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The great GNU Bourne-Again ShellEdit

Bash is the shell, or command language interpreter, that will appear in the GNU Operating System.

Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh).

Bash LinksEdit

Useful Keyboard combinations in BashEdit

With control (crtl)Edit

  • crtl-a = start of line
  • crtl-e = end of line
  • crtl-l = clears the screen, like command clear
  • crtl-p = previous command from history, like page up key
  • crtl-r = reverse search in history(incremental)

With escape(esc)Edit

  • esc-f = one word forward
  • esc-b = one word backward


Assignment OperatorsEdit


All-purpose assignment operator, which works for both arithmetic and string assignments.Do not confuse the "=" assignment operator with the = test operator.

Arithmetic OperatorsEdit












modulo, or mod (returns the remainder of an integer division operation)


"plus-equal" (increment variable by a constant). let "var += 5" results in var being incremented by 5.


"minus-equal" (decrement variable by a constant)


"times-equal" (multiply variable by a constant). let "var *= 4" results in var being multiplied by 4.


"slash-equal" (divide variable by a constant)


"mod-equal" (remainder of dividing variable by a constant)

Logical OperatorsEdit


and (logical). if [ $condition1 ] && [ $condition2 ]


or (logical). if [ $condition1 ] || [ $condition2 ]

Dont confuse those with #Conditional executing.

Comparison OperatorsEdit


is equal to. if [ "$a" -eq "$b" ]


is not equal to. if [ "$a" -ne "$b" ]


is greater than. if [ "$a" -gt "$b" ]


is greater than or equal to if. [ "$a" -ge "$b" ]


is less than. if [ "$a" -lt "$b" ]


is less than or equal to. if [ "$a" -le "$b" ]


is less than. (within double parentheses) (("$a" < "$b"))


is less than or equal to. (within double parentheses). (("$a" <= "$b"))


is greater than (within double parentheses). (("$a" > "$b"))


is greater than or equal to (within double parentheses). (("$a" >= "$b"))


is equal to. if [ "$a" = "$b" ]


is equal to. if [ "$a" == "$b" ]


is not equal to. if [ "$a" != "$b" ]


is less than, in ASCII alphabetical order


is greater than, in ASCII alphabetical order


string is "null", that is, has zero length


string is not "null".

Bitwise OperatorsEdit


bitwise left shift (multiplies by 2 for each shift position)


"left-shift-equal" let "var <<= 2" results in var left-shifted 2 bits (multiplied by 4)


bitwise right shift (divides by 2 for each shift position)


"right-shift-equal" (inverse of <<=)


bitwise and


bitwise and-equal


bitwise OR


bitwise OR-equal


bitwise negate


bitwise NOT


bitwise XOR


bitwise XOR-equal

Misc OperatorsEdit


comma operator . The comma operator chains together two or more arithmetic operations. All the operations are evaluated (with possible side effects), but only the last operation is returned.

Conditional executingEdit

command1 && command2

command2 is executed if, and only if, command1 returns an exit status of zero. (exit status zero means succesful)

command1 || command2

command2 is executed if and only if command1 returns a non-zero exit status. (non-zero exit status means failed)

command1 && command2 || command3 

if command1 is executed successfully then shell will run command2 and if command1 is not successful then command3 is executed.

Wildcards / regexEdit

These can be used on filenames.


zero or more characters


exactly one character


exactly one character listed


exactly one character in the given range


any character that is not listed


any character that is not in the given range


exactly one entire word in the options given

You can use wildcards with any command that accepts file names as arguments.

also see: Bash Scripts


Bash built-in commandsEdit

GNU bash, version 2.05a.0(1)-release (i386-pc-linux-gnu)
These shell commands are defined internally.  Type `help' to see this list.
Type 'help name' to find out more about the function `name'.
Use 'info bash' to find out more about the shell in general.

A star (*) next to a name means that the command is disabled.

 %[DIGITS | WORD] [&]               . filename
 :                                  [ arg... ]
 alias [-p] [name[=value] ... ]     bg [job_spec]
 bind [-lpvsPVS] [-m keymap] [-f fi break [n]
 builtin [shell-builtin [arg ...]]  case WORD in [PATTERN [| PATTERN].
 cd [-PL] [dir]                     command [-pVv] command [arg ...]
 compgen [-abcdefgjkvu] [-o option] complete [-abcdefgjkvu] [-pr] [-o 
 continue [n]                       declare [-afFrxi] [-p] name[=value
 dirs [-clpv] [+N] [-N]             disown [-h] [-ar] [jobspec ...]
 echo [-neE] [arg ...]              enable [-pnds] [-a] [-f filename] 
 eval [arg ...]                     exec [-cl] [-a name] file [redirec
 exit [n]                           export [-nf] [name ...] or export 
 false                              fc [-e ename] [-nlr] [first] [last
 fg [job_spec]                      for NAME [in WORDS ... ;] do COMMA
 function NAME { COMMANDS ; } or NA getopts optstring name [arg]
 hash [-r] [-p pathname] [-t] [name help [-s] [pattern ...]
 history [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [ elif
 jobs [-lnprs] [jobspec ...] or job kill [-s sigspec | -n signum | -si
 let arg [arg ...]                  local name[=value] ...
 logout                             popd [+N | -N] [-n]
 printf format [arguments]          pushd [dir | +N | -N] [-n]
 pwd [-PL]                          read [-ers] [-t timeout] [-p promp
 readonly [-anf] [name ...] or read return [n]
 select NAME [in WORDS ... ;] do CO set [--abefhkmnptuvxBCHP] [-o opti
 shift [n]                          shopt [-pqsu] [-o long-option] opt
 source filename                    suspend [-f]
 test [expr]                        time [-p] PIPELINE
 times                              trap [arg] [signal_spec ...] or tr
 true                               type [-apt] name [name ...]
 typeset [-afFrxi] [-p] name[=value ulimit [-SHacdflmnpstuv] [limit]
 umask [-p] [-S] [mode]             unalias [-a] [name ...]
 unset [-f] [-v] [name ...]         until COMMANDS; do COMMANDS; done
 variables - Some variable names an wait [n]
 while COMMANDS; do COMMANDS; done  { COMMANDS ;

use help <command>, f.e help shift to get more information about the commands.

Bash on Mac OS XEdit

Bash on WindowsEdit