Quoting in bash

Separators	; & ( ) | ^ < > new-line space tab
Single quotes	Within single quotes all characters are quoted, including the backslash. The result is one word
Double quotes	Variables are substituted but there is no file name expansion (* and ? are quoted). The result is one word.
Back Quotes	Variables are substituted and there is file name expansion (* and ? are expanded). The result is one word resulting from the execution of the command(s) within quotes.

Concepts and command syntax

Lists
COMMAND && COMMAND2	COMMAND2 is executed iif COMMAND returns an exit status of zero
COMMAND || COMMAND2	COMMAND2 is executed iif COMMAND returns a non-zero exit status
Looping constructs
For the looping constructs, note the following: The symbol ; can always be replaced by one or more newlines The command break leaves the enclosing loop (can be followed by a number N, to leave the Nth enclosing loop) The command continue resumes the execution of the enclosing loop (can be followed by a number N, to resume the Nth enclosing loop)
until TEST-COMMANDS do CONSEQUENT-COMMANDS done	Execute CONSEQUENT-COMMANDS as long as the final command in TEST-COMMANDS has an exit status which is not zero
while TEST-COMMANDS do CONSEQUENT-COMMANDS done	Execute CONSEQUENT-COMMANDS as long as the final command in TEST-COMMANDS has an exit status of zero
for NAME [in WORDS ...] do COMMANDS done	Execute COMMANDS for each member in WORDS, with NAME bound to the current member. If `in WORDS' is not present, `in "$@"' is assumed
Conditional constructs
if TEST-COMMANDS then   CONSEQUENT-COMMANDS [elif MORE-TEST-COMMANDS then   MORE-CONSEQUENTS] [else   ALTERNATE-CONSEQUENTS;] fi	Execute CONSEQUENT-COMMANDS only if the final command in TEST-COMMANDS has an exit status of zero. Otherwise, each `elif' list is executed in turn, and if its exit status is zero, the corresponding MORE-CONSEQUENTS is executed and the command completes. If `else ALTERNATE-CONSEQUENTS' is present, and the final command in the final `if' or `elif' clause has a non-zero exit status, then execute ALTERNATE-CONSEQUENTS
case WORD in [ ( PATTERN [| PATTERN]...) COMMANDS ;;] ... esac	Selectively execute COMMANDS based upon WORD matching PATTERN. The `|' is used to separate multiple patterns. See also example
select NAME [in WORDS ...] do COMMANDS done	The list of words following `in' is expanded, generating a list of items. The set of expanded words is printed on the standard error, each preceded by a number. If the `in WORDS' is omitted, the positional parameters are printed. The `PS3' prompt is then displayed and a line is read from the standard input. If the line consists of a number corresponding to one of the displayed words, then the value of NAME is set to that word. If the line is empty, the words and prompt are displayed again. If `EOF' is read, the `select' command completes. Any other value read causes NAME to be set to null. The line read is saved in the variable `REPLY'
Functions
[ `function' ] NAME () { COMMAND-LIST; }	This defines a shell function named NAME. The reserved word `function' is optional. The BODY of the function is the COMMAND-LIST between { and }. This list is executed whenever NAME is specified as the name of a command. The exit status of a function is the exit status of the last command executed in the body. When a function is executed, the arguments to the function become the positional parameters during its execution. The special parameter `#' that expands to the number of positional parameters is updated to reflect the change. Positional parameter `0' is unchanged. If the builtin command `return' is executed in a function, the function completes and execution resumes with the next command after the function call. When a function completes, the values of the positional parameters and the special parameter `#' are restored to the values they had prior to function execution. If a numeric argument is given to `return', that is the function return status.

Shell expansions

Brace expansion
example	result	Notes
echo a{b,c,d}e	abe ace ade	This is a simple textual expansion. The comma separated values within the braces replace the braces, for each value

Variable substitutions

pattern matching
example foo="this is a test"	result	notes
echo ${foo#t*is}	is a test	Deletes the shortest match from the left
echo ${foo##t*is}	a test	Deletes the longest match from the left
echo ${foo%t*st}	this is a	Deletes the shortest match from the right
echo ${foo%%t*st}		Deletes the longest match from the right (result is empty in the example)
Substitution
example	result	notes
export foo="" echo ${foo:-one}	one	Default evaluation: if the variable exists and is not null, it is returned, otherwise the given value is returned. The variable is not changed.
export foo="" echo ${foo:=one}	one	Default attribution: if the variable exists and is not null, it is returned, otherwise the given value is attributed to the variable and the result returned. The variable is changed.
export foo="this is a test" echo ${foo:+one}	one	Constant or null evaluation: if the variable exists and is not null, the given value is returned, otherwise null is returned. The variable is not changed.
export foo="" echo ${foo:?"Error message"}	Error message	Test for existence: if the variable exists and is not null, it is returned, otherwise the given error message is printed. The variable is not changed.
String operations
example foo="patagonia"	result	notes
echo ${#foo}	9	Returns the length of the variable
echo ${foo:4}	gonia	Returns the part of the string starting at a given offset, the first character being the 0th character
echo ${foo:4:2}	go	Returns the part of the string starting at a given offset, the first character being the 0th character, with a maximum of characters also given
echo ${foo/pata/be}	begonia	Returns the replacement of the first match by the replacement string. If the pattern string begins with # will match only at the start; if the pattern string begins with % will match only at the end.
echo ${foo//a/o}	potogonio	Returns the replacement of the all matches by the replacement string. If the pattern string begins with # will match only at the start; if the pattern string begins with % will match only at the end.

bash builtins

bash builtins index
: . source alias bg bind break builtin cd command continue declare typeset dirs disown echo enable eval exec exit export fc fg getopts hash help history jobs kill let local logout popd pushd pwd read readonly return set shift shopt suspend test [] times trap type ulimit umask unalias unset wait
bash builtins
: [arguments]	index
No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned.
. filename [arguments] source filename [arguments]	index
Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, file names in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. The current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found.
alias [-p] [name[=value] ...]	index
Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, 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 when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined.
bg [jobspec]	index
Place jobspec in the background, as if it had been started with &. If jobspec is not present, the shell's notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job control enabled, if jobspec was not found or started without job control.
bind [-m keymap] [-lpsvPSV] [-q name] [-r keyseq] bind [-m keymap] -f filename bind [-m keymap] keyseq:function-name	index
Display current readline key and function bindings, or bind a key sequence to a readline function or macro. The binding syntax accepted is identical to that of .inputrc, but each binding must be passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options, if supplied, have the following meanings: -m keymap Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command , and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. -l List the names of all readline functions. -p Display readline function names and bindings in such a way that they can be re-read. -P List current readline function names and bindings. -v Display readline variable names and values in such a way that they can be re-read. -V List current readline variable names and values. -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read. -S Display readline key sequences bound to macros and the strings they output. -f filename Read key bindings from filename. -q function Query about which keys invoke the named function. -r keyseq Remove any current binding for keyseq. The return value is 0 unless an unrecognized option is given or an error occurred.
break [n]	index
Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be >= 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not executing a loop when break is executed.
builtin shell-builtin [arguments]	index
Execute the specified shell builtin, passing it arguments, and return its exit status. This is useful when you wish to define a function whose name is the same as a shell builtin, but need the functionality of the builtin within the function itself. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command.
cd [-LP] [dir]	index
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 in CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ``.''. If dir begins with a slash (/), then CDPATH is not used. The -P option says to use the physical directory structure instead of following symbolic links (see also the -P option to the set builtin command); the -L option forces symbolic links to be followed. An argument of - is equivalent to $OLDPWD. The return value is true if the directory was successfully changed; false otherwise.
command [-pVv] command [arg ...]	index
Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or file name used to invoke command to be printed; the -V option produces a more verbose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command.
continue [n]	index
Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be >= 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless the shell is not executing a loop when continue is executed.
declare [-afFirx] [-p] [name[=value]] typeset [-afFirx] [-p] [name[=value]]	index
Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used, additional options are ignored. The -F option inhibits the display of function definitions; only the function name and attributes are printed. The -F option implies -f. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes: -a Each name is an array variable. -f Use function names only. -i The variable is treated as an integer; arithmetic evaluation is performed when the variable is assigned a value. -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements. -x Mark names for export to subsequent commands via the environment. Using + instead of - turns off the attribute instead, with the exception that +a may not be used to destroy an array variable. When used in a function, makes each name local, as with the local command. The return value is 0 unless ... an illegal option is encountered an attempt is made to define a function using "-f foo=bar" an attempt is made to assign a value to a readonly variable an attempt is made to assign a value to an array variable without using the compound assignment syntax one of the names is not a legal shell variable name an attempt is made to turn off readonly status for a readonly variable an attempt is made to turn off array status for an array variable or an attempt is made to display a non-existent function with -f
dirs [-clpv] [+n] [-n]	index
Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes entries from the list. +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. -c Clears the directory stack by deleting all of the entries. -l Produces a longer listing; the default listing format uses a tilde to denote the home directory. -p Print the directory stack with one entry per line. -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack. The return value is 0 unless an illegal option is supplied or n indexes beyond the end of the directory stack.
disown [-h] [jobspec ...]	index
Without options, each jobspec is removed from the table of active jobs. If the -h option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is present, the current job is used. The return value is 0 unless a jobspec does not specify a valid job.
echo [-neE] [arg ...]	index
Output the args, separated by spaces, followed by a newline. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default. echo does not interpret -- to mean the end of options. echo interprets the following escape sequences: \a alert (bell) \b backspace \c suppress trailing newline \e an escape character \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash \nnn the character whose ASCII code is nnn (octal)
enable [-adnps] [-f filename] [name ...]	index
Enable and disable builtin shell commands. This allows the execution of a disk command which has the same name as a shell builtin without specifying a full file name. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, run enable -n test. The -f option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name arguments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is a problem loading a new builtin from a shared object.
eval [arg ...]	index
The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0.
exec [-cl] [-a name] [command] [arguments]	index
If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell places a dash in the zeroth arg passed to command. This is what login(1) does. The -c option causes command to be executed with an empty environment. If -a is supplied, the shell passes name as the zeroth argument to the executed command. If command cannot be executed for some reason, a non-interactive shell exits, unless the shell option execfail is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If command is not specified, any redirections take effect in the current shell, and the return status is 0.
exit [n]	index
Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell terminates.
export [-fn] [name[=word]] ... export -p	index
The supplied 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 the -p option is supplied, a list of all names that are exported in this shell is printed. The -n option causes the export property to be removed from the named variables. export returns an exit status of 0 unless an illegal option is encountered, one of the names is not a legal shell variable name, or -f is supplied with a name that is not a function.
fc [-e ename] [-nlr] [first] [last] fc -s [pat=rep] [cmd]	index
Fix Command. In the first form, a range of commands from first to last is selected from the history list. First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to the current command for listing (so that fc -l -10 prints the last 10 commands) and to first otherwise. If first is not specified it is set to the previous command for editing and -16 for listing. The -n flag suppresses the command numbers when listing. The -r flag reverses the order of the commands. If the -l flag is given, the commands are listed on standard output. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, is used. When editing is complete, the edited commands are echoed and executed. In the second form, command is re-executed after each instance of pat is replaced by rep. 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. If the first form is used, the return value is 0 unless an illegal option is encountered or first or last specify history lines out of range. If the -e option is supplied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure.
fg [jobspec]	index
Place jobspec in the foreground, and make it the current job. If jobspec is not present, the shell's notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control.
getopts optstring name [args]	index
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 places 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 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 variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when illegal options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error message will be displayed, even if the first character of optstring is not a colon. If an illegal option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the option character found. getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs.
hash [-r] [-p filename] [name]	index
For each name, the full file name of the command is determined by searching the directories in $PATH and remembered. If the -p option is supplied, no path search is performed, and filename is used as the full file name of the command. The -r option causes the shell to forget all remembered locations. If no arguments are given, information about remembered commands is printed. The return status is true unless a name is not found or an illegal option is supplied.
help [pattern]	index
Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the builtins and shell control structures is printed. The return status is 0 unless no command matches pattern.
history [-c] [n] history -anrw [filename] history -p arg [arg ...] history -s arg [arg ...]	index
With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings: -a Append the ``new'' history lines (history lines entered since the beginning of the current bash session) to the history file. -n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session. -r Read the contents of the history file and use them as the current history. -w Write the current history to the history file, overwriting the history file's contents. -c Clear the history list by deleting all the entries. -p Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must be quoted to disable normal history expansion. -s Store the args in the history list as a single entry. The last command in the history list is removed before the args are added. The return value is 0 unless an illegal option is encountered or an error occurs while reading or writing the history file.
jobs [-lnprs] [ jobspec ... ] jobs -x command [ args ... ]	index
The first form lists the active jobs. The options have the following meanings: -l List process IDs in addition to the normal information. -p List only the process ID of the job's process group leader. -n Display information only about jobs that have changed status since the user was last notified of their status. -r Restrict output to running jobs. -s Restrict output to stopped jobs. If jobspec is given, output is restricted to information about that job. The return status is 0 unless an illegal option is encountered or an illegal jobspec is supplied. If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and executes command passing it args, returning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ... kill -l [signum | sigspec]	index
Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a signal name such as SIGKILL or a signal number; signum is a signal number. If sigspec is a signal name, the name may be given with or without the SIG prefix. If sigspec is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are supplied when -l is given, the names of the specified signals are listed, and the return status is 0. The arguments to -l may be either signal names or signal numbers; if signal names are given, the corresponding signal number is displayed. kill returns true if at least one signal was successfully sent, or false if an error occurs or an illegal option is encountered.
let arg [arg ...]	index
Each arg is an arithmetic expression to be evaluated. If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.
local [name[=value] ...]	index
For each argument, create a local variable named name, and assign it value. When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children. With no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, or an illegal name is supplied.
logout	index
Exit a login shell.
popd [-n] [+n] [-n]	index
Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd to the new top directory. Arguments, if supplied, have the following meanings: +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. -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an illegal option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails.
pushd [-n] [dir] pushd [-n] [+n] [-n]	index
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 and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings: +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top. -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top. -n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. dir Adds dir to the directory stack at the top, making it the new current working directory. If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails.
pwd [-LP]	index
Print the absolute file name of the current working directory. The file name printed contains no symbolic links if the -P option is supplied or the -o physical option to the set builtin command is enabled. If the -L option is used, symbolic links are followed. The return status is 0 unless an error occurs while reading the name of the current directory.
read [-er] [-a aname] [-p prompt] [name ...]	index
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, and so on, with leftover words assigned to the last name. Only the characters in IFS are recognized as word delimiters. Options, if supplied, have the following meanings: -r A backslash-newline pair is not ignored, and the backslash is considered to be part of the line. -p Display prompt, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. -a The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. -e If the standard input is coming from a terminal, readline is used to obtain the line. If no names are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered.
readonly [-apf] [name ...]	index
The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to the names are so marked. The -a option restricts the variables to arrays. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The return status is 0 unless an illegal option is encountered, one of the names is not a legal shell variable name, or -f is supplied with a name that is not a function.
return [n]	index
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 in the function body. If used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script. If used outside a function and not during execution of a script by ., the return status is false.
set [--abefhkmnptuvxBCHP] [-o option] [arg ...]	index
Without options, the name and value of each shell variable are displayed in a format that can be reused as input. When options are specified, they set or unset shell attributes. Any arguments remaining after the options are processed are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings: -a Automatically mark variables which are modified or created for export to the environment of subsequent commands. -b Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled. -e Exit immediately if a simple command exits with a non-zero status. The shell does not exit if the command that fails is part of an until or while loop, part of an if statement, part of a && or || list, or if the command's return value is being inverted via !. -f Disable pathname expansion. -h Remember the location of commands as they are looked up for execution. This is on by default. -k All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name. -m Monitor mode. Job control is enabled. This flag is on by default for interactive shells on systems that support it. Background processes run in a separate process group and a line containing their exit status is printed upon their completion. -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells. -o option-name The option-name can be one of the following: allexport Same as -a. braceexpand Same as -B. emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the --noediting option. errexit Same as -e. hashall Same as -h. histexpand Same as -H. history Enable command history, as described above under HISTORY. This option is on by default in interactive shells. ignoreeof The effect is as if the shell command IGNOREEOF=10 had been executed. keyword Same as -k. monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. notify Same as -b. nounset Same as -u. onecmd Same as -t. physical Same as -P. posix Change the behavior of bash where the default operation differs from the POSIX 1003.2 standard to match the standard. privileged Same as -p. verbose Same as -v. vi Use a vi-style command line editing interface. xtrace Same as -x. If -o is supplied with no option-name, the values of the current options are printed. If +o is supplied with no option-name, a series of set commands to recreate the current option settings is displayed on the standard output. -p Turn on privileged mode. In this mode, the $ENV file is not processed, and shell functions are not inherited from the environment. This is enabled automatically on startup if the effective user (group) id is not equal to the real user (group) id. Turning this option off causes the effective user and group ids to be set to the real user and group ids. -t Exit after reading and executing one command. -u Treat unset variables as an error when performing parameter expansion. If expansion is attempted on an unset variable, the shell prints an error message, and, if not interactive, exits with a non-zero status. -v Print shell input lines as they are read. -x After expanding each simple command, display the expanded value of PS4, followed by the command and its expanded arguments. -B The shell performs brace expansion. This is on by default. -C If set, bash does not overwrite an existing file with the >, >&, and <> redirection operators. This may be overridden when creating output files by using the redirection operator >| instead of >. -H Enable ! style history substitution. This flag is on by default when the shell is interactive. -P If set, the shell does not follow symbolic links when executing commands such as cd that change the current working directory. It uses the physical directory structure instead. By default, bash follows the logical chain of directories when performing commands which change the current directory. -- If no arguments follow this flag, then the positional parameters are unset. Otherwise, the positional parameters are set to the args, even if some of them begin with a -. - Signal the end of options, cause all remaining args to be assigned to the positional parameters. The -x and -v options are turned off. If there are no args, the positional parameters remain unchanged. The flags are off by default unless otherwise noted. Using + rather than - causes these flags to be turned off. The flags can also be specified as options to an invocation of the shell. The current set of flags may be found in $-. The return status is always true unless an illegal option is encountered.
shift [n]	index
The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n is greater than $#, the positional parameters are not changed. The return status is greater than zero if n is greater than $# or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]	index
Toggle the values of variables controlling optional shell behavior. With no options, or with the -p option, a list of all setable options is displayed, with an indication of whether or not each is set. Other options have the following meanings: -s Enable (set) each optname. -u Disable (unset) each optname. -q Suppresses normal output (quiet mode); the return status indicates whether the optname is set or unset. If multiple optname arguments are given with -q, the return status is zero if all optnames are enabled; nonzero otherwise. -o Restricts the values of optname to be those defined for the -o option to the set builtin. If either -s or -u is used with no optname arguments, the display is limited to those options which are set or unset, respectively. Unless otherwise noted, the shopt options are disabled (unset) by default. The return status when listing options is zero if all optnames are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an optname is not a legal shell option. The list of shopt options is: cdable_vars If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to. cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected file name is printed, and the command proceeds. This option is only used by interactive shells. checkhash If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed. checkwinsize If set, bash checks the window size after each command and, if necessary, updates the values of LINES and COLUMNS. cmdhist If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands. dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expansion. execfail If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin command. An interactive shell does not exit if exec fails. expand_aliases If set, aliases are expanded as described above under ALIASES. This option is enabled by default for interactive shells. histappend If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file. histreedit If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution. histverify If set, and readline is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the readline editing buffer, allowing further modification. hostcomplete If set, and readline is being used, bash will attempt to perform hostname completion when a word beginning with @ is being completed. This is enabled by default. interactive_comments If set, allow a word beginning with # to cause that word and all remaining characters on that line to be ignored in an interactive shell. This option is enabled by default. lithist If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible. mailwarn If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the message ``The mail in mailfile has been read'' is displayed. nullglob If set, bash allows patterns which match no files to expand to a null string, rather than themselves. promptvars If set, prompt strings undergo variable and parameter expansion after being expanded as described in PROMPTING above. This option is enabled by default. shift_verbose If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters. sourcepath If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an argument. This is enabled by default.
suspend [-f]	index
Suspend the execution of this shell until it receives a SIGCONT signal. The -f option says not to complain if this is a login shell; just suspend anyway. The return status is 0 unless the shell is a login shell and -f is not supplied, or if job control is not enabled.
test expr [ expr ]	index
Return a status of 0 or 1 depending on the evaluation of the conditional expression 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. Each operator and operand must be a separate argument. If file is of the form /dev/fd/n, then file descriptor n is checked. Expressions are composed of the following primaries (see also test page): -b file True if file exists and is a block special file. -c file True if file exists and is a character special file. -d file True if file exists and 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 exists and is set-group-id. -k file True if file has its ``sticky'' bit set. -L file True if file exists and is a symbolic link. -p file True if file exists and is a named pipe. -r file True if file exists and is readable. -s file True if file exists and has a size greater than zero. -S file True if file exists and is a socket. -t fd True if fd is opened on a terminal. -u file True if file exists and its set-user-id bit is set. -w file True if file exists and is writable. -x file True if file exists and is executable. -O file True if file exists and is owned by the effective user id. -G file True if file exists and is owned by the effective group id. file1 -nt file2 True if file1 is newer (according to modification date) than file2. file1 -ot file2 True if file1 is older than file2. file1 -ef file2 True if file1 and file2 have the same device and inode numbers. -o optname True if shell option optname is enabled. See the list of options under the description of the -o option to the set builtin above. -z string True if the length of string is zero. -n string string True if the length of string is non-zero. string1 = string2 True if the strings are equal. == may be used in place of =. 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. ! 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 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers.
times	index
Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0.
trap [-lp] [arg] [sigspec ...]	index
The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent or -, all specified signals are reset to their original values (the values they had upon entrance to the shell). If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes. If arg is -p then the trap commands associated with each sigspec are displayed. If no arguments are supplied or if only -p is given, trap prints the list of commands associated with each signal number. Each sigspec is either a signal name defined in <<u>signal.h>, or a signal number. If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is executed after every simple command. The -l option causes the shell to print a list of signal names and their corresponding numbers. Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child process when it is created. The return status is false if any sigspec is invalid; otherwise trap returns true.
type [-all] [-type | -path] name [name ...]	index
With no options, indicate how each name would be interpreted if used as a command name. If the -ty

Usages

To redirect stderr to stdout:

gzip --help 2>&1 | less

To operate on all files with a * path

for foo in * ; do echo $foo ; done

case..esac example:

echo -n "Enter the name of an animal: "
read ANIMAL
echo -n "The $ANIMAL has "
case $ANIMAL in
  horse | dog | cat) echo -n "four";;
  man | kangaroo ) echo -n "two";;
  *) echo -n "an unknown number of";;
esac
echo " legs."

To rename a file with a odd path, the following can be used (see also Brace expansion):

mv /a/long/common/path/{original_name,new_name}

To see the sizes of all directories in current path:

find . -maxdepth 1 -type d -print | xargs du -sk

How to extract part of a name. See following example, where the first part of files named anything.tar.gz is evaluated to anything

for foo in *.tar.gz
do
  echo "$foo --> ${foo%*.tar.gz}"
done

How to convert all filenames in the current directory to lowercase names. See following script:

#!/bin/sh
export name=""
export namelow=""

ls > dirtmp.txt
cat dirtmp.txt|while read name
do
  namelow=`echo $name|tr A-Z a-z`
  if [ "$name" != "$namelow" ]
  then
    echo "Renaming $name to $namelow"
    mv $name $namelow
  fi
done
rm dirtmp.txt

Keyboard shortcuts

Bash keyboard shortcuts
Keys	result
ESC .	Inserts the last word of the previous command

Externals

The umask command defines the bits that are turned off for a file created by the user. Does not apply to the execute bits. See also File permissions.