate it; in either case, getopt will place it at the
end of the options. Each option is preceded by a - and
is in its own positional parameter; each option argu-
ment is also parsed into its own positional parameter.
The following code fragment shows how one might process
the arguments for a command that can take the options a
or b, as well as the option o, which requires an argu-
ment:
set -- `getopt abo: $*`
if [ $? != 0 ]
then
echo $USAGE
exit 2
fi
for i in $*
do
case $i in
-a | -b) FLAG=$i; shift;;
-o) OARG=$2; shift 2;;
--) shift; break;;
esac
done
This code will accept any of the following as
equivalent:
cmd -aoarg file file
cmd -a -o arg file file
cmd -oarg -a file file
cmd -a -oarg -- file file
13
SH(1L)
history [ -dei ]
The history command, with no arguments, will print all
the commands that are currently saved in the shell's
history buffers. As new commands are executed, and
space in the buffers runs out, old commands will be
deleted. The history commands prints out the stored
commands with sequence numbers. Negative numbered com-
mands, through command number zero, are commands that
were retrieved from the saved history file. Commands
starting at one were entered during the current login
session. If a saved command contains embedded new-
lines, these will be printed out as the sequence \n, so
that individual command stay on one line.
The arguments changes the way the shell processes his-
tory information as follows:
-dDisable the saving of commands in the history file.
-eEnable the saving of commands in the history file.
-iInitialise the history file.
msdos [ _n_a_m_e ... ]
The given _n_a_m_es are marked _m_s_d_o_s format and if the -m
flag is set, the values of the these _n_a_m_es are exported
to child processes with the any slashes in the value
replaced by backslashes.
pwd Print the current working directory.
read [ _n_a_m_e ... ]
One line is read from the standard input and the first
word is assigned to the first _n_a_m_e, the second word to
the second _n_a_m_e, etc., with leftover words assigned to
the last _n_a_m_e. The return code is 0 unless an end-of-
file is encountered.
readonly [ _n_a_m_e ... ]
The given _n_a_m_es are marked _r_e_a_d_o_n_l_y and the values of
the these _n_a_m_es may not be changed by subsequent
assignment. If no arguments are given, a list of all
_r_e_a_d_o_n_l_y names is printed.
return [ _n ]
Causes a function to exit with the return value speci-
fied by _n. If _n is omitted, the return status is that
of the last command executed.
set [ --aefkmntuvx [ _a_r_g ... ] ]
-aMark variables which are modified or created for
14
SH(1L)
export.
-eExit immediately if a command exits with a non-zero
exit status.
-fDisable file name generation
-kAll keyword arguments are placed in the environment
for a command, not just those that precede the com-
mand name.
-mFor those variables marked as msdos variables, the
values are exported to child processes with the
slashes replaced by backslashes. Most MSDOS utili-
ties do not care if a file name contains a slash or
backslash as a directory separator. However, some
like the _l_i_n_k_e_r require backslashes in the value of
the LIB variable.
-nRead commands but do not execute them.
-tExit after reading and executing one command.
-uTreat unset variables as an error when substituting.
-vPrint shell input lines as they are read.
-xPrint commands and their arguments as they are exe-
cuted.
--Do not change any of the flags; useful in setting $1
to -.
Using + rather than - causes these flags to be turned
off. These flags can also be used upon invocation of
the shell. The current set of flags may be found in
$-. The remaining arguments are positional parameters
and are assigned, in order, to $1, $2, .... If no
arguments are given the values of all names are
printed.
shift [ _n ]
The positional parameters from $n+1 ... are renamed $1
.... If _n is not given, it is assumed to be 1.
swap [ _o_p_t_i_o_n_s ]
This command defines how the shell will handle swap-
ping. The options are
off
Disable swapping. The shell remains in memory whilst
the child is running and reduces the available memory
15
SH(1L)
by about 200K (depending on the size of the environ-
ment and history).
onEnable all devices. The shell will swap out to
either expanded or extended memory or to disk, exe-
cute the command and then swap back in. Whilest
swapped, the shell reduces the available memory by
about 3K.
expand
Enable swapping to Expanded Memory. The EMS drive
must exist on your system for this to work.
extent [ _s_t_a_r_t _a_d_d_r_e_s_s ]
Enable swapping to Extended Memory. The optional
start address defines the based address in the
Extended Memory at which point the shell writes its
swap area. The default location is _0_x_1_0_0_0_0_0.
disk
Enable swapping to disk. The shell creates a tem-
porary file and saves itself in it. On completion,
the file is deleted. This is the slowest method of
swapping.
With no options, the current swapping options are
displayed.
test _e_x_p_r or [ _e_x_p_r ]
Evaluate conditional expressions. Test evaluates the
expression _e_x_p_r and, if its value is true, returns a
zero (true) exit status; otherwise, a non-zero (false)
exit status is returned; test also returns a non-zero
exit status if there are no arguments. The following
primitives are used to construct expr:
-r _f_i_l_e true if _f_i_l_e exists and is readable.
-w _f_i_l_e true if _f_i_l_e exists and is writable.
-x _f_i_l_e true if _f_i_l_e exists and is executable.
-f _f_i_l_e true if _f_i_l_e exists and is a regular file.
-d _f_i_l_e true if _f_i_l_e exists and is a directory.
-c _f_i_l_e true if _f_i_l_e exists and is a character spe-
cial file.
-b _f_i_l_e true if _f_i_l_e exists and is a block special
file.
16
SH(1L)
-s _f_i_l_e true if _f_i_l_e exists and has a size greater
than zero.
-t [ _f_i_l_d_e_s ]
true if the open file whose file descriptor
number is _f_i_l_d_e_s (1 by default) is associ-
ated with a terminal device.
-n _s_1 true if the length of the string _s_1 is
zero.
-n _s_1 true if the length of the string _s_1 is
non-zero.
_s_1 = _s_2 true if strings _s_1 and _s_2 are identical.
_s_1 != _s_2 true if strings _s_1 and _s_2 are _n_o_t identi-
cal.
_s_1 true if _s_1 is _n_o_t the null string.
_n_1 -eq _n_2 true if the integers _n_1 and _n_2 are algebra-
ically equal. Any of the comparisons -ne,
-gt, -ge, -lt, and -le may be used in place
of R-eq.
These primaries may be combined with the following
operators:
! unary negation operator.
-a binary _a_n_d operator.
-o binary _o_r operator (-a has higher pre-
cedence than -o).
( expr ) parentheses for grouping.
Notice that all the operators and flags are separate
arguments to test. Notice also that parentheses are
meaningful to the shell and, therefore, must be
escaped.
trap [ _a_r_g ] [ _n ] ...
The command _a_r_g is to be read and executed when the
shell receives signal(s) _n. (Note that _a_r_g is scanned
once when the trap is set and once when the trap is
taken.) Trap commands are executed in order of signal
number. Any attempt to set a trap on a signal that was
ignored on entry to the current shell is ineffective.
An attempt to trap on signal 11 (memory fault) produces
an error. If _a_r_g is absent all trap(s) _n are reset to
17
SH(1L)
their original values. If _a_r_g is the null string this
signal is ignored by the shell and by the commands it
invokes. If _n is 0 the command _a_r_g is executed on exit
from the shell. The trap command with no arguments
prints a list of commands associated with each signal
number.
type [ _n_a_m_e ... ]
For each _n_a_m_e, indicate how it would be interpreted if
used as a command name.
umask [ _n_n_n ]
The user file-creation mask is set to _n_n_n (see
_u_m_a_s_k(2)). If _n_n_n is omitted, the current value of the
mask is printed.
unset [ _n_a_m_e ... ]
For each _n_a_m_e, remove the corresponding variable or
function. The variables PATH, PS1, PS2, and IFS cannot
be unset.
ver Display the current version of the shell.
Invocation
If the shell is invoked through _e_x_e_c(2) and the first char-
acter of argument zero is - or the -0(zero) switch is in the
invokation line, commands are initially read from
/etc/profile.sh and from $HOME/profile.sh, if such files
exist. Thereafter, commands are read as described below,
which is also the case when the shell is invoked as /bin/sh.
The flags below are interpreted by the shell on invocation
only; Note that unless the -c or -s flag is specified, the
first argument is assumed to be the name of a file contain-
ing commands, and the remaining arguments are passed as
positional parameters to that command file:
-c string If the -c flag is present commands are read from
_s_t_r_i_n_g.
-s If the -s flag is present or if no arguments
remain commands are read from the standard input.
Any remaining arguments specify the positional
parameters. Shell output (except for _S_p_e_c_i_a_l _C_o_m_-
_m_a_n_d_s) is written to file descriptor 2.
-i If the -i flag is present or if the shell input
and output are attached to a terminal, this shell
is _i_n_t_e_r_a_c_t_i_v_e. In this case, the TERMINATE sig-
nal is ignored and the INTERRUPT signal is caught
and ignored. In all cases, the QUIT signal is
ignored by the shell.
-r If the -r flag is present, the shell is a res-
tricted shell.
-0(zero) If the -0(zero) flag is present, this has the same
18
SH(1L)
effect as starting the shell with the first char-
acter of argument zero as a - (see above).
The remaining flags and arguments are described under the
set command above.
Rsh Only
_R_s_h is used to set up login names and execution environments
whose capabilities are more controlled than those of the
standard shell. The actions of _r_s_h are identical to those
of _s_h, except that the following are disallowed:
changing directory (see _c_d(1)),
setting the value of $PATH
specifying path or command names containing /,
redirecting output (> and >>).
The restrictions above are enforced after profile.sh is
interpreted.
When a command to be executed is found to be a shell pro-
cedure, _r_s_h invokes _s_h to execute it. Thus, it is possible
to provide to the end-user shell procedures that have access
to the full power of the standard shell, while imposing a
limited menu of commands; this scheme assumes that the end-
user does not have write and execute permissions in the same
directory.
The net effect of these rules is that the writer of the
profile.sh has complete control over user actions, by per-
forming guaranteed setup actions and leaving the user in an
appropriate directory (probably _n_o_t the login directory).
The system administrator often sets up a directory of com-
mands (i.e., /usr/rbin) that can be safely invoked by _r_s_h.
Some systems also provide a restricted editor _r_e_d.
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause
the shell to return a non-zero exit status. If the shell is
being used non-interactively execution of the shell file is
abandoned. Otherwise, the shell returns the exit status of
the last command executed (see also the exit command above).
FILES
/etc/profile.sh
$HOME/profile.sh
$TMP/sh*
LIMIITATIONS
Any TSR (Terminate Stay Resident) programs must be loaded
before loading _S_h as the shell will overwrite the TSR when
it reloads itself after swapping out.
19
SH(1L)
SEE ALSO
cd(1), env(1), test(1), umask(1).
dup(2), exec(2), pipe(2), signal(2), umask(2), wait(2), pro-
file(4), environ(5) in the _U_N_I_X _S_y_s_t_e_m _P_r_o_g_r_a_m_m_e_r _R_e_f_e_r_e_n_c_e
_M_a_n_u_a_l.
20
