The great GNU Bourne-Again Shell[edit]
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 Links[edit]
Useful Keyboard combinations in Bash[edit]
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
Operators[edit]
Assignment Operators[edit]
=
All-purpose assignment operator, which works for both arithmetic and string assignments.Do not confuse the "=" assignment operator with the = test operator.
Arithmetic Operators[edit]
+
plus
-
minus
*
multiplication
/
division
**
exponentiation
%
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 Operators[edit]
&&
and (logical). if [ $condition1 ] && [ $condition2 ]
||
or (logical). if [ $condition1 ] || [ $condition2 ]
Dont confuse those with #Conditional executing.
Comparison Operators[edit]
Integers[edit]
-eq
is equal to. if [ "$a" -eq "$b" ]
-ne
is not equal to. if [ "$a" -ne "$b" ]
-gt
is greater than. if [ "$a" -gt "$b" ]
-ge
is greater than or equal to if. [ "$a" -ge "$b" ]
-lt
is less than. if [ "$a" -lt "$b" ]
-le
is less than or equal to. if [ "$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" >= "$b"))
Strings[edit]
=
is equal to. if [ "$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
-z
string is "null", that is, has zero length
-n
string is not "null".
Bitwise Operators[edit]
<<
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 Operators[edit]
,
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 executing[edit]
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 / regex[edit]
These can be used on filenames.
*
zero or more characters
?
exactly one character
[abcde]
exactly one character listed
[a-e]
exactly one character in the given range
[!abcde]
any character that is not listed
[!a-e]
any character that is not in the given range
{debian,linux}
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
<man>bash</man>
Bash built-in commands[edit]
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.