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sh(C) 06 January 1993 sh(C)
_N_a_m_e
sh - invoke the shell command interpreter
_S_y_n_t_a_x
sshh [ --aacceeiikknnrrssttuuvvxx ] [ _aa_rr_gg_ss ]
_D_e_s_c_r_i_p_t_i_o_n
The shell is the standard command programming language that executes com-
mands read from a terminal or a file. See ``Invocation'' below for the
meaning of arguments to the shell.
_C_o_m_m_a_n_d_s
A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of nonblank _w_o_r_d_s separated by _b_l_a_n_k_s (a
_b_l_a_n_k is a tab or a space). 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 eexxeecc(S)). The _v_a_l_u_e of a simple-command is its
exit status if it terminates normally, or (octal) 1000+_ss_tt_aa_tt_uu_ss if it ter-
minates abnormally. See ssiiggnnaall(S) 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 a vertical
bar (||). (The caret (^^), is an obsolete synonym for the vertical bar and
should not be used in a pipeline. Scripts that use ``^'' for pipelines
are incompatible with the Korn shell.) The standard output of each com-
mand but the last is connected by a ppiippee(S) 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.
A _l_i_s_t is a sequence of one or more pipelines separated by ;;, &&, &&&&, or
||||, and optionally terminated by ;; or &&. Of these four symbols, ;; and &&
have equal precedence, which is lower than that of &&&& and ||||. The sym-
bols &&&& and |||| also have equal precedence. A semicolon (;;) causes
sequential execution of the preceding pipeline; an ampersand (&&) causes
asynchronous execution of the preceding pipeline (that is, the shell does
_n_o_t wait for that pipeline to finish). The symbol &&&& (||||) causes the
_l_i_s_t following it to be executed only if the preceding pipeline returns a
zero (nonzero) exit status. An arbitrary number of newlines may appear
in a _l_i_s_t, instead of semicolons, to delimit commands.
A _c_o_m_m_a_n_d is either a simple-command or one of the following commands.
Unless otherwise stated, the value returned by a command is that of the
last simple-command executed in the command:
ffoorr _nn_aa_mm_ee [ iinn _ww_oo_rr_dd ... ]
ddoo
_ll_ii_ss_tt
ddoonnee
Each time a ffoorr command is executed, _nn_aa_mm_ee is set to the next _ww_oo_rr_dd taken
from the iinn _ww_oo_rr_dd list. If iinn _ww_oo_rr_dd is omitted, then the ffoorr command exe-
cutes the ddoo _ll_ii_ss_tt once for each positional parameter that is set (see
``Parameter substitution'' below). Execution ends when there are no more
words in the list.
ccaassee _ww_oo_rr_dd iinn
[ _pp_aa_tt_tt_ee_rr_nn [ | _pp_aa_tt_tt_ee_rr_nn ] ... )) _ll_ii_ss_tt
;;;; ]
eessaacc
A ccaassee command executes the _ll_ii_ss_tt associated with the first _pp_aa_tt_tt_ee_rr_nn that
matches _ww_oo_rr_dd. The form of the patterns is the same as that used for
filename generation (see ``Filename generation'' below).
iiff _ll_ii_ss_tt
tthheenn
_ll_ii_ss_tt
[ eelliiff _ll_ii_ss_tt tthheenn
_ll_ii_ss_tt ]
...
[ eellssee _ll_ii_ss_tt ]
ffii
The _ll_ii_ss_tt following iiff is executed and, if it returns a zero exit status,
the _ll_ii_ss_tt following the first tthheenn is executed. Otherwise, the _ll_ii_ss_tt fol-
lowing eelliiff is executed and, if its value is zero, the _ll_ii_ss_tt following the
next tthheenn is executed. Failing that, the eellssee _ll_ii_ss_tt is executed. If no
eellssee _ll_ii_ss_tt or tthheenn _ll_ii_ss_tt is executed, then the iiff command returns a zero
exit status.
wwhhiillee _ll_ii_ss_tt
ddoo
_ll_ii_ss_tt
ddoonnee
A wwhhiillee command repeatedly executes the wwhhiillee _ll_ii_ss_tt and, if the exit
status of the last command in the list is zero, executes the ddoo _ll_ii_ss_tt;
otherwise the loop terminates. If no commands in the ddoo _ll_ii_ss_tt are exe-
cuted, then the wwhhiillee command returns a zero exit status; uunnttiill may be
used in place of wwhhiillee to negate the loop termination test.
uunnttiill _ll_ii_ss_tt
ddoo
_ll_ii_ss_tt
ddoonnee
uunnttiill is similar to wwhhiillee, only uunnttiill continues execution until the first
_ll_ii_ss_tt returns a zero exit status. In other words, uunnttiill works until the
test condition succeeds (it works the whole time the command is failing);
wwhhiillee works until the test condition fails. uunnttiill is useful when you are
waiting for a particular event to occur.
((_ll_ii_ss_tt))
Executes _ll_ii_ss_tt in a subshell.
{{_ll_ii_ss_tt;;}}
_ll_ii_ss_tt is simply executed.
_nn_aa_mm_ee (()) {{_ll_ii_ss_tt;;}}
Define a function which is referenced by _nn_aa_mm_ee. The body of functions is
the _ll_ii_ss_tt of commands between {{ and }}. Execution of functions is
described later (see ``Execution''.)
The following words are recognized only as the first word of a command
and when not quoted:
iiff tthheenn eellssee eelliiff ffii ccaassee eessaacc
ffoorr wwhhiillee uunnttiill ddoo ddoonnee {{ }}
_C_o_m_m_e_n_t_s
A word beginning with ## causes that word and all the following characters
up to a newline to be ignored.
_C_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n
The standard output from a command enclosed between grave accents ( `` `` )
may be used as part or all of a word; trailing newlines are removed.
No interpretation is done on the command string before the string is
read, except to remove backslashes (\\) used to escape other characters.
Backslashes may be used to escape grave accents (``) or other backslashes
and are removed before the command string is read. Escaping grave
accents allows nested command substitution. If the command substitution
lies within a pair of double quotes ( "" `` ...... `` "" ), backslashes used to
escape a double quote (\\"") will be removed; otherwise, they will be left
intact.
If a backslash is used to escape a newline character, both the backslash
and the newline are removed (see the section on ``Quoting''). In addi-
tion, backslashes used to escape dollar signs ( \\$$ ) are removed. Since
no interpretation is done on the command string before it is read,
inserting a backslash to escape a dollar sign has no effect. Backslashes
that precede characters other than \\, ``, "", nneewwlliinnee, and $$ are left
intact.
_P_a_r_a_m_e_t_e_r _s_u_b_s_t_i_t_u_t_i_o_n
The character $$ 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 parameter. Positional parameters may be
assigned values by sseett. Keyword parameters, (also known as variables)
may be assigned values by writing:
_nn_aa_mm_ee _== _vv_aa_ll_uu_ee [ _nn_aa_mm_ee _== _vv_aa_ll_uu_ee ] ...
Pattern-matching is not performed on _vv_aa_ll_uu_ee. There cannot be a function
and a variable with the same name.
$${{_pp_aa_rr_aa_mm_ee_tt_ee_rr}}
A _pp_aa_rr_aa_mm_ee_tt_ee_rr is a sequence of letters, digits, or underscores (a
_n_a_m_e), a digit, or any of the characters **, @@, ##, ??, --, $$, and !!.
The value, if any, of the parameter is substituted. The braces are
required only when _pp_aa_rr_aa_mm_ee_tt_ee_rr is followed by a letter, digit, or
underscore that is not to be interpreted as part of its name. A
_n_a_m_e must begin with a letter or underscore. If _pp_aa_rr_aa_mm_ee_tt_ee_rr is a
digit then it is a positional parameter. If _pp_aa_rr_aa_mm_ee_tt_ee_rr is ** or @@,
then all the positional parameters, starting with $$11, are substi-
tuted (separated by spaces). Parameter $$00 is set from argument zero
when the shell is invoked.
$${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::--_ww_oo_rr_dd}}
If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute its
value; otherwise substitute _ww_oo_rr_dd.
$${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::==_ww_oo_rr_dd}}
If _pp_aa_rr_aa_mm_ee_tt_ee_rr is not set or is null, then set it to _ww_oo_rr_dd; the value
of the parameter is then substituted. Positional parameters may not
be assigned to in this way.
$${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::??_ww_oo_rr_dd}}
If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute its
value; otherwise, print _ww_oo_rr_dd and exit from the shell. If _ww_oo_rr_dd is
omitted, the message ``parameter null or not set'' is printed.
$${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::++_ww_oo_rr_dd}}
If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute _ww_oo_rr_dd;
otherwise substitute nothing.
In the above, _ww_oo_rr_dd is not evaluated unless it is to be used as the sub-
stituted string, so that in the following example, ppwwdd is executed only
if dd is not set or is null:
eecchhoo $${{dd::--((ggaappwwdd``}}
If the colon (::) is omitted from the above expressions, then the shell
only checks whether _pp_aa_rr_aa_mm_ee_tt_ee_rr is set.
The following parameters are automatically set by the shell:
## The number of positional parameters in decimal
-- Flags supplied to the shell on invocation or by the sseett command
?? The decimal value returned by the last synchronously executed com-
mand
$$ The process number of this shell
!! The process number of the last background command invoked
The following parameters are used by the shell:
CCDDPPAATTHH Defines search path for the ccdd command. See the section
``cd'' under ``Special commands'' below.
HHOOMMEE The default argument (home directory) for the ccdd command
PPAATTHH The search path for commands (see ``Execution'' below)
MMAAIILL If this variable is set to the name of a mail file, then
the shell informs the user of the arrival of mail in the
specified file
MMAAIILLCCHHEECCKK This parameter specifies how often (in seconds) the shell
will check for the arrival of mail in the files specified
by the MMAAIILLPPAATTHH or MMAAIILL parameters. The default value is
600 seconds (10 minutes). If set to 0, the shell will
check before each prompt.
MMAAIILLPPAATTHH A colon ((::)) separated list of filenames. If this parameter
is set, the shell informs the user of the arrival of mail
in any of the specified files. Each filename can be fol-
lowed by ``%'' and a message that will be printed when the
modification time changes. The default message is
``you have mail''.
PPSS11 Primary prompt string, by default ``$$ ''
PPSS22 Secondary prompt string, by default ``>> ''
IIFFSS Internal field separators, normally ssppaaccee, ttaabb, and nneewwlliinnee
SSHHEELLLL When the shell is invoked, it scans the environment (see
``Environment'' 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.
The shell gives default values to PPAATTHH, PPSS11, PPSS22, and IIFFSS, while HHOOMMEE and
MMAAIILL are not set at all by the shell (although HHOOMMEE _i_s set by llooggiinn(M)).
_B_l_a_n_k _i_n_t_e_r_p_r_e_t_a_t_i_o_n
After parameter and command substitution, the results of substitution are
scanned for internal field separator characters (those found in IIFFSS) and
split into distinct arguments where such characters are found. Explicit
null arguments ( """" or '''' ) are retained. Implicit null arguments (those
resulting from _pp_aa_rr_aa_mm_ee_tt_ee_rr_ss that have no values) are removed.
_F_i_l_e_n_a_m_e _g_e_n_e_r_a_t_i_o_n
Following substitution, each command _ww_oo_rr_dd is scanned for the characters
**, ??, and [[. If one of these characters appears, the word is regarded as
a _pp_aa_tt_tt_ee_rr_nn. The word is replaced with alphabetically sorted filenames
that match the pattern. If no filename is found that matches the pat-
tern, the word is left unchanged. The character ``.'' at the start of a
filename or immediately following a ``/'', as well as the character ``/''
itself, must be matched explicitly. These characters and their matching
patterns are:
** 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
bracket ([[) is an exclamation mark (!!), then any character not
enclosed is matched.
_Q_u_o_t_i_n_g
The following characters have a special meaning to the shell and cause
termination of a word unless quoted:
; & ( ) | ^ < > newline space tab
A character may be _q_u_o_t_e_d (that is, made to stand for itself) by preced-
ing it with a ``\''. The pair \\nneewwlliinnee is ignored. All characters
enclosed between a pair of single quotation marks ('' ''), except a single
quotation mark, are quoted. Inside double quotation marks ("" ""), parame-
ter and command substitution occurs and ``\'' quotes the characters \\, ``,
"", and $$. ""$$**"" is equivalent to ""$$11 $$22 ..."", whereas ""$$@@"" is equivalent
to ""$$11"" ""$$22"" ...
_P_r_o_m_p_t_i_n_g
When used interactively, the shell prompts with the value of PPSS11 before
reading a command. If at any time a newline is typed and further input
is needed to complete a command, the secondary prompt (that is, the value
of PPSS22) is issued.
_S_p_e_l_l_i_n_g _c_h_e_c_k_e_r
When using ccdd(C) the shell checks spelling. For example, if you change
to a different directory using ccdd and misspell the directory name, the
shell responds with an alternative spelling of an existing directory.
Enter ``y'' and press <Return> (or just press <Return>) to change to the
offered directory. If the offered spelling is incorrect, enter ``n'',
then retype the command line. In this example the sshh(C) response is
boldfaced:
$ cd /usr/spol/uucp
ccdd //uussrr//ssppooooll//uuuuccpp??y
ookk
_I_n_p_u_t/_O_u_t_p_u_t
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 command.
They are _n_o_t passed on to the invoked command; substitution occurs before
_ww_oo_rr_dd or _dd_ii_gg_ii_tt is used:
<<_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard input (file descriptor 0).
>>_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard output (file descriptor 1). If
the file does not exist, it is created; otherwise, it is
truncated to zero length.
>>>>_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard output. If the file exists, out-
put is appended to it (by first seeking the end-of-file);
otherwise, the file is created.
<<<<[--]_ww_oo_rr_dd The shell input is read up to a line that is the same as
_ww_oo_rr_dd, or to an end-of-file. The resulting document becomes
the standard input. If any character of _ww_oo_rr_dd is quoted, no
interpretation is placed upon the characters of the docu-
ment; otherwise, parameter and command substitution occurs,
(unescaped) \\nneewwlliinnee is ignored, and ``\'' must be used to
quote the characters \\, $$, ``, and the first character of
_ww_oo_rr_dd. If ``-'' is appended to <<<<, all leading tabs are
stripped from _ww_oo_rr_dd and from the document.
<<&&_dd_ii_gg_ii_tt The standard input is duplicated from file descriptor _dd_ii_gg_ii_tt
(see dduupp(S)). Similarly for the standard output using >>.
<<&&-- The standard input is closed. Similarly for the standard
output using >>.
If one of the above is preceded by a digit, the file descriptor created
is that specified by the digit (instead of the default 0 or 1). For
example:
...... 22>>&&11
creates file descriptor 2 that is a duplicate of file descriptor 1.
If a command is followed by ``&'', the default standard input for the
command is the empty file /_d_e_v/_n_u_l_l. Otherwise, the environment for the
execution of a command contains the file descriptors of the invoking
shell as modified by input/output specifications.
_E_n_v_i_r_o_n_m_e_n_t
The _e_n_v_i_r_o_n_m_e_n_t (see eennvviirroonn(M)) 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. Executed commands inherit the
same environment. If the user modifies the values of these parameters or
creates new ones, none of these affect the environment unless the eexxppoorrtt
command is used to bind the shell's parameter to the environment. The
environment seen by any executed command is composed of any unmodified
name-value pairs originally inherited by the shell, minus any pairs
removed by uunnsseett, plus any modifications or additions, all of which must
be noted in eexxppoorrtt 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:
TTEERRMM==wwyy6600 _cc_mm_dd _aa_rr_gg_ss
and
(eexxppoorrtt TTEERRMM; TTEERRMM==wwyy6600; _cc_mm_dd _aa_rr_gg_ss)
are equivalent (as far as the above execution of _cc_mm_dd is concerned).
If the --kk flag is set, _a_l_l keyword arguments are placed in the environ-
ment, even if they occur after the command name.
_S_i_g_n_a_l_s
The IINNTTEERRRRUUPPTT and QQUUIITT 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. See the
ttrraapp command below.
_E_x_e_c_u_t_i_o_n
Each time a command is executed, the above substitutions are carried out.
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 executed in the shell process
(note how this differs from the execution of shell procedures). The posi-
tional parameters $$11,, $$22, ... 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 exe-
cute the command via eexxeecc(S).
The shell parameter PPAATTHH defines the search path for the directory con-
taining the command. Alternative directory names are separated by a
colon (::). The default path is :/_b_i_n:/_u_s_r/_b_i_n (specifying the current
directory, /_b_i_n, and /_u_s_r/_b_i_n, in that order). Note that the current
directory is specified by a null pathname, which can appear immediately
after the equal sign or between the colon delimiters anywhere else in the
path list. If the command name contains a ``/'', then the search path is
not used. Otherwise, each directory in the path is searched for an exe-
cutable file. If the file has execute permission but is not an _a._o_u_t
file, it is assumed to be a file containing shell commands. A subshell
(that is, a separate process) is spawned to read it. A parenthesized
command is also executed in a subshell.
Shell procedures are often used by users running the ccsshh. However, if
the first character of the procedure is a ``#'' (comment character), ccsshh
assumes the procedure is a ccsshh script, and invokes //bbiinn//ccsshh to execute
it. Always start sshh procedures with some other character if ccsshh users are
to run the procedure at any time. This invokes the standard shell
//bbiinn//sshh.
The location in the search path where a command was found is remembered
by the shell (to help avoid unnecessary eexxeeccs later). If the command was
found in a relative directory, its location must be re-determined when-
ever the current directory changes. The shell forgets all remembered
locations whenever the PPAATTHH variable is changed or the hhaasshh --rr command is
executed (see hhaasshh in next section).
_S_p_e_c_i_a_l _c_o_m_m_a_n_d_s
Input/output redirection is permitted for these commands:
:: No effect; the command does nothing. A zero exit code is returned.
.. _ff_ii_ll_ee
Reads and executes commands from _ff_ii_ll_ee and returns. The search path
specified by PPAATTHH is used to find the directory containing _ff_ii_ll_ee.
bbrreeaakk [ _nn ]
Exits from the enclosing ffoorr, wwhhiillee, or uunnttiill loop, if any. If _nn is
specified, it breaks _nn levels.
ccoonnttiinnuuee [ _nn ]
Resumes the next iteration of the enclosing ffoorr, wwhhiillee, or uunnttiill
loop. If _nn is specified, it resumes at the _nn-th enclosing loop.
ccdd [ _aa_rr_gg ]
Changes the current directory to _aa_rr_gg. The shell parameter HHOOMMEE is
the default _aa_rr_gg. The shell parameter CCDDPPAATTHH defines the search path
for the directory containing _aa_rr_gg. Alternative directory names are
separated by a colon (:). The default path is <null> (specifying
the current directory). Note that the current directory is speci-
fied by a null path name, which can appear immediately after the
equal sign or between the colon delimiters anywhere else in the path
list. If _aa_rr_gg begins with a ``/'', the search path is not used.
Otherwise, each directory in the path is searched for _aa_rr_gg.
If the shell is reading its commands from a terminal, and the speci-
fied directory does not exist (or some component cannot be
searched), spelling correction is applied to each component of
_d_i_r_e_c_t_o_r_y, in a search for the ``correct'' name. The shell then
asks whether or not to try and change directory to the corrected
directory name; an answer of nn means ``no'', and anything else is
taken as ``yes''.
eecchhoo [ _aa_rr_gg ]
Writes arguments separated by blanks and terminated by a newline on
the standard output. Arguments may be enclosed in quotes. Quotes
are required so that the shell correctly interprets these special
escape sequences:
\\bb Backspace
\\cc Prints line without newline.
\\ff Form feed
\\nn Newline
\\rr Carriage return
\\tt Tab
\\vv Vertical tab
\\\\ Backslash
\\_nn The 8-bit character whose ASCII code is the 1, 2 or 3-digit
octal number _nn. _nn must start with a zero.
eevvaall [ _aa_rr_gg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
eexxeecc [ _aa_rr_gg ... ]
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.
eexxiitt [ _nn ]
Causes the shell to exit with the exit status specified by _nn. If _nn
is omitted, the exit status is that of the last command executed.
An end-of-file will also cause the shell to exit.
eexxppoorrtt [ _nn_aa_mm_ee ... ]
The given _nn_aa_mm_ees 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.
ggeettooppttss
Used in shell scripts to support command syntax standards (see
IInnttrroo(C)); it parses positional parameters and checks for legal
options. See ggeettooppttss(C) for usage and description.
hhaasshh [ --rr ] [ _nn_aa_mm_ee ... ]
For each _nn_aa_mm_ee, the location in the search path of the command speci-
fied by _nn_aa_mm_ee is determined and remembered by the shell. The --rr
option causes the shell to forget all remembered locations. If no
arguments are given, information about remembered commands is
presented. ``Hits'' is the number of times a command has been
invoked by the shell process. ``Cost'' is a measure of the work
required to locate a command in the search path. There are certain
situations which require that the stored location of a command be
recalculated. Commands for which this will be done are indicated by
an asterisk (**) adjacent to the ``hits'' information. ``Cost'' will
be incremented when the recalculation is done.
nneewwggrrpp [ _aa_rr_gg ... ]
Equivalent to eexxeecc nneewwggrrpp _aa_rr_gg ...
ppwwdd Print the current working directory. See ppwwdd(C) for usage and
description.
rreeaadd [ _nn_aa_mm_ee ... ]
One line is read from the standard input and the first word is
assigned to the first _nn_aa_mm_ee, the second word to the second _nn_aa_mm_ee,
etc., with leftover words assigned to the last _nn_aa_mm_ee. The return
code is 0 unless an end-of-file is encountered.
rreeaaddoonnllyy [ _nn_aa_mm_ee ... ]
The given _nn_aa_mm_ees are marked rreeaaddoonnllyy and the values of these _nn_aa_mm_ees
may not be changed by subsequent assignment. If no arguments are
given, a list of all rreeaaddoonnllyy names is printed.
rreettuurrnn [ _nn ]
Causes a function to exit with the return value specified by _nn. If
_nn is omitted, the return status is that of the last command
executed.
sseett [ --aaeeffhhkknnuuvvxx [ _aa_rr_gg ... ] ]
--aa Mark variables which are modified or created for export.
--ee If the shell is noninteractive, exits immediately if a command
exits with a nonzero exit status.
--ff Disables filename generation.
--hh Locates and remembers function commands as functions are defined
(function commands are normally located when the function is
executed). For example, if hh is set, /_b_i_n/_t_t_y is added to the
hash table when:
showtty(){
tty
}
is declared. If hh is unset, the function is not added to the
hash table until showtty is called.
--kk Places all keyword arguments in the environment for a command,
not just those that precede the command name.
--nn Reads commands but does not execute them.
--uu Treats unset variables as an error when substituting.
--vv Prints shell input lines as they are read.
--xx Prints commands and their arguments as they are executed.
Although this flag is passed to subshells, it does not enable
tracing in those subshells.
---- Does 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 $$11, $$22, ... If no arguments are given, the values of all
names are printed.
sshhiifftt [_nn]
The positional parameters from $$22 ... are renamed $$11 ... If _nn is
specified, shift the positional parameters by _nn places. sshhiifftt is the
only way to access positional parameters above $$99.
tteesstt Evaluates conditional expressions. See tteesstt(C) for usage and
description.
ttiimmeess
Prints the accumulated user and system times for processes run from
the shell.
ttrraapp [ _aa_rr_gg ] [ _nn ] ...
_aa_rr_gg is a command to be read and executed when the shell receives
signal(s) _nn. (Note that _aa_rr_gg is scanned once when the trap is set
and once when the trap is taken.) Trap commands are executed in
order of signal number. The highest signal number allowed is 16.
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 _aa_rr_gg is absent, all trap(s) _nn
are reset to their original values. If _aa_rr_gg is the null string, this
signal is ignored by the shell and by the commands it invokes. If _nn
is 0, the command _aa_rr_gg is executed on exit from the shell. The ttrraapp
command with no arguments prints a list of commands associated with
each signal number.
ttyyppee [ _nn_aa_mm_ee ... ]
For each _nn_aa_mm_ee, indicate how it would be interpreted if used as a
command name.
uulliimmiitt [ _nn ]
imposes a size limit of _nn blocks on files written by the shell and
its child processes (files of any size may be read). Any user may
decrease the file size limit, but only the super user (_r_o_o_t) can
increase the limit. With no argument, the current limit is printed.
If no option is given and a number is specified, --ff is assumed.
uunnsseett [ _nn_aa_mm_ee ... ]
For each _nn_aa_mm_ee, remove the corresponding variable or function. The
variables PPAATTHH, PPSS11, PPSS22, MMAAIILLCCHHEECCKK and IIFFSS cannot be unset.
uummaasskk [ _oo_oo_oo ]
The user file-creation mask is set to the octal number _oo_oo_oo where _oo
is an octal digit (see uummaasskk(C)). If _oo_oo_oo is omitted, the current
value of the mask is printed.
wwaaiitt [ _nn ]
Waits for the specified process to terminate, and reports the termi-
nation status. If _nn is not given, all currently active child pro-
cesses are waited for. The return code from this command is always
0.
_I_n_v_o_c_a_t_i_o_n
If the shell is invoked through eexxeecc(S) and the first character of argu-
ment 0 is ``-'', commands are initially read from /_e_t_c/_p_r_o_f_i_l_e and then
from $$HHOOMMEE/._p_r_o_f_i_l_e, if such files exist. Thereafter, commands are read
as described below, which is also the case when the shell is invoked as
//bbiinn//sshh. The flags below are interpreted by the shell on invocation
only; note that unless the --cc or --ss flag is specified, the first argument
is assumed to be the name of a file containing commands, and the remain-
ing arguments are passed as positional parameters to that command file:
--cc _ss_tt_rr_ii_nn_gg If the --cc flag is present, commands are read from _ss_tt_rr_ii_nn_gg.
--ss If the --ss flag is present or if no arguments remain, commands
are read from the standard input. Any remaining arguments
specify the positional parameters. Shell output is written to
file descriptor 2.
--tt If the --tt flag is present, a single command is read and exe-
cuted, and the shell exits. This flag is intended for use by C
programs only and is not useful interactively.
--ii If the --ii 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, TTEERRMMIINNAATTEE is ignored (so that kkiillll 00 does not kill an
interactive shell) and IINNTTEERRRRUUPPTT is caught and ignored (so that
wwaaiitt is interruptible). In all cases, QQUUIITT is ignored by the
shell.
--rr If the --rr flag is present, the shell is a restricted shell (see
rrsshh(C)).
The remaining flags and arguments are described under the sseett command
above.
_E_x_i_t _s_t_a_t_u_s
Errors detected by the shell, such as syntax errors, cause the shell to
return a nonzero exit status. If the shell is being used noninterac-
tively, execution of the shell file is abandoned. Otherwise, the shell
returns the exit status of the last command executed. See the eexxiitt com-
mand above.
_F_i_l_e_s
/_e_t_c/_p_r_o_f_i_l_e system default _p_r_o_f_i_l_e, read by login shells before
$$HHOOMMEE/._p_r_o_f_i_l_e
$$HHOOMMEE/._p_r_o_f_i_l_e read by login shell at login
/_t_m_p/_s_h* temporary file for <<<<
/_d_e_v/_n_u_l_l source of empty file
_S_e_e _a_l_s_o
aa..oouutt(FP), ccdd(C), dduupp(S), eennvv(C), eennvviirroonn(M), eexxeecc(S), ffoorrkk(S), kksshh(C),
llooggiinn(M), nneewwggrrpp(C), ppiippee(S), pprrooffiillee(M), rrsshh(C), ssiiggnnaall(S), tteesstt(C),
uummaasskk(C), uummaasskk(S) and wwaaiitt(S).
_N_o_t_e_s
The command rreeaaddoonnllyy (without arguments) produces the same type of output
as the command eexxppoorrtt.
If <<<< is used to provide standard input to an asynchronous process
invoked by &&, the shell gets mixed up about naming the input document; a
garbage file /_t_m_p/_s_h* is created and the shell complains about not being
able to find that file by another name.
If a command is executed, and a command with the same name is installed
in a directory in the search path before the directory where the original
command was found, the shell will continue to eexxeecc the original command.
Use the hhaasshh command to correct this situation.
If you move the current directory or one above it, ppwwdd may not give the
correct response. Use the ccdd command with a full pathname to correct
this situation.
When a sshh user logs in, the system reads and executes commands in
/_e_t_c/_p_r_o_f_i_l_e before executing commands in the user's $$HHOOMMEE/._p_r_o_f_i_l_e. You
can, therefore, modify the environment for all sshh users on the system by
editing /_e_t_c/_p_r_o_f_i_l_e.
The shell doesn't treat the high (eighth) bit in the characters of a com-
mand line argument specially, nor does it strip the eighth bit from the
characters of error messages. Previous versions of the shell used the
eighth bit as a quoting mechanism.
Existing programs that set the eighth bit of characters in order to quote
them as part of the shell command line should be changed to use of the
standard shell quoting mechanisms (see the section on ``Quoting'').
Words used to specify filenames in input/output redirection are not
expanded for filename generation (see the section on ``Filename
generation''). For example, ccaatt ffiillee11 >> aa** will create a file named _a*.
Because commands in pipelines are run as separate processes, variables
set in a pipeline have no effect on the parent shell.
If you get the error message:
fork failed - too many processes
try using the wwaaiitt(C) command to clean up your background processes. If
this doesn't help, the system process table is probably full or you have
too many active foreground processes (there is a limit to the number of
processes that be can associated with your login, and the number the sys-
tem can keep track of).
_W_a_r_n_i_n_g_s
Not all processes of a 3 or more stage pipeline are children of the
shell, and thus cannot be waited for.
For wwaaiitt _nn, if _nn is not an active process id, all your shell's currently
active background processes are waited for and the return code will be
zero.
_S_t_a_n_d_a_r_d_s _c_o_n_f_o_r_m_a_n_c_e
sshh is conformant with:
AT&T SVID Issue 2;
and X/Open Portability Guide, Issue 3, 1989.