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 }