Comenzi interne (builtin) de bash

Aici sunt prezentate comenzile interne (builtin) ale shell-ului bash, cu textele originale care sunt afisate de comanda help. In acest fisier gasesti o lista cu descrierea sumara a comenzilor, dar daca dai click pe numele comenzii esti transportat mai jos in fisier, la descrierea ei detaliata.

% - reia un proces stopat sau din background, ca si comanda fg
. - citeste si executa comenzi dintr-un fisier, si revine in shell
: - comanda fara efect, intoarce codul 0 de iesire
alias - afiseaza sau defineste aliasuri de shell
bg - lanseaza un proces in background
bind - asigneaza combinatii de taste unei functii sau unei macroinstructiuni
break - iese din cicluri for, until sau while
builtin - lanseaza o comanda din setul de comenzi builtin
case - executa comenzi in mod selectiv
cd - schimba directorul curent de lucru
command - executa o comanda cu argumentele, ignor'nd functiile de shell
continue - continua cu urmatoarea iteratie dintr-un ciclu for, until sau while
declare - declara si seteaza variabile de shell
dirs - afiseaza lista directoarelor din stiva de directoare
echo - scrie la iesire argumentele
enable - activeaza si dezactiveaza comenzi builtin ale shellului
eval - evalueaza argumentele si executa comanda rezultata
exec - executa un fisier intr-un shell specificat in fisier
exit - iese din shell-ul curent
export - exporta variabile in shell-ul parinte
fc - compara fisiere, rand cu rand
fg - aduce in foreground un proces care ruleaza in background
for - executa un ciclu cu un numar specificat de iteratii
function - creeaza o comanda simpla care poate fi invocata prin numele ei
getopts - folosita de proceduri de shell la separarea parametrilor comenzilor pentru interpretare
hash - face shell-ul sa 'uite' sau sa-si 'reaminteasca' locatii ale comenzilor
help - afiseaza instructiuni sumare despre comenzile builtin
history - afiseaza comenzile din istoric, numerotate
if - permite executia conditionata a comenzilor
jobs - afiseaza joburile active din sistem
kill - trimite unui job un semnal specificat
let - evalueaza expresii si atribuie valori variabilelor
local - creeaza o variabila locala si ii atribuie o valoare
logout - iese din shell-ul de login curent
popd - sterge elemente din stiva de directoare
pushd - introduce elemente in stiva de directoare
pwd - afiseaza directorul curent de lucru
read - citeste date de la intrarea standard si le atribuie ca valori
readonly - marcheaza entitati de shell ca read-only
return - iese dintr-o functie
select - executa comenzi in functie de cuvinte selectate de la tastatura
set - seteaza si manipuleaza variabilele de mediu
shift - deplaseaza parametrii pozitionali dintr-o comanda
source - citeste si executa comenzi dintr-un fisier, apoi revine in shell
suspend - suspenda executia shell-ului curent pana la primirea unui semnal de continuare
test - testeaza o expresie logica (intoarce 0 sau 1)
times - afiseaza timpul acumulat de utilizator si de sistem in shell-ul curent
trap - executa comenzi in functie de semnalele interceptate
type - afiseaza modul cum ar fi interpretat un nume daca ar fi folosit ca o comanda
typeset - comanda depasita (vezi declare)
ulimit - controleaza resursele disponibile pentru procesele lansate de shell
umask - defineste un model de drepturi de acces, aplicat fisierelor nou create de utilizator
unalias - sterge aliasuri din sistem
unset - sterge variabile de mediu sau functii din sistem
until - repeta un ciclu pana la indeplinirea unei conditii
variables - afiseaza o lista a variabilelor de mediu cu explicarea lor
while - repeta un ciclu atata vreme cat este indeplinita o conditie

%: %[DIGITS | WORD] [&]
This is similar to the `fg' command. Resume a stopped or background
job. If you specifiy DIGITS, then that job is used. If you specify
WORD, then the job whose name begins with WORD is used. Following the
job specification with a `&' places the job in the background.

.: . filename
Read and execute commands from FILENAME and return. The pathnames
in $PATH are used to find the directory containing FILENAME.

No effect; the command does nothing. A zero exit code is returned.

alias

alias: alias [ name[=value] ]
`alias' with no arguments prints the list of aliases in the form
NAME=VALUE on standard output. An alias is defined for each NAME
whose VALUE is given. A trailing space in VALUE causes the next
word to be checked for alias substitution. Alias returns true
unless a NAME is given for which no alias has been defined.

bg

bg: bg [job_spec]
Place JOB_SPEC in the background, as if it had been started with
`&'. If JOB_SPEC is not present, the shell's notion of the current
job is used.

bind

bind: bind [-lvd] [-m keymap] [-f filename] [-q name] [keyseq:readline-function]
Bind a key sequence to a Readline function, or to a macro. The
syntax is equivalent to that found in ~/.inputrc, but must be
passed as a single argument: bind ''C-xC-r': re-read-init-file'.
Arguments we accept:
-m keymap Use `keymap' as the keymap for the duration of this
command. Acceptable keymap names are emacs,
emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move,
vi-command, and vi-insert.
-l List names of functions.
-v List function names and bindings.
-d Dump functions and bindings such that they
can be read back in.
-f filename Read key bindings from FILENAME.
-q function-name Query about which keys invoke the named function.

break

break: break [n]
Exit from within a FOR, WHILE or UNTIL loop. If N is specified,
break N levels.

builtin

builtin: builtin [shell-builtin [arg ]]
Run a shell builtin. This is useful when you wish to rename a
shell builtin to be a function, but need the functionality of the
builtin within the function itself.

case

case: case WORD in [PATTERN [| PATTERN]) COMMANDS ;;] esac
Selectively execute COMMANDS based upon WORD matching PATTERN. The
`|' is used to separate multiple patterns.

cd

cd: cd [dir]
Change the current directory to DIR. The variable $HOME is the
default DIR. The variable $CDPATH defines the search path for
the directory containing DIR. Alternative directory names are
separated by a colon (:). A null directory name is the same as
the current directory, i.e. `.'. If DIR begins with a slash (/),
then $CDPATH is not used. If the directory is not found, and the
shell variable `cdable_vars' exists, then try the word as a variable
name. If that variable has a value, then cd to the value of that
variable.

command

command: command [-pVv] [command [arg ]]
Runs COMMAND with ARGS ignoring shell functions. If you have a shell
function called `ls', and you wish to call the command `ls', you can
say 'command ls'. If the -p option is given, a default value is used
for PATH that is guaranteed to find all of the standard utilities. If
the -V or -v option is given, a string is printed describing COMMAND.
The -V option produces a more verbose description.

continue

continue: continue [n]
Resume the next iteration of the enclosing FOR, WHILE or UNTIL loop.
If N is specified, resume at the N-th enclosing loop.

declare

declare: declare [-[frxi]] name[=value]
Declare variables and/or give them attributes. If no NAMEs are
given, then display the values of variables instead.

The flags are:

-f to select from among function names only,
-r to make NAMEs readonly,
-x to make NAMEs export,
-i to make NAMEs have the `integer' attribute set.

Variables with the integer attribute have arithmetic evaluation (see
`let') done when the variable is assigned to.

Using `+' instead of `-' turns off the given attribute instead. When
used in a function, makes NAMEs local, as with the `local' command.

dirs

dirs: dirs [-l]
Display the list of currently remembered directories. Directories
find their way onto the list with the `pushd' command; you can get
back up through the list with the `popd' command.

The -l flag specifies that `dirs' should not print shorthand versions
of directories which are relative to your home directory. This means
that `~/bin' might be displayed as `/homes/bfox/bin'.

echo

echo: echo [-neE] [arg ]
Output the ARGs. If -n is specified, the trailing newline is
suppressed. If the -e option is given, interpretation of the
following backslash-escaped characters is turned on:
a alert (bell)
b backspace
c suppress trailing newline
f form feed
n new line
r carriage return
t horizontal tab
v vertical tab
backslash
num the character whose ASCII code is NUM (octal).

You can explicitly turn off the interpretation of the above characters
with the -E option.

enable

enable: enable [-n] [name ]
Enable and disable builtin shell commands. This allows
you to use a disk command which has the same name as a shell
builtin. If -n is used, the NAMEs become disabled. Otherwise
NAMEs are enabled. For example, to use the `test' found on your
path instead of the shell builtin version, you type `enable -n test'.

eval

eval: eval [arg ]
Read ARGs as input to the shell and execute the resulting command(s).

exec

exec: exec [ [-] file [redirection ]]
Exec FILE, replacing this shell with the specified program.
If FILE is not specified, the redirections take effect in this
shell. If the first argument is `-', then place a dash in the
zeroth arg passed to FILE. If the file cannot be exec'ed and
the shell is not interactive, then the shell exits, unless the
shell variable 'no_exit_on_failed_exec' exists.

exit

exit: exit [n]
Exit the shell with a status of N. If N is omitted, the exit status
is that of the last command executed.

export

export: export [-n] [-f] [name ] or export -p
NAMEs are marked for automatic export to the environment of
subsequently executed commands. If the -f option is given,
the NAMEs refer to functions. If no NAMEs are given, or if `-p'
is given, a list of all names that are exported in this shell is
printed. An argument of `-n' says to remove the export property
from subsequent NAMEs. An argument of `--' disables further option
processing.

fc

fc: fc [-e ename] [-nlr] [first] [last] or fc -s [pat=rep] [cmd]
FIRST and LAST can be numbers specifying the range, or FIRST can be a
string, which means the most recent command beginning with that
string.

-e ENAME selects which editor to use. Default is FCEDIT, then EDITOR,
then the editor which corresponds to the current readline editing
mode, then vi.

-l means list lines instead of editing.
-n means no line numbers listed.
-r means reverse the order of the lines (making it newest listed first).

With the `fc -s [pat=rep ] [command]' format, the command is
re-executed after the substitution OLD=NEW is performed.

A useful alias to use with this is r='fc -s', so that typing `r cc'
runs the last command beginning with `cc' and typing `r' re-executes
the last command.

fg

fg: fg [job_spec]
Place JOB_SPEC in the foreground, and make it the current job. If
JOB_SPEC is not present, the shell's notion of the current job is
used.

for

for: for NAME [in WORDS ;] do COMMANDS; done
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.

function

function: function NAME or NAME ()
Create a simple command invoked by NAME which runs COMMANDS.
Arguments on the command line along with NAME are passed to the
function as $0 .. $n.

getopts

getopts: getopts optstring name [arg]
Getopts is used by shell procedures to parse positional parameters.

OPTSTRING contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an argument,
which should be separated from it by white space.

Each time it is invoked, getopts will place the next option in the
shell variable $name, initializing name if it does not exist, and
the index of the next argument to be processed into the shell
variable OPTIND. OPTIND is initialized to 1 each time the shell or
a shell script is invoked. When an option requires an argument,
getopts places that argument into the shell variable OPTARG.

getopts reports errors in one of two ways. If the first character
of OPTSTRING is a colon, getopts uses silent error reporting. In
this mode, no error messages are printed. If an illegal option is
seen, getopts places the option character found into OPTARG. If a
required argument is not found, getopts places a ':' into NAME and
sets OPTARG to the option character found. If getopts is not in
silent mode, and an illegal option is seen, getopts places '?' into
NAME and unsets OPTARG. If a required option is not found, a '?'
is placed in NAME, OPTARG is unset, and a diagnostic message is
printed.

If the shell variable OPTERR has the value 0, getopts disables the
printing of error messages, even if the first character of
OPTSTRING is not a colon. OPTERR has the value 1 by default.

Getopts normally parses the positional parameters ($0 - $9), but if
more arguments are given, they are parsed instead.

hash

hash: hash [-r] [name ]
For each NAME, the full pathname of the command is determined and
remembered. The -r option causes the shell to forget all remembered
locations. If no arguments are given, information about remembered
commands is presented.

help

help: help [pattern ]
Display helpful information about builtin commands. If PATTERN is
specified, gives detailed help on all commands matching PATTERN,
otherwise a list of the builtins is printed.

history

history: history [n] [ [-awrn] [filename]]
Display the history list with line numbers. Lines listed with
with a `*' have been modified. Argument of N says to list only
the last N lines. Argument `-w' means to write out the current
history file; `-r' means to read it instead. Argument `-a' means
to append history lines from this session to the history file.
Argument `-n' means to read all history lines not already read
from the history file. If FILENAME is given, then use that file,
else if $HISTFILE has a value, use that, else use ~/.bash_history.

if

if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ] [ else COMMANDS; ] fi
The if COMMANDS are executed. If the exit status is zero, then the then
COMMANDS are executed. Otherwise, each of the elif COMMANDS are executed
in turn, and if the exit status is zero, the corresponding then COMMANDS
are executed and the if command completes. Otherwise, the else COMMANDS
are executed, if present. The exit status is the exit status of the last
command executed, or zero if no condition tested true.

jobs

jobs: jobs [-lnp] [jobspec ] | jobs -x command [args]
Lists the active jobs. The -l option lists process id's in addition
to the normal information; the -p option lists process id's only.
If -n is given, only processes that have changed status since the last
notification are printed. JOBSPEC restricts output to that job.
If -x is given, COMMAND is run after all job specifications that appear
in ARGS have been replaced with the process ID of that job's process group
leader.

kill

kill: kill [-s sigspec | -sigspec] [pid | job] | -l [signum]
Send the processes named by PID (or JOB) the signal SIGSPEC. If
SIGSPEC is not present, then SIGTERM is assumed. An argument of `-l'
lists the signal names; if arguments follow `-l' they are assumed to
be signal numbers for which names should be listed. Kill is a shell
builtin for two reasons: it allows job IDs to be used instead of
process IDs, and, if you have reached the limit on processes that
you can create, you don't have to start a process to kill another one.

let

let: let arg [arg ]
Each ARG is an arithmetic expression to be evaluated. Evaluation
is done in long integers with no check for overflow, though division
by 0 is trapped and flagged as an error. The following list of
operators is grouped into levels of equal-precedence operators.
The levels are listed in order of decreasing precedence.

- unary minus
! logical NOT
* / % multiplication, division, remainder
+ - addition, subtraction
<= >= < > comparison
== != equality inequality
= assignment

Shell variables are allowed as operands. The name of the variable
is replaced by its value (coerced to a long integer) within
an expression. The variable need not have its integer attribute
turned on to be used in an expression.

Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.

If the last ARG evaluates to 0, let returns 1; 0 is returned
otherwise.

local

local: local name[=value]
Create a local variable called NAME, and give it VALUE. LOCAL
can only be used within a function; it makes the variable NAME
have a visible scope restricted to that function and its children.

logout

logout: logout
Logout of a login shell.

popd

popd: popd [+n | -n]
Removes entries from the directory stack. With no arguments,
removes the top directory from the stack, and cd's to the new
top directory.

+n removes the Nth entry counting from the left of the list
shown by `dirs', starting with zero. For example: `popd +0'
removes the first directory, `popd +1' the second.

-n removes the Nth entry counting from the right of the list
shown by `dirs', starting with zero. For example: `popd -0'
removes the last directory, `popd -1' the next to last.

You can see the directory stack with the `dirs' command.

pushd

pushd: pushd [dir | +n | -n]
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory. With no arguments, exchanges the top two directories.

+n Rotates the stack so that the Nth directory (counting
from the left of the list shown by `dirs') is at the top.

-n Rotates the stack so that the Nth directory (counting
from the right) is at the top.

dir adds DIR to the directory stack at the top, making it the
new current working directory.

You can see the directory stack with the `dirs' command.

pwd

pwd: pwd
Print the current working directory.

read

read: read [-r] [name ]
One line is read from the standard input, and 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. Only the characters
found in $IFS are recognized as word delimiters. The return code is
zero, unless end-of-file is encountered. If the -r option is given,
this signifies `raw' input, and backslash processing is disabled.

readonly

readonly: readonly [-n] [-f] [name ] or readonly -p
The given NAMEs are marked readonly and the values of these NAMEs may
not be changed by subsequent assignment. If the -f option is given,
then functions corresponding to the NAMEs are so marked. If no
arguments are given, or if `-p' is given, a list of all readonly names
is printed. An argument of `-n' says to remove the readonly property
from subsequent NAMEs. An argument of `--' disables further option
processing.

return

return: 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.

select

select: select NAME [in WORDS ;] do COMMANDS; done
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 or return command is executed.

set

set: set [--abefhknotuvxldHCP] [-o option] [arg ]
-a Mark variables which are modified or created for export.
-b Notify of job termination immediately.
-e Exit immediately if a command exits with a non-zero status.
-f Disable file name generation (globbing).
-h Locate and remember function commands as functions are
defined. Function commands are normally looked up when
the function is executed.
-i Force the shell to be an 'interactive' one. Interactive shells
always read `~/.bashrc' on startup.
-k All keyword arguments are placed in the environment for a
command, not just those that precede the command name.
-m Job control is enabled.
-n Read commands but do not execute them.
-o option-name
Set the variable corresponding to option-name:
allexport same as -a
braceexpand the shell will perform brace expansion
emacs use an emacs-style line editing interface
errexit same as -e
histexpand same as -H
ignoreeof the shell will not exit upon reading EOF
interactive-comments
allow comments to appear in interactive commands
monitor same as -m
noclobber disallow redirection to existing files
noexec same as -n
noglob same as -f
nohash same as -d
notify save as -b
nounset same as -u
physical same as -P
posix change the behavior of bash where the default
operation differs from the 1003.2 standard to
match the standard
privileged same as -p
verbose same as -v
vi use a vi-style line editing interface
xtrace same as -x
-p Turned on whenever the real and effective user ids do not match.
Disables processing of the $ENV file and importing of shell
functions. Turning this option off causes the effective uid and
gid to be set to the real uid and gid.
-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.
-l Save and restore the binding of the NAME in a FOR command.
-d Disable the hashing of commands that are looked up for execution.
Normally, commands are remembered in a hash table, and once
found, do not have to be looked up again.
-H Enable ! style history substitution. This flag is on
by default.
-C If set, disallow existing regular files to be overwritten
by redirection of output.
-P If set, do not follow symbolic links when executing commands
such as cd which change the current directory.

Using + rather than - causes these flags to be turned off. The
flags can also be used upon invocation of the shell. The current
set of flags may be found in $-. The remaining n ARGs are positional
parameters and are assigned, in order, to $1, $2, .. $n. If no
ARGs are given, all shell variables are printed.

shift

shift: shift [n]
The positional parameters from $N+1 are renamed to $1 If N is
not given, it is assumed to be 1.

source

source: source filename
Read and execute commands from FILENAME and return. The pathnames
in $PATH are used to find the directory containing FILENAME.

suspend

suspend: suspend [-f]
Suspend the execution of this shell until it receives a SIGCONT
signal. The `-f' if specified says not to complain about this
being a login shell if it is; just suspend anyway.

test

test: test [expr]
Exits with a status of 0 (trueness) or 1 (falseness) 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 as well, and numeric comparison operators.

File operators:

-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. Use '-L'.
-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 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.

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

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
or STRING True if string is not empty.

STRING1 = STRING2
True if the strings are equal.
STRING1 != STRING2
True if the strings are not equal.

Other operators:

! 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.

times

times: times
Print the accumulated user and system times for processes run from
the shell.

trap

trap: trap [arg] [signal_spec]
The command ARG is to be read and executed when the shell receives
signal(s) SIGNAL_SPEC. If ARG is absent all specified signals 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
SIGNAL_SPEC is EXIT (0) the command ARG is executed on exit from
the shell. The trap command with no arguments prints the list of
commands associated with each signal number. SIGNAL_SPEC is either
a signal name in , or a signal number. The syntax `trap -l'
prints a list of signal names and their corresponding numbers.
Note that a signal can be sent to the shell with 'kill -signal $$'.

type

type: type [-all] [-type | -path] [name ]
For each NAME, indicate how it would be interpreted if used as a
command name.

If the -type flag is used, returns a single word which is one of
`alias', `keyword', `function', `builtin', `file' or `', if NAME is an
alias, shell reserved word, shell function, shell builtin, disk file,
or unfound, respectively.

If the -path flag is used, either returns the name of the disk file
that would be exec'ed, or nothing if -type wouldn't return `file'.

If the -all flag is used, displays all of the places that contain an
executable named `file'. This includes aliases and functions, if and
only if the -path flag is not also used.

typeset

typeset: typeset [-[frxi]] name[=value]
Obsolete. See `declare'.

ulimit

ulimit: ulimit [-SHacdfmstpnuv [limit]]
Ulimit provides control over the resources available to processes
started by the shell, on systems that allow such control. If an
option is given, it is interpreted as follows:

-S use the `soft' resource limit
-H use the `hard' resource limit
-a all current limits are reported
-c the maximum size of core files created
-d the maximum size of a process's data segment
-m the maximum resident set size
-s the maximum stack size
-t the maximum amount of cpu time in seconds
-f the maximum size of files created by the shell
-p the pipe buffer size
-n the maximum number of open file descriptors
-u the maximum number of user processes
-v the size of virtual memory

If LIMIT is given, it is the new value of the specified resource.
Otherwise, the current value of the specified resource is printed.
If no option is given, then -f is assumed. Values are in 1k
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.

umask

umask: umask [-S] [mode]
The user file-creation mask is set to MODE. If MODE is omitted, or if
`-S' is supplied, the current value of the mask is printed. The `-S'
option makes the output symbolic; otherwise an octal number is output.
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).

unalias

unalias: unalias [-a] [name ]
Remove NAMEs from the list of defined aliases. If the -a option is given,
then remove all alias definitions.

unset

unset: unset [-f] [-v] [name ]
For each NAME, remove the corresponding variable or function. Given
the `-v', unset will only act on variables. Given the `-f' flag,
unset will only act on functions. With neither flag, unset first
tries to unset a variable, and if that fails, then tries to unset a
function. Some variables (such as PATH and IFS) cannot be unset; also
see readonly.

until

until: until COMMANDS; do COMMANDS; done
Expand and execute COMMANDS as long as the final command in the
`until' COMMANDS has an exit status which is not zero.

variables

variables: variables - Some variable names and meanings
BASH_VERSION The version numbers of this Bash.
CDPATH A colon separated list of directories to search
when the argument to `cd' is not found in the current
directory.
HISTFILE The name of the file where your command history is stored.
HISTFILESIZE The maximum number of lines this file can contain.
HISTSIZE The maximum number of history lines that a running
shell can access.
HOME The complete pathname to your login directory.
HOSTTYPE The type of CPU this version of Bash is running under.
IGNOREEOF Controls the action of the shell on receipt of an EOF
character as the sole input. If set, then the value
of it is the number of EOF characters that can be seen
in a row on an empty line before the shell will exit
(default 10). When unset, EOF signifies the end of input.
MAILCHECK How often, in seconds, Bash checks for new mail.
MAILPATH A colon-separated list of filenames which Bash checks
for new mail.
PATH A colon-separated list of directories to search when
looking for commands.
PROMPT_COMMAND A command to be executed before the printing of each
primary prompt.
PS1 The primary prompt string.
PS2 The secondary prompt string.
TERM The name of the current terminal type.
auto_resume Non-null means a command word appearing on a line by
itself is first looked for in the list of currently
stopped jobs. If found there, that job is foregrounded.
A value of `exact' means that the command word must
exactly match a command in the list of stopped jobs. A
value of `substring' means that the command word must
match a substring of the job. Any other value means that
the command must be a prefix of a stopped job.
command_oriented_history
Non-null means to save multiple-line commands together on
a single history line.
histchars Characters controlling history expansion and quick
substitution. The first character is the history
substitution character, usually `!'. The second is
the `quick substitution' character, usually `^'. The
third is the `history comment' character, usually `#'.
HISTCONTROL Set to a value of `ignorespace', it means don't enter
lines which begin with a space or tab on the history
list. Set to a value of `ignoredups', it means don't
enter lines which match the last entered line. Set to
`ignoreboth' means to combine the two options. Unset,
or set to any other value than those above means to save
all lines on the history list.

while

while: while COMMANDS; do COMMANDS; done
Expand and execute COMMANDS as long as the final command in the
`while' COMMANDS has an exit status of zero.