sh(1)
sh, jsh, rsh --
shell, the standard, job control, and restricted command interpreter
Synopsis
/usr/bin/sh [-acefhiknprstuvx] [args]
/u95/bin/sh [-abcefhikmnoprstuvxCD] [file] [-o option] ... [-] [args]
/usr/bin/jsh [-acefhiknprstuvx] [args]
/usr/lib/rsh [-acefhiknprstuvx] [args]
/sbin/sh [-acefhiknprstuvx] [args]
Description
The sh command interpreter is a command programming language
that executes commands read from a terminal or a file.
The version of sh residing in /usr/bin/sh
is the Bourne shell and is described in this manual page.
The version residing in /u95/bin/sh
is a version of the Korn Shell that complies with
X/Open Interface Definitions, Version 4 Issue 2.
/u95/bin/sh is considered the standard shell when you want an
X/Open-compliant execution environment; see the
ksh(1)
manual
page for a description of /u95/bin/sh.
(Also see
profile(4)
for a description of how a shell is selected
for execution when you log in to the system.)
jsh is an interface to the shell which provides
all the functionality of sh and enables job control
(see ``Job control'', below).
/usr/lib/rsh
is a restricted version of the standard command interpreter
sh;
it is used to restrict logins to execution environments whose
capabilities are more controlled than those of the standard
shell.
See ``Invocation''
for the meaning of arguments to the shell.
sh, jsh, and rsh process supplementary code set
characters in command arguments, as values of variables
and field separators, in prompt strings, comments, and pipes,
and in scripts
according to the locale specified in the LC_CTYPE
environment variable (see LANG on
environ(5)).
Pattern searches are performed
on characters, not bytes, as described in Filename
Generation below.
Definitions
A
blank
is a tab or a space.
A
name
is a sequence of letters, digits, or underscores,
beginning with a letter or an underscore.
A
parameter
is a name, a digit, or any of the following characters:
*,
@,
#,
?,
-,
$,
and
!.
Commands
A
``simple-command''
is a sequence of non-blank
words separated by blanks.
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(2)).
The
value
of a simple-command is its exit status
if it terminates normally, or (octal) 200+status if
it terminates abnormally; see
signal(5)
for a list of
status values.
A
``pipeline''
is a sequence of one or more
commands separated by
|. (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(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 pipeline is the exit status of the
last command in the pipeline.
A
``list''
is a sequence of one or more
pipelines separated by
;,
&,
&&,
or
||,
and sometimes 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
(that is, the shell waits for the pipeline
to finish before executing any commands following
the semicolon); 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 only if the preceding
pipeline returns a
zero (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.
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'',
below).
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
file-name generation (see
``Filename generation'')
except that a slash, a leading dot, or a dot immediately
following a slash need not be matched explicitly.
if list then list [ elif list then list] ... [ else list] fi-
The
list
following if is executed and,
if it
returns a zero exit status, the
list
following
the first
then
is executed.
Otherwise, the
list
following elif
is executed and, if its value is zero,
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 zero exit status.
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 zero,
executes
the
do
list;
otherwise the loop terminates.
If no commands in the
do
list
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.
(list)-
Execute
list
in a sub-shell.
{ list;}-
list
is executed in the current (that is, parent) shell.
The { must be followed by a space.
name () { list;}-
Define a function
which is referenced by
name.
The body of the function
is the
list
of commands between
{ and }.
The list may appear on the same line as the {.
If it does, the { and list
must be separated by a space.
The } may not be on the same line as list;
it must be on a newline.
Execution of functions is described below
(see ``Execution'').
The { and } are unnecessary
if the body of the function is a simple-command
as defined above, under Commands.
The following words
are only recognized as the first word of a command and when not
quoted:
if then else elif fi case esac for while until do done { }
Comments
A word beginning with a
#
causes that word and all the following characters up to a
newline
to be ignored.
NOTE:
The exception to this is when #! shell is used as the first line
of a shell script.
See ``Execution''.
Command substitution
The shell interprets commands from the string between two backquotes
(``)
and the standard output from these commands may
be used as all or part of a word.
Trailing newlines from the
standard output are removed.
No interpretation is done on the string before the string is
read,
except to remove backslashes (\)
used to escape other characters.
Backslashes
may be used to escape a backquote
(`)
or another backslash (\) and are
removed before the command string is read.
Escaping backquotes allows nested command substitution.
If the command substitution lies within a pair of double
quotes
(" . . . ` . . . ` . . . "),
a backslash used to escape a double quote
(\")
will be removed; otherwise, it will be left intact.
If a backslash is used to escape a newline character
(\newline),
both the backslash and the newline are removed
(see ``Quoting'').
In addition, backslashes used to escape dollar signs
(\$) are removed.
Since no parameter substitution 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 when the command string is read.
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}-
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.
If
parameter
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.
${parameter:-word}-
If
parameter
is set and is non-null, substitute its value;
otherwise substitute
word.
${parameter:=word}-
If
parameter
is not set or is null
set it to
word;
the value of the parameter is substituted.
Positional parameters may not be assigned
in this way.
${parameter:?word}-
If
parameter
is set and is non-null, substitute its value;
otherwise, print
parameter: word
and exit from the shell.
If
word
is omitted, the message
parameter null or not set
is printed.
${parameter:+word}-
If
parameter
is set and is non-null, substitute
word;
otherwise substitute nothing.
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, the
shell only checks whether
parameter
is set or not.
The following parameters are automatically set by the shell.
*-
Expands to the positional parameters, beginning with 1.
@-
Expands to the positional parameters, beginning with 1,
except when expanded within double quotes,
in which case each positional parameter
expands as a separate field.
#-
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.
$ reports the process ID of the parent shell
in all shell constructs, including pipelines,
and in parenthesized sub-shells.
!-
The process number of the last background command invoked.
The following parameters are used by the shell.
The parameters in this section are also referred to as
environment variables.
HOME-
The default argument (home directory) for the
cd
command, set to the user's login directory
by
login(1)
from the password file
(see
passwd(4)).
PATH-
The search path for commands (see
``Execution'',
below).
The user may not change
PATH
if executing under
/usr/lib/rsh.
CDPATH-
The search path for the
cd
command.
MAIL-
If this parameter is set to the name of a mail file
and
the
MAILPATH
parameter is not set, the shell informs the user of the arrival
of mail
in the specified 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.
The default value is 600 seconds (10 minutes).
If set to 0, the shell will check 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 that will be
printed when the
modification time changes.
The default message is
you have mail
.
PS1-
Primary prompt string, by default
$ .
PS2-
Secondary prompt string, by default
> .
IFS-
Internal field separators,
by default space, tab, and newline
(see ``Blank interpretation'').
LANG-
If this parameter is set, the shell will use it to determine the
current
locale; see
environ(5),
setlocale(3C).
SHACCT-
If this parameter is set to the name of a file writable by the
user,
the shell will write an accounting record in the file for each
shell
procedure executed.
SHELL-
When the shell is invoked, it scans the environment (see
``Environment'',
below) for this name.
If it is found and rsh is the filename part of its value,
the
shell becomes a restricted shell.
TIMEOUT-
A non-zero value for TIMEOUT
causes the shell to exit
after $TIMEOUT seconds of inactivity.
The default value is site dependent.
The original whitespace characters
(space, tab, and newline)
are always considered internal field separators.
NOTE:
This variable can only be set on a system-wide basis
in /etc/default/sh, and cannot be set in an
individual user's .profile.
The shell gives default values to
PATH, PS1, PS2, MAILCHECK, and IFS.
HOME
and
MAIL
are set by
login(1).
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.
Input/Output
A command's 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
and are
not
passed on as arguments to the invoked command.
Note that parameter and 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 to the end-of-file);
otherwise, the file is created.
<<[-]word-
After parameter and command substitution is done on
word,
the shell input is read up to the first line that
literally matches the resulting
word,
or to an end-of-file.
If, however,
-
is appended to
<<:
-
leading tabs are stripped from
word
before the shell input is read
(but after parameter and command substitution is done on
word),
-
leading tabs are stripped from
the shell input as it is read and before each line is compared
with
word,
and
-
shell input is read up to the first line that literally matches
the resulting
word,
or to an end-of-file.
If any
character of
word
is quoted
(see ``Quoting''),
no additional processing is done to the shell input.
If no characters of
word
are quoted:
-
parameter and command substitution occurs,
-
(escaped)
\newlines are removed, and
-
\
must be used to quote the characters
\,
$,
and
`.
The resulting document becomes
the standard input.
<&digit-
Use the file associated with file descriptor
digit
as standard input.
Similarly for the standard output using
>&digit.
<&--
The standard input is closed.
Similarly for 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 associated
with
file descriptor 1.
The order in which redirections are specified is significant.
The shell evaluates redirections left-to-right.
For example:
... 1>xxx 2>&1
first associates file descriptor 1 with file
xxx.
It associates file descriptor 2 with the file associated with
file
descriptor 1 (that is,
xxx).
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
xxx.
Using the terminology introduced on the first page, under
Commands,
if a command
is composed of several simple-commands,
redirection will be evaluated for the entire command
before it is evaluated for each simple-command.
That is, the shell evaluates redirection
for the entire list,
then each pipeline within the list,
then each command within each pipeline,
then each list within each command.
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.
Redirection of output is not allowed in the restricted shell.
Filename generation
Before a command is executed,
each command word
is scanned for
the characters
*,
?,
and
[.
If one of these characters appears
the word is regarded as a
pattern.
The word is replaced with alphabetically sorted filenames that
match the pattern.
If no filename is found that matches the pattern,
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.
*-
Matches any string, including supplementary code set
characters and the null string.
?-
Matches any single character, including supplementary code set
characters.
[...]-
Matches any one character in the string enclosed by square
brackets, or any one character with a code value within the range
designated using a minus (-) sign,
including supplementary code set characters.
When the characters in the range are from different code sets,
one of the characters
specifying the range is matched.
If the first character following the opening
[
is a
!,
any character not enclosed is matched,
including supplementary code set characters.
NOTE:
All quoted characters (see below) must
be matched explicitly in a filename.
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
backslash (\) or inserting it between a pair of quote
marks
('' or "").
During processing,
the shell may quote certain characters to prevent them from
taking on
a special meaning.
Backslashes used to quote a single character are removed from the
word before
the command is executed.
The pair
\newline
is removed from a word before command and parameter substitution.
All characters enclosed between a pair of single quote marks
(''),
except a single quote,
are quoted by the shell.
Backslash has no special meaning inside a pair of single quotes.
A single quote may be quoted inside a pair of double quote marks
(for example, "'"),
but a single quote can not be quoted inside a pair of single
quotes.
Inside a pair of double quote marks
(""),
parameter and command substitution occurs and
the shell quotes the results to avoid blank interpretation and
filename
generation.
If
$*
is within a pair of double quotes,
the positional parameters are substituted and quoted,
separated by quoted spaces
("$1 $2 ...");
however,
if
$@
is within a pair of double quotes,
the positional parameters are substituted and quoted,
separated by unquoted spaces
("$1" "$2" ... ).
\
quotes the characters
\,
`,
",
and
$.
The pair
\newline
is removed before parameter and command substitution.
If a backslash precedes characters other than
\,
`,
",
$,
and
newline, then the backslash itself is quoted by the shell.
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.
Defaults
The file /etc/default/sh
(which does not exist by default)
can contain a value
for the parameter TIMEOUT; this integer value
specifies the number of seconds that can elapse
without user activity before a shell will exit.
If this value is 0, undefined, or the file
/etc/default/sh does not exist (the default),
the shell will wait for user input
until explicitly terminated.
Environment
The
environment
(see
environ(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
command is used to bind the shell's
parameter
to the environment (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 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:
TERM=450 cmd
and
(export TERM; TERM=450; cmd)
are equivalent as far as the execution of
cmd
is concerned if
cmd
is not a ``special command''
(see ``Special commands'').
If
cmd
is a special command, then
TERM=450 cmd
will modify the TERM variable in the current shell.
If the
-k
flag is set,
all
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
When a command is run
in the background (cmd &) under sh,
it can receive interrupt (SIGINT) and quit (SIGQUIT) signals
but ignores them by default.
(A background process
can override this default behavior
via trap or signal.
For details,
see the description of trap, below,
or
signal(2).)
When a command is run
in the background under jsh, however,
it does not receive interrupt or quit signals.
Otherwise
signals have
the values inherited by the shell from its parent,
with the exception of three signals:
11 (SIGSEV), 14 (SIGALARM),
and 18 (SIGCHILD).
Execution
Each time a command is executed,
the command substitution,
parameter substitution,
blank interpretation,
input/output redirection, and filename generation
listed above are carried out.
If the command name 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).
If the command name does not match the name of a defined
function,
but matches one of the special commands
listed below in Special Commands, it is executed in the shell process.
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(2).
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
/usr/bin:.
The current directory is specified by a null path name,
which can appear immediately after the equal sign,
between two colon delimiters anywhere in the path list,
or at the end of the path list.
If the command name contains a / 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 has execute permission but is not an
a.out
file,
it is assumed to be a file containing shell commands.
A sub-shell is spawned to read it.
A parenthesized command is also executed in
a sub-shell.
For shell script files, in order for the
``set user ID on execution''
and/or the
``set group ID on execution''
mode to be effective,
the first line of the file must be
#! /sbin/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 below).
Special commands
Input/output redirection is now permitted for these commands.
File descriptor 1 is the default output location.
When job control is enabled, additional special commands
are added to the
shell's environment (see ``Job control'').
:-
No effect; the command does nothing.
A zero exit code is returned.
. file-
Read and execute commands from
file
and return.
The search path
specified by
PATH
is used to find the directory containing
file.
break [n]-
Exit from the enclosing for or
while
loop, if any.
If
n
is specified, break
n
levels.
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 [arg]-
Change 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:
The current directory is specified 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
arg
begins with a / the search path
is not used.
Otherwise, each directory in the path is
searched for
arg.
The
cd
command may not be executed by
/usr/lib/rsh.
echo [arg ... ]-
Echo arguments.
See
echo(1)
for usage and description.
eval [arg ... ]-
The arguments are read as input
to the shell
and the resulting command(s) executed.
exec [arg ... ]-
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 the shell to exit.)
export [name ... ]-
The given
names
are marked
for automatic export to the
``environment''
of subsequently executed commands.
If no arguments are given,
variable names that have been marked for export during the
current shell's execution
are listed.
(Variable names exported from a parent shell are listed only if
they
have been exported again during the current shell's execution.)
Function names are
not
exported.
getopts-
Use in shell scripts to
support command syntax standards (see
intro(1));
it parses positional parameters and checks for legal options.
See
getopts(1)
for usage and description.
hash [ -r] [name ... ]-
For each
name,
the location in the search path of the command specified by
name
is determined and remembered by the shell.
The
-r
option causes the shell to forget all remembered locations.
If no arguments are given, ``hits'' and ``cost'' 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.
If a command is found in a relative directory in the search
path,
after changing to that directory,
the stored location
of that command is 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.
newgrp [arg ]-
Equivalent to
exec newgrp arg.
See
newgrp(1M)
for usage and description.
priv [ +|-priv_name . . . ] set_name [ . . . ]-
For each set_name,
priv sets or displays the privileges
contained in that privilege set.
set_name may be either ``max'' for the
maximum privilege set or ``work'' for the working set.
priv_name is the name of a privilege.
If priv_names are
supplied, priv scans the list and turns off thoses
privileges
that are preceded by a minus sign and turns on those that are
preceded
by a plus sign in each of the sets listed.
If no priv_names are supplied, the priv command
prints
the current list of privileges for each of the requested sets.
The values for priv_name are:
allprivs-
Represents all possible privileges.
audit-
Required to manipulate the security audit mechanisms.
auditwr-
Required to write miscellaneous audit records to the audit trail.
compat-
Overrides specific restrictions that are imposed solely for the
confinement of covert channels.
core-
Required to dump a core image of a process that is either privileged,
setuid, or setgid.
This privilege is not required to dump the core image of a process that
does not meet the above conditions.
dacread-
Overrides Discretionary Access Control (DAC) restrictions but only for
operations that do not alter objects (that is, read and execute
permissions).
See ``Access permissions'' below.
dacwrite-
Overrides Discretionary Access Control restrictions but only for
operations that alter objects (that is, write permission).
See ``Access permissions'' below.
dev-
Currently unused.
driver-
Provides compatibility with device drivers developed by third party vendors.
It is used when a sensitive operation needs to be limited to a privileged process.
filesys-
Required for privileged operations on a file system that have relatively
low sensitivity, including the creation of links to directories, setting
the effective root directory, and making special files.
fsysrange-
Override file system range restrictions.
loadmod-
Required to perform selective operations associated with loadable modules.
macread-
Currently unused.
macwrite-
Currently unused.
macupgrade-
Currently unused.
mount-
Mount or unmount a file system.
multidir-
Currently unused.
owner-
Required to change the attributes of a file (that is, information kept
in the file's inode)
that is not owned by the effective uid of the calling process.
See ``Access permissions'' below.
plock-
Required to lock a process in memory.
setflevel-
Currently unused.
setplevel-
Currently unused.
setspriv-
Administrative privilege required to set the inheritable and fixed
privileges on files.
This privilege overrides access and ownership restrictions.
setuid-
Required in order to set the real and effective user and group
ID
of a process.
setupriv-
Privilege required for an otherwise unprivileged process to set the
inheritable and fixed privileges on a file.
This privilege does not override
access or ownership restrictions.
sysops-
Required to perform several general system operations that have only
minor security implications.
tshar-
Required to raise the priority of a time sharing process or to set
the user priority limit to a value greater than 0.
rtime-
Required by processes that do real-time operations.
Access Permissions:
-
Access permissions are associated with the priv_name entries.
-
Access checking is performed whenever a subject (such as a process)
tries to access an object (such as a file or directory).
Permission to access an object is granted or denied on the basis of
mode bits and Access Control Lists (ACLs);
ACLs and mode bits are collectively known as Discretionary Access Control (DAC).
-
The
standard file access permission bit checks are performed to determine if the
process requesting access to the object has permission to access it
in the manner (read, write, and/or execute/search) requested.
Each access mode requested is checked separately using the following
algorithm:
-
If the effective
user
ID
of the process is equal to the user
ID
of the owner of the
file, and the requested access mode bit is set in the
``owner''
bits of the mode, access is granted;
otherwise access checking continues.
-
If the effective user
ID
of the process matches the user
ID
in a
``user''
ACL entry,
and the requested access mode bit is set in the
``group''
bits of the mode and in the matching ACL entry, access is granted;
otherwise, or if no ACL is present, access checking continues.
-
If the effective group ID (or any of the supplementary
group ID of the process) matches the group ID
specified in any ``group''
ACL entry (or the owning group of the file, if no ACL is present),
and the requested access mode bit is set in the ``group'' bits of the
mode and in the matching ACL entry, access is granted;
otherwise, access checking continues.
-
If the above checks fail, and the requested access mode bit is set
in the ``other'' bits of the mode, access is granted;
otherwise, access is denied (EACCES is returned).
(Note that if a process's user ID matches a ``user''
ACL entry and the group ID matches one or more
``group'' entries, only the ``user'' ACL entry is used to determine access.)
-
These checks are performed
on every component of the pathname, including the object itself.
If any of the checks fail,
the privileges of the calling process are examined to determine
if the calling process has the
appropriate privilege for the mode requested
(dacread for read and execute/search access,
dacwrite for write access).
Example:
This example adds owner and audit privileges
and deletes dacread privilege from the working set:
priv +owner +audit -dacread work
pwd-
Print the current working directory.
See
pwd(1)
for usage and description.
read [-r] name ...-
One line is read from the standard input and,
using the internal field separator,
IFS,
to delimit word boundaries,
the first
word is assigned to the first
name,
the second word
to the second
name,
etc., with leftover words assigned to the last
name.
If -r is not specified,
lines
can be continued using
\newline and
characters other than
newline
can be quoted by preceding them with a backslash.
These backslashes are removed before words are assigned to
names,
and no interpretation is done on the character that follows the
backslash.
If -r is specified, backslashes are treated as normal
characters, so are not removed from the input, nor do they affect the
next character.
The return code is 0, unless an end-of-file is encountered.
readonly [name ... ]-
The given
names
are marked readonly
and
the values of the these
names
may not be changed
by subsequent assignment.
If no arguments are given, a list
of all readonly
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 [ --aefhkntuvx [arg ... ] ]-
-a-
Mark variables which are modified or created for export.
-e-
Exit immediately if a command
exits with a non-zero exit status.
-f-
Disable filename generation.
-h-
Locate and remember function commands as functions are defined
(function commands are normally located when the function is
executed).
-k-
All keyword arguments are placed in the environment for a
command,
not just those that precede the command name.
-n-
Read commands but do not execute them.
-t-
Exit after reading and executing one command.
-u-
Treat unset variables as an error when substituting.
-v-
Print shell input lines as they are read.
-x-
Print commands and their arguments as they are executed.
---
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.
test-
Evaluate conditional expressions.
See
test(1)
for usage and description.
times-
Print the accumulated user and system times for processes
run from the shell.
trap [arg] [n] ...-
The command
arg
is to be read and executed when the shell
receives,
n,
numeric or symbolic signal(s).
NOTE:
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 or
corresponding symbolic
names.
Any attempt to set a trap on a signal that
was ignored on entry to the current shell
is ineffective.
An error results when an attempt is made
to trap on any of the following three signals:
-
signal 11 (SIGSEV--segmentation fault);
-
signal 14 (SIGALRM--alarm clock);
-
signal 18 (SIGCHILD--child status changed).
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 ... ]-
For each
name,
indicate how it would be interpreted if used as a command name.
ulimit [ -[HS][a | cdfnstv] ]-
ulimit [ -[HS][c | d | f | n | s | t | v] ] limit-
ulimit
prints or sets hard or soft resource limits.
These limits are described in
getrlimit(2).
If
limit
is not present,
ulimit
prints the specified limits.
Any number of limits may be printed at one time.
The
-a
option prints all limits.
If
limit
is present,
ulimit
sets the specified limit to
limit.
The string
``unlimited''
requests the largest valid limit.
Limits may be set for only one resource at a time.
Any user may set a soft limit to any value below the hard limit.
Any user may lower a hard limit.
Only a privileged user may raise a hard limit.
The
-H
option specifies a hard limit.
The
-S
option specifies a soft limit.
If neither option is specified,
ulimit will set both limits and print the
soft limit.
The following options specify the resource whose limits are to be
printed or set.
If no option is specified, the file size limit is printed or set.
-c-
maximum core file size (in 512-byte blocks)
-d-
maximum size of data segment or heap (in kbytes)
-f-
maximum file size (in 512-byte blocks)
-n-
maximum file descriptor plus 1
-s-
maximum size of stack segment (in kbytes)
-t-
maximum CPU time (in seconds)
-v-
maximum size of virtual memory (in kbytes)
umask [ -S ] [mask]-
The user file-creation mask is set
by
mask.
If
mask
is omitted, the current value of the mask is printed.
If -S is specified, the mask is printed in symbolic form,
otherwise it is printed
in octal form.
See
umask(1)
for further details.
unset [name ... ]-
For each
name,
remove the corresponding variable or function value.
The variables
PATH, PS1, PS2,
MAILCHECK, and IFS
cannot be unset.
wait [pid ... ]-
Wait for your background processes whose process
IDs are the values of
pid
and return the termination status of
the final
pid.
If
pid
is omitted,
all your shell's currently active background processes are waited
for
and the return code will be zero.
See
wait(1)
for further details.
Invocation
If the shell is invoked through
exec(2)
and the first character of argument zero
is
-,
commands are initially read from
/etc/profile
and 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
/usr/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.
-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 SIGTERM is ignored (so that kill 0
does not kill an interactive shell) and SIGINT is
caught and ignored
(so that
wait
is interruptible).
In all cases, SIGQUIT is ignored by the shell.
-p-
If the -p flag is present, the shell will not set the
effective user
and group IDs to the real user and group IDs.
If the -p flag is not present, the shell will set the
effective user ID to the real user ID if the effective user ID is <100,
and the shell will set the
effective group ID to the real group ID
if the effective group ID is <100 and not equal to 1.
-r-
If the
-r
flag is present the shell is a restricted shell.
-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 special commands)
is written to file descriptor 2.
The remaining flags and arguments are described under the
set
command above.
Job control (jsh)
When the shell is invoked as jsh,
job control is enabled
in addition to all of the functionality described previously for
sh.
Typically job control is enabled for the interactive shell only.
Non-interactive shells typically do not benefit from the added
functionality
of job control.
With job control enabled every command or pipeline the user
enters at
the terminal is called a ``job''.
All jobs exist in one of the
following states: foreground, background or stopped.
These terms are defined as follows:
-
a job in the foreground has read and write access to the
controlling terminal;
-
a job in the background is denied read access and has
conditional write access to the
controlling terminal (see
stty(1));
-
a stopped job is a job that has been placed in a suspended
state,
usually as a result of a SIGTSTP signal
(see
signal(5)).
Jobs in the foreground can be stopped
by interrupt (SIGINT) or quit (SIGQUIT) signals from the keyboard;
background jobs cannot be stopped by these signals.
Every job that the
shell starts is assigned a positive integer, called a ``job number''
that is tracked by the shell and is used as an identifier
for a specific job.
Additionally, the shell keeps track of the
``current'' and ``previous'' jobs.
The current job is the
most recent job to be started or restarted.
The previous job is
the first non-current job.
The acceptable syntax for a Job Identifier is of the form:
%jobid
where jobid may be specified in any of the following
formats:
% or +-
for the current job
--
for the previous job
?<string>-
specify the job for which the command line uniquely contains
string.
n-
for job number n, where n is a job number
pref-
where pref is a
unique prefix of the command name (for example, if the command
ls -l foo were running in the background, it
could be referred to as %ls); pref cannot
contain blanks
unless it is quoted.
When job control is enabled,
the following commands are
added to the user's environment to manipulate jobs:
bg [%jobid ...]-
Resumes the execution of a stopped job in
the background.
If %jobid is omitted the current job is assumed.
fg [%jobid ...]-
Resumes the execution of a stopped
job in the foreground, also
moves an executing background job into the foreground.
If %jobid is omitted the current job is assumed.
jobs [-p|-l] [%jobid . . .]-
jobs -x command [arguments]-
Reports all jobs that are stopped or
executing in the background.
If %jobid is omitted, all jobs that
are stopped or running in the background will be reported.
The following
options will modify/enhance the output of jobs:
-l-
Report the process group ID and working directory of the
jobs.
-p-
Report only the process group ID of the jobs.
-x-
Replace any jobid found in command or arguments with
the corresponding process group ID, and then execute
command passing
it arguments.
kill [-s signal] %jobid ...-
kill -l [status]-
kill [-signal] %jobid ...-
Builtin version of kill to provide the functionality of the
kill(1)
command for processes identified with a jobid.
See
kill(1)
for the other functionality.
stop %jobid ...-
Stops the execution of a background job(s).
suspend-
Stops the execution of the current shell (but not if it is the
login
shell).
wait [%jobid ...]-
wait builtin accepts a job identifier.
If
%jobid is omitted wait behaves as described
above
under Special Commands.
Restricted shell (/usr/lib/rsh) only
/usr/lib/rsh
is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard
shell.
The actions of
/usr/lib/rsh
are identical to those of
sh,
except that the following are disallowed:
-
changing directory (see
cd(1))
-
setting the value of
$PATH
-
specifying path or
command names containing
/
-
redirecting output
(>
and
>>)
The restrictions above are enforced
after .profile is interpreted.
A restricted shell can be invoked in one of the following ways:
-
rsh
is the filename part of the last entry in the
/etc/passwd
file
(see
passwd(4));
-
the environment variable
SHELL
exists and
rsh
is the filename part of its value;
-
the shell is invoked and
rsh
is the filename part of argument 0;
-
the shell is invoked with the
-r
option.
When a command to be executed is found to be a shell procedure,
/usr/lib/rsh
invokes
sh
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
(see
profile(4))
has complete control over user actions
by performing guaranteed setup actions
and leaving the user in an appropriate directory
(probably
not
the login directory).
The system administrator often sets up a directory
of commands
(for example,
/usr/rbin)
that can be safely invoked by
a restricted shell.
Some systems also provide a restricted editor,
red.
Files
/etc/profile-
$HOME/.profile-
/tmp/sh*-
/dev/null-
/usr/lib/locale/locale/LC_MESSAGES/uxcore.abi-
language-specific message file (see LANG on
environ(5)).
Exit codes
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).
jsh only
If the shell is invoked as jsh and an attempt is made to
exit
the shell while there are stopped jobs, the shell issues one
warning:
there are stopped jobs
This is the only message.
If another exit attempt is made, and there are
still stopped jobs they will be sent a SIGHUP signal from
the kernel
and the shell is exited.
References
cd(1),
dup(2),
echo(1),
environ(5),
exec(2),
fork(2),
getopts(1),
getrlimit(2),
intro(1),
intro(2),
ksh88(1),
ksh(1),
login(1),
newgrp(1M),
pipe(2),
profile(4),
pwd(1),
setlocale(3C),
signal(5),
stty(1),
test(1),
ulimit(2),
umask(1),
wait(1)
Notices
Words used for filenames in input/output redirection
are not interpreted for filename generation
(see ``Filename generation'', above).
For example,
cat file1 >a*
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 UX:sh:ERROR:cannot fork, too
many processes
, try using the
wait(1)
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 process ids
associated with your login,
and to the number the system can keep track of.)
Only the last process in a pipeline can be waited for.
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
exec
the original command.
Use the
hash
command to correct this situation.
Prior to Release 4, the rsh command invoked the restricted shell.
This restricted shell command is /usr/lib/rsh and it can be
executed by using the full pathname.
Beginning with Release 4, the rsh command is the remote shell
(see
rsh(1tcp)).
POSIX.2 states that assignments are performed from
the beginning of the command text to the end.
Therefore, the order of evaluation for variable assignments
is changed to use left to right expansion rules.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004