Bash Operators Cheat Sheet

Table of Contents

• 1. 1. File Test Operators
• 2. 2. String Comparison Operators
• 3. 3. Numeric Comparison Operators
• 4. 4. Logical Operators
• 5. 5. Arithmetic Operators
• 6. 6. Assignment Operators
• 7. 7. Bitwise Operators
• 8. 8. Process Control Operators
• 9. Conclusion

This cheat sheet covers Bash operators including file tests, string comparisons, logical operations, and arithmetic evaluations.

1. 1. File Test Operators

File test operators check the status of files.

Operator	Description	Example
-e	File exists (any type)	[[ -e file.txt ]]
-f	File exists and is a regular file	[[ -f script.sh ]]
-d	File exists and is a directory	[[ -d myfolder ]]
-r	File is readable	[[ -r data.txt ]]
-w	File is writable	[[ -w output.log ]]
-x	File is executable	[[ -x script.sh ]]
-s	File exists and is not empty	[[ -s nonempty.txt ]]
-L	File is a symbolic link	[[ -L shortcut ]]
-b	File is a block device	[[ -b /dev/sda1 ]]
-c	File is a character device	[[ -c /dev/ttyS0 ]]
-p	File is a named pipe (FIFO)	[[ -p pipefile ]]
-S	File is a socket	[[ -S /var/run/docker.sock ]]

2. 2. String Comparison Operators

Used to compare strings in conditional expressions.

Operator	Description	Example
-z	String is empty	[[ -z "$var" ]]
-n	String is not empty	[[ -n "$var" ]]
=	Strings are equal	[[ "$a" = "$b" ]]
!=	Strings are not equal	[[ "$a" != "$b" ]]
>	String a is greater than b (lexically)	[[ "$a" > "$b" ]]
<	String a is less than b (lexically)	[[ "$a" < "$b" ]]

3. 3. Numeric Comparison Operators

Used in …​ arithmetic evaluations and [ …​ ] test conditions.

Operator	Description	Example
-eq	Equal to	[[ "$a" -eq "$b" ]]
-ne	Not equal to	[[ "$a" -ne "$b" ]]
-lt	Less than	[[ "$a" -lt "$b" ]]
-le	Less than or equal to	[[ "$a" -le "$b" ]]
-gt	Greater than	[[ "$a" -gt "$b" ]]
-ge	Greater than or equal to	[[ "$a" -ge "$b" ]]

4. 4. Logical Operators

Used to combine conditions.

Operator	Description	Example
&&	Logical AND (both must be true)	[[ -f file.txt && -r file.txt ]]
||	Logical OR (either can be true)	[[ -d mydir || -f myfile ]]
!	Logical NOT (negation)	[[ ! -e missing.txt ]]
-a	Logical AND (deprecated)	[[ -f file.txt -a -r file.txt ]]
-o	Logical OR (deprecated)	[[ -d mydir -o -f myfile ]]

5. 5. Arithmetic Operators

Used inside …​ for integer calculations.

Operator	Description	Example
+	Addition	sum = a + b
-	Subtraction	diff = a - b
*	Multiplication	product = a * b
/	Division	quotient = a / b
%	Modulus (remainder)	remainder = a % b
**	Exponentiation	power = a ** b
++	Increment	a++
--	Decrement	b--

6. 6. Assignment Operators

Used to assign values to variables.

Operator	Description	Example
=	Assign value	a=5
+=	Add and assign	a+=2 # a = a + 2
-=	Subtract and assign	b-=3 # b = b - 3
*=	Multiply and assign	c*=4 # c = c * 4
/=	Divide and assign	d/=2 # d = d / 2
%=	Modulus and assign	e%=3 # e = e % 3
**=	Exponentiate and assign	f=2 # f = f 2

7. 7. Bitwise Operators

Used for bitwise manipulation.

Operator	Description	Example
&	AND	result = a & b
|	OR	result = a | b
^	XOR	result = a ^ b
~	NOT	result = ~a
<<	Left shift	result = a << 2
>>	Right shift	result = a

8. 8. Process Control Operators

Used to control execution flow.

Operator	Description	Example
;	Run multiple commands sequentially	echo "Hello"; echo "World"
&	Run command in the background	sleep 10 &
&&	Run next command if previous succeeds	mkdir test && cd test
`		`
Run next command if previous fails	`rm file
echo "File not found"`	`	`
Pipe output of one command to another	`ls -l	grep ".txt"`
>	Redirect output to a file (overwrite)	echo "Hello" > file.txt
>>	Redirect output to a file (append)	echo "World" >> file.txt
<	Read input from a file	sort < input.txt
2>	Redirect stderr to a file	command 2> error.log
2>&1	Redirect stderr to stdout	command > output.log 2>&1
&>	Redirect both stdout and stderr to a file	command &> log.txt
$(command)	Command substitution	current_date=$(date)
	Arithmetic evaluation	result = a + b
[[ ]]	Advanced test command	[[ -f file.txt ]]
{ }	Group commands in the current shell	{ echo "One"; echo "Two"; }
( )	Group commands in a subshell	(cd /tmp; ls)

9. Conclusion

This cheat sheet provides a quick reference for Bash operators. Mastering these will help you write efficient shell scripts.