Unix / Linux Shell Scripting Tutorial

15. Quick Reference

This is a quick reference guide to the meaning of some of the less easily guessed commands and codes.

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 $*"`
-eq	Numeric Equality	`if [ "$foo" -eq "9" ]`
-ne	Numeric Inquality	`if [ "$foo" -ne "9" ]`
-lt	Less Than	`if [ "$foo" -lt "9" ]`
-le	Less Than or Equal	`if [ "$foo" -le "9" ]`
-gt	Greater Than	`if [ "$foo" -gt "9" ]`
-ge	Greater Than or Equal	`if [ "$foo" -ge "9" ]`
-z	String is zero length	`if [ -z "$foo" ]`
-n	String is not zero length	`if [ -n "$foo" ]`
-nt	Newer Than	`if [ "$file1" -nt "$file2" ]`
-d	Is a Directory	`if [ -d /bin ]`
-f	Is a File	`if [ -f /bin/ls ]`
-r	Is a readable file	`if [ -r /bin/ls ]`
-w	Is a writable file	`if [ -w /bin/ls ]`
-x	Is an executable file	`if [ -x /bin/ls ]`
parenthesis: ( ... )	Function definition	`function myfunc() { echo hello }`