sh(C)
sh --
invoke the shell command interpreter
Syntax
sh [ -aceikLnrstuvx ] [ args ]
Description
The shell is the standard command programming language that executes
commands read from a terminal or a file. The shell reads lines and
either executes them (if they are an external program), or
interprets them as statements in the shell programming language.
Each input line is scanned and split into tokens; parameters are
substituted (subject to quoting), filenames are generated, input and
output are (optionally) redirected, then the commands are executed.
See ``Invocation'' for the meaning of arguments to the shell.
NOTE: If you require the functionality supplied
by sh as defined by ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992) and X/Open CAE Specification, Commands and Utilities, Issue 4, 1992, refer to
ksh(C),
which documents /bin/posix/sh.
Commands
A simple-command is a sequence of non-blank
words separated by blanks (a blank 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
exec(S)).
The value of a simple-command is its exit status if it
terminates normally. If it terminates abnormally, it returns the
value of the exit signal number + SIGFLG, where
SIGFLG is (octal) 0200. See
signal(S)
for a list of signal numbers.
A pipeline is a sequence of one or more commands
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 command but the last is connected by a
pipe(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 list 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 symbols && 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 not wait for that
pipeline to finish). The symbol && causes the list
following it to be executed if the preceding pipeline succeeded
(returned a 0 exit status). The symbol || causes the list
following it to be executed only if the preceding pipeline failed
(returned a non-zero exit status). An arbitrary number of newlines
may appear in a list, instead of semicolons, to delimit
commands.
A command 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:
for name [ in word ... ]
do
list
done
Each time a for command is executed, name is set
to the next word taken from the in
word list. If in word is omitted, then
the for command executes the do list
once for each positional parameter that is set (see ``Parameter
substitution''). Execution ends when there are no more words in the
list.
case word in
[ pattern [ | pattern ] ... ) list
;; ]
esac
A case command executes the list associated with
the first pattern that matches word. The form of
the patterns is the same as that used for filename generation (see
regexp(M)
for details).
if list
then
list
[ elif list
then
list ]
...
[ else list ]
fi
The list following if is executed and, if it
returns a 0 exit status, the list following the first
then is executed. Otherwise, the list following
elif is executed and, if its value is 0, the
list following the next then is
executed. Failing that, the else list is
executed. If no else list or then
list is executed, then the if command returns a
0 exit status. Note that the then keyword must fall on a
new line.
while list
do
list
done
A while command repeatedly executes the while
list and, if the exit status of the last command in the
list is 0, executes the do list; otherwise the
loop terminates. If no commands in the do list
are executed, then the while command returns a 0 exit
status; until may be used in place of while to
negate the loop termination test.
until list
do
list
done
until is similar to while, except that
until continues execution until the first list
returns a 0 exit status. In other words, until works until
the test condition succeeds (it works the whole time the command is
failing); while works until the test condition
fails. until is useful when you are waiting for a
particular event to occur.
(list)
This executes list in a subshell.
{list;}
This simply executes list.
name ( ) {list;}
This defines a function which is referenced by name. The
body of functions is the list of commands between
{ and }. Execution of functions is described
later (see ``Execution'').
The following words are reserved only when they are the first word
of a command and when they are not quoted:
if then else elif fi case esac
for while until do done { }
Comments
A word beginning with # causes that word and all the
following characters up to a newline to be ignored.
Command substitution
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 (\") are removed; otherwise, they
are 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 addition, 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
\, `, ", newline, and $ are left intact.
Parameter substitution
The character $ is used to introduce substitutable
parameters. There are two types of parameters, positional
and keyword. If a parameter is a digit, it is a positional
parameter. Positional parameters may be assigned values by
set. Keyword parameters, (also known as variables) may be
assigned values by writing:
name = value [ name = value ] ...
Pattern-matching is not performed on value. There cannot
be a function and a variable with the same name.
${parameter}-
A parameter is a sequence of letters, digits, or
underscores (a name), a digit, or any of the characters
, @, #, ?, -, $, and !. The value, if any, of the parameter is
substituted. The braces are required only when parameter
is followed by a letter, digit, or underscore that is not to be
interpreted as part of its name. A name must begin with a
letter or underscore. If parameter is a digit then it is a
positional parameter. If parameter is or
@, then all the positional parameters, starting with
$1, are substituted (separated by spaces). Parameter
$0 is set from argument 0 when the shell is invoked.
${parameter:-word}-
If parameter is set and is not a null argument, its value
is substituted; otherwise word is substituted.
${parameter:=word}-
If parameter is not set or is null, then it is set to
word; the value of the parameter is then
substituted. Positional parameters may not be assigned to in this
way.
${parameter:?word}-
If parameter is set and is not a null argument, its value
is substituted; otherwise, word is printed and the shell
is exited. If word is omitted, the message ``parameter
null or not set'' is printed.
${parameter:+word}-
If parameter is set and is not a null argument,
word is substituted; otherwise nothing is substituted.
In the above, word is not evaluated unless it is to be
used as the substituted string, so that in the following example,
pwd is executed only if d is not set or is null:
echo ${d:- `pwd` }
If the colon (:) is omitted from the above expressions,
then the shell only checks whether parameter 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 set
command
?-
The decimal value returned by the last synchronously executed
command
$-
The process number of this shell
!-
The process number of the last background command invoked
The following parameters are used by the shell:
CDPATH-
The search path for the cd special command. See the
section for cd under ``Special commands''.
HOME-
The default argument (home directory) for the cd special
command.
IFS-
Internal field separators, normally space, tab, and newline.
MAIL-
If this variable is set to the name of a mail file, then the shell
informs the user of the arrival of mail in the specified file.
MAILCHECK-
This parameter specifies how often (in seconds) the shell checks for
the arrival of mail in the files specified by the MAILPATH
or MAIL parameters. The default value is 600 seconds (10
minutes). If it is set to 0, the shell checks before each prompt.
MAILPATH-
A colon (:) separated list of filenames. If this parameter
is set, the shell informs the user of the arrival of mail in any of
the specified files. Each filename can be followed by ``%''
and a message to be printed when the modification time changes. The
default message is ``you have mail''.
PATH-
The search path for commands (see ``Execution'').
PS1-
The primary prompt string, by default ``$ ''.
PS2-
The secondary prompt string, by default ``> ''.
SHELL-
When the shell is invoked, it scans the environment (see
``Environment'') for this name. If it is found and there is an `r'
in the filename part of its value, the shell becomes a restricted
shell.
The shell gives default values to PATH, PS1,
PS2, and IFS, while HOME and
MAIL are not set at all by the shell (although
HOME is set by
login(M)).
Blank interpretation
After parameter and command substitution, the results of
substitution are scanned for internal field separator characters
(those found in IFS) and split into distinct arguments
where such characters are found. Explicit null arguments
("" or '') are retained. Implicit null
arguments (those resulting from parameters that have no
values) are removed.
Filename generation
Following substitution, each command word is scanned for patterns
(shell regular expressions), as described in
regexp(M).
Quoting
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 quoted (that is, made to stand for
itself) by preceding it with a ``\''. The pair \newline is
ignored. All characters enclosed between a pair of single quotation
marks (' '), except a single quotation mark, are quoted. Inside
double quotation 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 newline is
typed and further input is needed to complete a command, the
secondary prompt (that is, the value of PS2) is issued.
Spelling checker
When using
cd(C)
the shell checks spelling. For example, if you change to a different
directory using cd 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 user input is
boldfaced:
$ cd /usr/spool/uucp
cd /usr/spool/uucp?
y
ok
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
command. They are not passed on to the invoked command;
substitution occurs before word or digit is
used:
<word-
Use file word as standard input (file descriptor 0).
>word-
Use file word 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 word as standard output. If the file exists,
output is appended to it (by first seeking the end-of-file);
otherwise, the file is created.
<<[ - ]word-
Read the shell input up to a line that is the same as
word, or to an end-of-file. The resulting document
becomes the standard input. If any character of word is
quoted, no interpretation is placed upon the characters of the
document; otherwise, parameter and command substitution occurs,
(unescaped) \newline is ignored, and ``\'' must be used to
quote the characters \, $, `, and the first character of
word. If ``-'' is appended to <<, all
leading tabs are stripped from word and from the document.
<&digit-
Duplicate the standard input from file descriptor digit
(see
dup(S));
similarly for the standard output using >.
<&--
Close the standard input; 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:
... 2>&1
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 /dev/null. Otherwise,
the environment for the execution of a command contains the file
descriptors of the invoking shell as modified by input/output
specifications.
Environment
The environment (see
environ(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
export 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 unset, plus any
modifications or additions, all of which must be noted in
export commands.
The environment for any simple-command may be augmented
by prefixing it with one or more assignments to parameters.
Thus the following two statements are equivalent (as far as the
above execution of cmd is concerned).
TERM=wy60 cmd args
(export TERM; TERM=wy60; cmd args)
If the -k flag is set, all keyword arguments
are placed in the environment, even if they occur after the command
name.
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. See the trap
command.
Execution
Each time a command is executed, the substitutions described in the
previous sections are carried out. If the command name does not
match a special command, 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 positional
parameters $1, $2, ... are set to the arguments of the
function. If the command name matches neither a special
command nor the name of a defined function, a new process is
created and an attempt is made to execute the command via
exec(S).
The shell parameter PATH defines the search path for the
directory containing the command. Alternative directory names are
separated by a colon (:). The default path is
:/bin:/usr/bin (specifying the current directory,
/bin, and /usr/bin, 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 executable file. If
the file has execute permission but is not an a.out 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 sub-shell.
Shell procedures are often used by users running the csh.
However, if the first character of the procedure is a ``#''
(comment character), csh assumes the procedure is a
csh script, and invokes /bin/csh to execute
it. sh procedures should always be started with some other
character if csh users are to run the procedure at any
time. This invokes the standard shell /bin/sh.
The location in the search path where a command was found is
remembered by the shell (to help avoid unnecessary execs
later). If the command was found in a relative directory, its
location must be re-determined whenever the current directory
changes. The shell forgets all remembered locations whenever the
PATH variable is changed or the hash -r command
is executed (see hash in the next section).
Special commands
Input/output redirection is permitted for these commands:
:-
No effect; the command does nothing. A 0 exit code is returned.
. file-
Reads and executes commands from file and returns. The
search path specified by PATH is used to find the
directory containing file.
break [ n ]-
Exits from the enclosing for, while, or
until loop, if any. If n is specified, it breaks
n levels.
continue [ n ]-
Resumes the next iteration of the enclosing for,
while, or until loop. If n is
specified, it resumes at the nth enclosing loop.
cd [ -L | -P ] [ arg ]-
Changes the current directory to arg. The shell parameter
HOME is the default arg. The shell parameter
CDPATH defines the search path for the directory
containing arg. Alternative directory names are separated
by a colon (:). The default path is <null> (specifying the current
directory). 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
arg begins with a ``/'', the search path is not
used. Otherwise, each directory in the path is searched for
arg.
If the shell is reading its commands from a terminal, and the
specified directory does not exist (or some component cannot be
searched), spelling correction is applied to each component of
arg, 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 n means ``no'', and anything
else is taken as ``yes''.
The -L and -P flags are relevant to systems
with symbolic links:
-L-
Preserve logical pathnames so that cd -L .. moves up
one component towards the root along the current logical path.
-P-
Use a physical model for pathnames so that cd -L ..
moves up one component towards the root by following the link to the
parent of the current directory. This is the default behavior.
For example, if /usr/include/sys/h is a symbolic link to
the directory /sys/h, then
cd /usr/include/sys/h; cd -L .. would make
/usr/include/sys the current directory; cd
/usr/include/sys/h; cd -P .. would make /sys the
current directory.
If the -L option is specified to sh (or to
set), the default behavior of cd is to use
logical pathnames.
echo [ arg ]-
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:
\b Backspace
\c Prints line without newline
\f Form feed
\n Newline
\r Carriage return
\t Tab
\v Vertical tab
\\ Backslash
\n The 8-bit character whose ASCII code is the 1, 2 or 3-digit
octal number n. n must start with a 0
eval [ arg ... ]-
Reads the arguments as input to the shell and executes the resulting
command(s).
exec [ arg ... ]-
Executes the command specified by the arguments 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 the 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 also causes the shell to
exit.
export [ name ... ]-
Marks the given names for automatic export to the
environment of subsequently executed commands. If no
arguments are given, a list of all names that are exported in this
shell is printed.
getopts-
Is used in shell scripts to support command syntax standards (see
Intro(C));
it parses positional parameters and checks for legal options. See
getopts(C)
for usage and description.
hash [ -r ] [ name ... ]-
Determines and remembers, for each name, the location in
the search path of the command specified by name. The
-r 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 is
done are indicated by an asterisk () adjacent to the
``hits'' information. ``Cost'' is incremented when the
recalculation is done.
newgrp [ arg ... ]-
Equivalent to exec newgrp arg ...
pwd [ -L | -P ]-
Prints the current working directory. The -L and
-P flags are useful with symbolic links:
-L-
Show the logical pathname to the directory preserving the route
taken to get there.
-P-
Show the physical pathname to the directory. This is the default
behavior.
For example, if /usr/include/sys/h is a symbolic link to
the directory /sys/h, then
cd /usr/include/sys/h; pwd -L prints
/usr/include/sys/h as the current working directory;
cd/usr/include/sys/h; pwd -P prints
/sys/h as the current working directory.
If the -L option is specified to sh (or to
set), the default behavior of pwd is to use
logical pathnames.
read [ name ... ]-
Reads one line from the standard input and assigns the first word to
the first name, the second word to the second
name, and so on, with leftover words assigned to the last
name. The return code is 0 unless an end-of-file is
encountered.
readonly [ name ... ]-
Marks the given names read-only; the values of these
names may not be changed by subsequent assignment.
If no arguments are given, a list of all read-only
names is printed.
return [ n ]-
Causes a function to exit with the return value specified by
n. If n is omitted, the return status is that of
the last command executed.
set [ -aefhknuvx [ arg ... ] ]-
set takes the following options:
-a-
Marks variables which are modified or created for export.
-e-
If the shell is non-interactive, exits immediately if a command
exits with a non-zero exit status.
-f-
Disables filename generation.
-h-
Locates and remembers function commands as functions are defined
(function commands are normally located when the function is
executed). For example, if h is set, /bin/tty is
added to the hash table when:
showtty(){
tty
}
is declared. If h is unset, the function is not added to
the hash table until showtty is called.
-k-
Places all keyword arguments in the environment for a command,
not just those that precede the command name.
-L-
Causes the internal cd and pwd commands to use
logical pathnames by default rather than physical pathnames.
-n-
Reads commands but does not execute them.
-u-
Treats unset variables as an error when substituting.
-v-
Prints shell input lines as they are read.
-x-
Prints commands and their arguments as they are executed. Although
this flag is passed to sub-shells, it does not enable tracing in
those sub-shells.
---
Does not change any of the flags; this is 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]-
Renames the positional parameters from $2 ... to
$1 ... If n is specified, it shifts the
positional parameters by n places. shift is the
only way to access positional parameters above $9.
test-
Evaluates conditional expressions. See
test(C)
for usage and description.
times-
Prints the accumulated user and system times for processes run from
the shell.
trap [ arg ] [ n ] ...-
arg is a command to be read and executed when the shell
receives signal(s) n. (Note that arg 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 arg
is absent, all trap(s) n are reset to their original
values. If arg is the null string, this signal is ignored
by the shell and by the commands it invokes. If n is 0,
the command arg is executed on exit from the shell. The
trap command with no arguments prints a list of commands
associated with each signal number.
type [ name ... ]-
Indicates, for each name, how it would be interpreted if
used as a command name.
ulimit [ n ]-
Imposes a size limit of n 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 root can
increase the limit. With no argument, the current limit is
printed. If no option is given and a number is specified,
-f is assumed.
unset [ name ... ]-
Removes, for each name, the corresponding variable or
function. The variables PATH, PS1,
PS2, MAILCHECK and IFS cannot be
unset.
umask [ -S ] [ mask ]-
Sets the user file-creation mask to the value of the mask
operand. If mask is an octal integer, the specified bits
are set in the umask. Otherwise, mask should be
symbolic mode (see
chmod(C)),
the new value of the file-creation mask being the logical complement
of the file permission bits specified. If no mask is specified, the
current file-creation mask is printed. If -S is specified,
the symbolic form is printed. See also
umask(C).
wait [ n ]-
Waits for the specified process to terminate, and reports the
termination status. If n is not given, all currently
active child processes are waited for. The return code from this
command is always 0.
Invocation
If the shell is invoked through
exec(S)
and the first character of argument 0 is ``-'', commands are
initially read from /etc/profile and then from
$HOME/.profile, 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 containing 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
string.
-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 is written to file
descriptor 2.
-t-
If the -t flag is present, a single command is read and
executed, and the shell exits. This flag is intended for use by C
programs only and is not useful interactively.
-i-
If the -i flag is present or if the shell input and
output are attached to a terminal, this shell is
interactive. In this case, TERMINATE is ignored
(so that kill 0 does not kill an interactive shell) and
INTERRUPT is caught and ignored (so that wait is
interruptible). In all cases, QUIT is ignored by the
shell.
-r-
If the -r flag is present, the shell is a restricted
shell (see
rsh(C)).
The remaining flags and arguments are described under the
set command in ``Special commands''.
Exit values
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 the exit command above.
Examples
See
``Solving problems with the environment''
and
Chapter 11, ``Automating frequent tasks''
in the Operating System User's Guide
in the SCO OpenServer Operating System User's Guide
for a general introduction to shell programming, and the development
of an example script.
See
See ``Tuning script performance''
in the Operating System User's Guide
for a general discussion of shell script efficiency considerations
and some examples of generic scripts.
Notes
The command readonly (without arguments) produces the same
type of output as the command export.
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 /tmp/sh 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 continues to
exec the original command. Use the hash command
to correct this situation.
If you move the current directory or one above it, pwd may
not give the correct response. Use the cd command with a
full pathname to correct this situation.
When a sh user logs in, the system reads and executes
commands in /etc/profile before executing commands in the
user's $HOME/.profile. You can, therefore,
modify the environment for all sh users on the system by
editing /etc/profile.
The shell doesn't treat the high (eighth) bit in the characters of a
command 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, cat file1 > a creates 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
wait(C)
command to clean up your background processes. If this does not
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 can be associated with your login, and the number the
system can keep track of).
Warning
Not all processes of a 3 or more stage pipeline are children of the
shell, and thus cannot be waited for.
For wait n, if n is not an active
process ID, all your shell's currently active background
processes are waited for and the return code is 0.
Files
/etc/profile-
system default profile, read by login shells
$HOME/.profile-
read by login shell at login
/tmp/sh-
temporary file for <<
/dev/null-
source of empty file
Open UNIX 8 compatibility notes
When running ACP on Open UNIX 8 and UnixWare 7 systems,
set OSRCMDS=on to use
the SCO OpenServer version of the <sh> command.
This provides the expected behaviors
for SCO OpenServer applications.
The SCO OpenServer version of this command
is also provided on Open UNIX 8 systems under the OSP feature
See the
Running SCO OpenServer Applications
topic in the Open UNIX 8 documentation set.
See also
a.out(FP),
cd(C),
dup(S),
env(C),
environ(M),
exec(S),
fork(S),
ksh(C),
login(M),
newgrp(C),
pipe(S),
profile(M),
regexp(M),
rsh(C),
signal(S),
test(C),
umask(C),
umask(S),
wait(S)
Chapter 10, ``Configuring and working with the shells''
in the SCO OpenServer Operating System User's Guide
Standards conformance
sh is conformant with:
ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003