Bash

Bash

Bash is a Unix shell and command language written by Brian Fox as a replacement for the Bourne shell

Lingo

C	Ctrl
M	Meta Key (Alt or ESC)

Shortcuts

C-c	Interrupt running process
C-z	Suspend running process
C-d	Exit from current shell
C-l	Clear Screen
C-a	Move at the start of the line
C-e	Move at the end of the line
M-←	Move backward by a word
M-b	Move backward by a word (alternative)
M-→	Move forward by a word
M-f	Move forward by a word (alternative)
C-x, C-x	Move cursor between start of line and current position
M-t	Swap the last two words before the cursor
C-t	Swap the last two characters before the cursor
M-Backspace	Delete a word (backward)
C-w	Delete a word (backward) (alternative)
M-d	Delete a word (forward)
C-h	Delete one character backward (same as Backspace)
C-k	Kill from cursor to the end of line
C-u	Kill from cursor to the beginning of line
M-u	Upper-case from cursor to the end of word
M-l	Lower-case from cursor to the end of word
M-c	Capitalize word (from cursor position)
C-y	Paste
C-_	Undo
M-r	Revert to original command (before editing it)
C-p	Get previous command
C-n	Get next command
C-r, <pattern>	Search previous command containing
M-.	Insert last argument of last command
M-<N>, C-M-y	Get Nth argument of previous command (N=0 gives the command)
M-<	Insert oldest command from history
C-x, C-v	Show bash version
C-x, C-e	Edit current line with ${EDITOR}

Special Variables

!$	Last argument of last command
$<N>	Nth argument of current process (positional parameter)
$#	Number of arguments given to current process
$@	Command line arguments for current process
$*	Without quotes, same as ‘$@’
"$*"	Command line arguments for current process, expanded to a single argument
$0	The name of the shell program
$?	Exit code of previous command
$$	PID of current shell or script
:	Dummy placeholder (produces no output)
!-<N>	Execute Nth command from history
!!	Execute last command
!<string>	Execute last command starting with

Standard File Descriptors

0	stdin
1	stdout
2	stderr

Arithmetic Operators

+	Addition
-	Subtraction
++	Increment
--	Decrement
*	Multiplication
/	Division
%	Modulo
**	Exponentiation
<<	Bit-shift left
>>	Bit-shift right
<	Comparison (less than)
-lt	Comparison (less than) (alternative)
<=	Comparison (less than or equal)
-le	Comparison (less than or equal) (alternative)
>	Comparison (greater than)
-gt	Comparison (greater than) (alternative)
>=	Comparison (greater than or equal)
-ge	Comparison (greater than or equal) (alternative)
==	Comparison (equal)
!=	Comparison (not equal)
&	Bitwise AND
^	Bitwise exclusive OR
\|	Bitwise OR
&&	Logical AND
\|	Logical OR

IO Redirection

cmd > file	Send cmd output to file (overwrite)
cmd >> file	Send cmd output to file (append)
cmd < file	Contents of file are passed to cmd’s stdin
cmd1 \| cmd2	Output of cmd1 is passed to cmd2’s stdin
cmd &> file	Redirect both stdout and stderr to file (overwrite)
cmd &>> file	Redirect both stdout and stderr to file (append)
cmd >&n	Send cmd’s stdout to file descriptor n
cmd m>&n	Same as above except that output that would normally go to file descriptor m, will also go to n
cmd <&n	File descriptor n becomes stdin for cmd
cmd m<&n	Same as above except that stdin that would normally come from file descriptor m, will now come from n
cmd >&-	Close stdout
cmd <&-	Close stdin

Expansion And Other Operators

${var:pos}	Extracts substring from var at pos
${var:pos:len}	Extracts len characters of substring from var at pos
${var:-val}	If $var exists and isn’t NULL, return its value; otherwise return val
${var:=val}	If $var exists and isn’t NULL, return its value; otherwise set it to val and then return its value
${var:?val}	If $var exists and isn’t NULL, return its value; otherwise return ‘var: val’ and abort
${var:?}	If $var exists and isn’t NULL, return its value; otherwise return ‘var: parameter null or not set’ and abort
${var:+val}	If $var exists and isn’t NULL, return val; otherwise return NULL
$((...))	Arithmetic Expansion
${#var}	String length operator
${str#substr}	Deletes shortest match of substr from front of str
${str##substr}	Deletes longest match of substr from front of str
${str%substr}	Deletes shortest match of substr from back of str
${str%%substr}	Deletes longest match of substr from back of str
${str/substr/val}	Replace first match of substr with val
${str//substr/val}	Replace all matches of substr with val
${str/#substr/val}	If $substr matches front end of str, substitute val for substr
${str/%substr/val}	If $substr matches back end of str, substitute val for substr
${str^substr}	Upper-case of first match of substr. An empty pattern selects first char.
${str^^substr}	Upper-case of all matches of substr. An empty pattern selects the whole string.
${str,substr}	Lower-case first match of substr. An empty pattern selects first char.
${str,,substr}	Lower-case all matches of substr. An empty pattern selects the whole string.

Conditionals

if [$hello == "world"] ; then ...; fi	If statement
elif [$hello == "world"] ; then	Else if statement
else	Else statement
fi	End if statement
case "$hello" in	Case statement
a) echo world ;;	Case entry “a”
*) echo default ;;	Default case entry (matches everything)
esac	End case statement

Loops

for ((i = 1; i <= 10; i++)) ; do [expressions] done	For loop running 10 times
for i in $list ; do [expressions] done	For loop being executed for every item in $list
while (i <= 10) ; do [expressions] done	While loop
done	End loop

Exit Statuses

0	Success
!=0	Failure

Auto-Completion

TAB	Auto-complete (hit twice when ambiguous)
~, TAB TAB	Display all users from /etc/passwd
$, TAB TAB	Display all system variables
<string>, M-/	Auto-complete/display files and directories starting with
<string>, M-?	Display commands starting with
M-*	Insert all possible completions

Misc

a=$(cmd)	$a now holds cmd’s output
a=`cmd`	$a now holds cmd’s output (alternative)
cmd &	Execute cmd in the background (fork)

TCP/UDP Sockets

cat < /dev/tcp/<hostname>/<port>	Open a TCP socket to at and write the contents of stdin
cat < /dev/udp/<hostname>/<port>	Open a UDP socket to at and write the contents of stdin