Bash

Some useful terminal commands

Command/Key	Description
grep -i	Case insensitive search
grep -r	Recursive search
grep -v	Inverted search
grep -C <num>	print <num> lines before and after the match line
cmd 1>&2	stdout to same place as stderr
cmd 2>&1	stderr to same place as stdout
!!	Repeat last command
!abc	Run last command starting with abc
head -n1 /etc/issue	Show distribution
CTRL-a	Go to the start of line
CTRL-e	Go the the end of line
CTRL-u	Cut from start of line
CTRL-k	Cut to end of line
Ctrl + w	delete from cursor to start of word (i.e. delete backwards one word)
Ctrl + y	paste word or text that was cut using one of the deletion shortcuts (such as the one above) after the cursor
Ctrl + xx	move between start of command line and current cursor position (and back again)
Ctrl + r	search the history backwards
Ctrl + g	escape from history searching mode
Ctrl + p	previous command in history (i.e. walk back through the command history)
Ctrl + n	next command in history (i.e. walk forward through the command history)
CTRL-d	Log out from a shell (similar to exit). EOF (end-of-file). This also terminates input form stdin.
CTRL-l	clear the terminal screen
CTRL-z	Sleep program
bg	Run the sleep program at background
fg	Bring the program from background to foreground
! !	run last command
!blah	run the most recent command that starts with ‘blah’ (e.g. !ls)
!blah:p	print out the command that !blah would run (also adds it as the latest command in the command history)
!$	the last word of the previous command (same as Alt + .)
!$:p	print out the word that !$ would substitute
!*	the previous command except for the last word (e.g. if you type ‘find some_file.txt /‘, then !* would give you ‘find some_file.txt‘)
!*:p	print out what !* would substitute

Remove bed file name: rm – -badfilename

Reference Cards

IF/ELIF/ELSE/FI

if [ "$animal" == "penguin" ]; then
  echo "Hmmmmmm fish... Tux happy!"
elif [ "$animal" == "dolphin" ]; then
  echo "Pweetpeettreetppeterdepweet!"
else
  echo "*prrrrrrrt*"
fi

Check comand return value

/pagh/script.sh
case $? in
  1)
    echo "return 1"
    ;;
  2)
    echo "return 2"
    ;;
  *)
    echo "return $?"
    ;;
esac

Integer comparison

Operator	Description	Example & comments
-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”))

String comparison

Operator	Description	Example & comments
=	is equal to	if [ “$a” = “$b” ] Note the whitespace framing the =. if [ “$a”=”$b” ] is NOT equivalent to the above.
==	is equal to	if [ “$a” == “$b” ] There is a synonym for =. The == comparison operator behaves differently within a double-brackets test than with in single brackets. [[ $a == z* ]] # True if $a starts with an “z” (pattern matching) [[ $a == “z*” ]] # True if $a is equal to z* (literal matching) [ $a == z* ] # File globbing and word splitting take place. [ “$a” == “$z” ] # True if $a is equal to z* (literal matching)
!=	is not equal to	if[ “$a” != “$b” ] This operator uses pattern matching with in a [[ … ]] construct.
<	is less than, in ASCII alphabetical order	if [[ “$a” < “$b” ]] if [ “$a” < “$b” ] Note that the “<” needs to be escaped within a [ … ] construct.
>	is great than, in ASCII alphabetical order	if [[ “$a” > “$b” ]] if [ “$a” > “$b” ] Note that the “>” needs to be escaped within a [ … ] construct.
-z	string is null, that is, has zero length	String=’’ # Zero-length (“null”) string variable. if [ -z “$String” ]
-n	strint is not null

Special Shell Variable

Variable	Meaning
$0	Filename of script
$1	Positional parameter #1
$2 - $9	Positional parameters #2 - #9
${10}	Positional parameter #10
$#	Number of positional parameters
”$*”	All the positional parameters (as a single word) *
”$@”	All the positional parameters (as separate strings)
${#*}	Number of positional parameters
${#@}	Number of positional parameters
$?	Return value
$$	Process ID (PID) of script
$-	Flags passed to script (using set)
$_	Last argument of previous command
$!	Process ID (PID) of last job run in background

Files test operators

Operator	Tests Whether	—–	Operator	Tests Whether
-e	File exists		-s	File is not zero size
-f	File is a regular file
-d	File is a directory		-r	File has read permission
-h	File is a symbolic link		-w	File has write permission
-L	File is a symbolic link		-x	File has execute permission
-b	File is a block device
-c	File is a character device		-g	sgid flag set
-p	File is a pipe		-u	suid flag set
-S	File is a socket		-k	“sticky bit” set
-t	File is associated with a terminal
-N	File modified since it was last read		F1 -nt F2	File F1 is newer than F2
-O	You own the file		F1 -ot F2	File F1 is older than F2
-G	Group id of file same as yours		F1 -ef F2	Files F1 and F2 are hard links to the same file
!	NOT (inverts sense of above tests)

Reference: http://tldp.org/LDP/abs/html/