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517.

Trap signals and other events.

Defines and activates handlers to be run when the shell receives signals
or other conditions.

ARG is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC. If ARG is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value. If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes.

If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell. If
a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command. If
a SIGNAL_SPEC is RETURN, ARG is executed each time a shell function or a
script run by the . or source builtins finishes executing. A SIGNAL_SPEC
of ERR means to execute ARG each time a command's failure would cause the
shell to exit when the -e option is enabled.

If no arguments are supplied, trap prints the list of commands associated
with each signal.

Options:
-l[tab]print a list of signal names and their corresponding numbers
-p[tab]display the trap commands associated with each SIGNAL_SPEC

Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
Signal names are case insensitive and the SIG prefix is optional. A
signal may be sent to the shell with "kill -signal $$".

Exit Status:
Returns success unless a SIGSPEC is invalid or an invalid option is given.

518.

Display information about command type.

For each NAME, indicate how it would be interpreted if used as a
command name.

Options:
-a[tab]display all locations containing an executable named NAME;
[tab]includes aliases, builtins, and functions, if and only if
[tab]the `-p' option is not also used
-f[tab]suppress shell function lookup
-P[tab]force a PATH search for each NAME, even if it is an alias,
[tab]builtin, or function, and returns the name of the disk file
[tab]that would be executed
-p[tab]returns either the name of the disk file that would be executed,
[tab]or nothing if `type -t NAME' would not return `file'.
-t[tab]output a single word which is one of `alias', `keyword',
[tab]`function', `builtin', `file' or `', if NAME is an alias, shell
[tab]reserved word, shell function, shell builtin, disk file, or not
[tab]found, respectively

Arguments:
NAME[tab]Command name to be interpreted.

Exit Status:
Returns success if all of the NAMEs are found; fails if any are not found.

519.

Modify shell resource limits.

Provides control over the resources available to the shell and processes
it creates, on systems that allow such control.

Options:
-S[tab]use the `soft' resource limit
-H[tab]use the `hard' resource limit
-a[tab]all current limits are reported
-b[tab]the socket buffer size
-c[tab]the maximum size of core files created
-d[tab]the maximum size of a process's data segment
-e[tab]the maximum scheduling priority (`nice')
-f[tab]the maximum size of files written by the shell and its children
-i[tab]the maximum number of pending signals
-l[tab]the maximum size a process may lock into memory
-m[tab]the maximum resident set size
-n[tab]the maximum number of open file descriptors
-p[tab]the pipe buffer size
-q[tab]the maximum number of bytes in POSIX message queues
-r[tab]the maximum real-time scheduling priority
-s[tab]the maximum stack size
-t[tab]the maximum amount of cpu time in seconds
-u[tab]the maximum number of user processes
-v[tab]the size of virtual memory
-x[tab]the maximum number of file locks

If LIMIT is given, it is the new value of the specified resource; the
special LIMIT values `soft', `hard', and `unlimited' stand for the
current soft limit, the current hard limit, and no limit, respectively.
Otherwise, the current value of the specified resource is printed. If
no option is given, then -f is assumed.

Values are in 1024-byte increments, except for -t, which is in seconds,
-p, which is in increments of 512 bytes, and -u, which is an unscaled
number of processes.

Exit Status:
Returns success unless an invalid option is supplied or an error occurs.

520.

Display or set file mode mask.

Sets the user file-creation mask to MODE. If MODE is omitted, prints
the current value of the mask.

If MODE begins with a digit, it is interpreted as an octal number;
otherwise it is a symbolic mode string like that accepted by chmod(1).

Options:
-p[tab]if MODE is omitted, output in a form that may be reused as input
-S[tab]makes the output symbolic; otherwise an octal number is output

Exit Status:
Returns success unless MODE is invalid or an invalid option is given.

521.

Wait for job completion and return exit status.

Waits for the process identified by ID, which may be a process ID or a
job specification, and reports its termination status. If ID is not
given, waits for all currently active child processes, and the return
status is zero. If ID is a a job specification, waits for all processes
in the job's pipeline.

Exit Status:
Returns the status of ID; fails if ID is invalid or an invalid option is
given.

522.

Wait for process completion and return exit status.

Waits for the specified process and reports its termination status. If
PID is not given, all currently active child processes are waited for,
and the return code is zero. PID must be a process ID.

Exit Status:
Returns the status of ID; fails if ID is invalid or an invalid option is
given.

523.

Execute commands for each member in a list.

The `for' loop executes a sequence of commands for each member in a
list of items. If `in WORDS ...;' is not present, then `in "$@"' is
assumed. For each element in WORDS, NAME is set to that element, and
the COMMANDS are executed.

Exit Status:
Returns the status of the last command executed.

524.

Arithmetic for loop.

Equivalent to
[tab](( EXP1 ))
[tab]while (( EXP2 )); do
[tab][tab]COMMANDS
[tab][tab](( EXP3 ))
[tab]done
EXP1, EXP2, and EXP3 are arithmetic expressions. If any expression is
omitted, it behaves as if it evaluates to 1.

Exit Status:
Returns the status of the last command executed.

525.

Select words from a list and execute commands.

The WORDS are expanded, generating a list of words. The
set of expanded words is printed on the standard error, each
preceded by a number. If `in WORDS' is not present, `in "$@"'
is assumed. The PS3 prompt is then displayed and a line read
from the standard input. If the line consists of the number
corresponding to one of the displayed words, then NAME is set
to that word. If the line is empty, WORDS and the prompt are
redisplayed. If EOF is read, the command completes. Any other
value read causes NAME to be set to null. The line read is saved
in the variable REPLY. COMMANDS are executed after each selection
until a break command is executed.

Exit Status:
Returns the status of the last command executed.

526.

Report time consumed by pipeline's execution.

Execute PIPELINE and print a summary of the real time, user CPU time,
and system CPU time spent executing PIPELINE when it terminates.

Options:
-p[tab]print the timing summary in the portable Posix format

The value of the TIMEFORMAT variable is used as the output format.

Exit Status:
The return status is the return status of PIPELINE.