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Unset values and attributes of shell variables and functions.

For each NAME, remove the corresponding variable or function.

Options:
-f[tab]treat each NAME as a shell function
-v[tab]treat each NAME as a shell variable
-n[tab]treat each NAME as a name reference and unset the variable itself
[tab][tab]rather than the variable it references

Without options, unset first tries to unset a variable, and if that fails,
tries to unset a function.

Some variables cannot be unset; also see ‘readonly’.

Exit Status:
Returns success unless an invalid option is given or a NAME is read-only.

Set export attribute for shell variables.

Marks each NAME for automatic export to the environment of subsequently
executed commands. If VALUE is supplied, assign VALUE before exporting.

Options:
-f[tab]refer to shell functions
-n[tab]remove the export property from each NAME
-p[tab]display a list of all exported variables and functions

An argument of ‘--’ disables further option processing.

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

Mark shell variables as unchangeable.

Mark each NAME as read-only; the values of these NAMEs may not be
changed by subsequent assignment. If VALUE is supplied, assign VALUE
before marking as read-only.

Options:
-a[tab]refer to indexed array variables
-A[tab]refer to associative array variables
-f[tab]refer to shell functions
-p[tab]display a list of all readonly variables or functions,
[tab][tab]depending on whether or not the -f option is given

An argument of ‘--’ disables further option processing.

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

Shift positional parameters.

Rename the positional parameters $N+1,$N+2 ... to $1,$2 ... If N is
not given, it is assumed to be 1.

Exit Status:
Returns success unless N is negative or greater than $#.

Execute commands from a file in the current shell.

Read and execute commands from FILENAME in the current shell. The
entries in $PATH are used to find the directory containing FILENAME.
If any ARGUMENTS are supplied, they become the positional parameters
when FILENAME is executed.

Exit Status:
Returns the status of the last command executed in FILENAME; fails if
FILENAME cannot be read.

Suspend shell execution.

Suspend the execution of this shell until it receives a SIGCONT signal.
Unless forced, login shells cannot be suspended.

Options:
-f[tab]force the suspend, even if the shell is a login shell

Exit Status:
Returns success unless job control is not enabled or an error occurs.

Evaluate conditional expression.

Exits with a status of 0 (true) or 1 (false) depending on
the evaluation of EXPR. Expressions may be unary or binary. Unary
expressions are often used to examine the status of a file. There
are string operators and numeric comparison operators as well.

The behavior of test depends on the number of arguments. Read the
bash manual page for the complete specification.

File operators:

-a FILE True if file exists.
-b FILE True if file is block special.
-c FILE True if file is character special.
-d FILE True if file is a directory.
-e FILE True if file exists.
-f FILE True if file exists and is a regular file.
-g FILE True if file is set-group-id.
-h FILE True if file is a symbolic link.
-L FILE True if file is a symbolic link.
-k FILE True if file has its ‘sticky’ bit set.
-p FILE True if file is a named pipe.
-r FILE True if file is readable by you.
-s FILE True if file exists and is not empty.
-S FILE True if file is a socket.
-t FD True if FD is opened on a terminal.
-u FILE True if the file is set-user-id.
-w FILE True if the file is writable by you.
-x FILE True if the file is executable by you.
-O FILE True if the file is effectively owned by you.
-G FILE True if the file is effectively owned by your group.
-N FILE True if the file has been modified since it was last read.

FILE1 -nt FILE2 True if file1 is newer than file2 (according to
modification date).

FILE1 -ot FILE2 True if file1 is older than file2.

FILE1 -ef FILE2 True if file1 is a hard link to file2.

String operators:

-z STRING True if string is empty.

-n STRING
STRING True if string is not empty.

STRING1 = STRING2
True if the strings are equal.
STRING1 != STRING2
True if the strings are not equal.
STRING1 < STRING2
True if STRING1 sorts before STRING2 lexicographically.
STRING1 > STRING2
True if STRING1 sorts after STRING2 lexicographically.

Other operators:

-o OPTION True if the shell option OPTION is enabled.
-v VAR True if the shell variable VAR is set.
-R VAR True if the shell variable VAR is set and is a name
reference.
! EXPR True if expr is false.
EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.

arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.

Arithmetic binary operators return true if ARG1 is equal, not-equal,
less-than, less-than-or-equal, greater-than, or greater-than-or-equal
than ARG2.

Exit Status:
Returns success if EXPR evaluates to true; fails if EXPR evaluates to
false or an invalid argument is given.

Evaluate conditional expression.

This is a synonym for the “test” builtin, but the last argument must
be a literal ‘]’, to match the opening ‘[’.

Display process times.

Prints the accumulated user and system times for the shell and all of its
child processes.

Exit Status:
Always succeeds.

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.