===== Bash quick reference =====

^Command	^Description	^Example     ^
|&	|Run the previous command in the background	|ls & |
|&&	|Logical AND	|if [ "$foo" -ge "0" ] && [ "$foo" -le "9"] |
|%%||%%	|Logical OR	|if [ "$foo" -lt "0" ] %%||%% [ "$foo" -gt "9" ] (not in Bourne shell) |
|%%^%%	|Start of line	|grep "%%^%%foo" |
||$	|End of line	|grep "foo$" |
|=	|String equality (cf. -eq) |if [ "$foo" = "bar" ] |
|!	|Logical NOT	|if [ "$foo" != "bar" ] |
|$$	|PID of current shell	|echo "my PID = $$" |
|$!	|PID of last background command	|ls & echo "PID of ls = $!" |
|$?	|exit status of last command	|ls ; echo "ls returned code $?" |
|$0	|Name of current command (as called)	|echo "I am $0" |
|$1	|Name of current command's first parameter	|echo "My first argument is $1" |
|$9	|Name of current command's ninth parameter	|echo "My ninth argument is $9" |
|$@	|All of current command's parameters (preserving whitespace and quoting)	|echo "My arguments are $@" |
|$*	|All of current command's parameters (not preserving whitespace and quoting)	|echo "My arguments are $*" |
|parenthesis: ( ... )	|Function definition	|function myfunc() { echo hello }|
|-b	|block special file	|if [ -b filename ] |
|-c	|Special character file|if [ -c filename ] |
|-d	|Is a Directory	|if [ -d /bin ] |
|-e	|Is file exist	|if [ -e /bin/ls ] |
|-eq	|Numeric Equality	|if [ "$foo" -eq "9" ] |
|-f	|Is a File	|if [ -f /bin/ls ] |
|-G	|check if file exists and is owned by effective groupid	|if [ -G /bin/ls ] |
|-g	|true if file exists and is set-group-id	|if [ -g /bin/ls ] |
|-ge	|Greater Than or Equal	|if [ "$foo" -ge "9" ] |
|-gt	|Greater Than	|if [ "$foo" -gt "9" ] |
|-k	|check sticky bit	|if [ -k /bin/ls ] |
|-L	|if file a symbolic link	|if [ -L /etc/alternatives/editor ] |
|-le	|Less Than or Equal	|if [ "$foo" -le "9" ] |
|-lt	|Less Than	|if [ "$foo" -lt "9" ] |
|-n	|String is not zero length	|if [ -n "$foo" ] |
|-ne	|Not Equal	|if [ "$foo" -ne "9" ] |
|-nt	|Newer Than	|if [ "$file1" -nt "$file2" ] |
|-O	|True if file exists and is owned by the effective user id	|if [ -O file ] |
|-r	|Is a readable file	|if [ -r /bin/ls ] |
|-s	|if file is nonzero size	|if [ -s /bin/ls ] |
|-S	|if file is a socket	|if [ -S file ] |
|-u	|check if file set-user-id bit is set  |if [ -u /bin/ls ] |
|-w	|Is a writable file	|if [ -w /bin/ls ] |
|-x	|Is an executable file	|if [ -x /bin/ls ] |
|-z	|String is zero length	|if [ -z "$foo" ] |