Bash Regular Expression Cheat Sheet

admin | 30-04-2021

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For use in [ ]if [ ]; then and test.

Bash Regular Expression Cheat Sheet
Bash Cheat Sheet
Bash Regular Expression List
Bash Regular Expression Examples
Bash Regular Expression Replace

Man$command’:$displaythecommand’s(manualpage( JacquesDainat(5(2015(BASH cheat sheet - $Level 2 Wildcards Miscellaneous ’ (Escape(character.Itpreserves(the. With bash, an expression is normally enclosed using and can use the following operators, in order of precedence. » Bash Cheat Sheet Johns Blog Page 4 of 4. Bash Regex Cheat Sheet Edit Cheat Sheet Regexp Matching. Use conditions with doubled and the = operator. Ensure not to quote the regular expression. Only BRE are allowed. If the regexp has whitespaces put it in a variable first.

Note: When writing a bash or zsh script, use [[ instead of POSIX [.

Variable conditionals

Use these to check if a variable is empty or non-empty.

Expression	Value	Description
`-n`	`var`	If the length of string is non-zero.
`-z`	`var`	If the length of string is zero.

Variable comparisons

String:

Expression	Description
`var1 = var2`	Equal to.
`var1 != var2`	Not equal to.

Note: Use instead of = inside of [[ for bash, zsh scripts.

Numeric:

Expression	Description
`var1 -eq var2`	Equal to.
`var1 -ne var2`	Not equal to.
`var1 -gt var2`	Greater than.
`var1 -ge var2`	Greater than or equal to.
`var1 -lt var2`	Less than.
`var1 -le var2`	Less than or equal to.

File conditionals

Common:

Expression	Value	Description
`-e`	`file`	If file exists and is any type.
`-f`	`file`	If file exists and is a regular file.
`-d`	`file`	If file exists and is a directory.
`-h`/`-L`	`file`	If file exists and is a symbolic link.
`-r`	`file`	If file exists and is readable.
`-w`	`file`	If file exists and is writable.
`-x`	`file`	If file exists and is executable.
`-s`	`file`	If file exists and has non-zero size (is non-empty).

Bash Regular Expression Cheat Sheet

Rare:

Expression	Value	Description
`-b`	`file`	If file exists and is a block special file.
`-c`	`file`	If file exists and is a character special file.
`-g`	`file`	If file exists and its set-group-id bit is set.
`-p`	`file`	If file exists and is a named pipe (FIFO).
`-t`	`fd`	If file descriptor is open and refers to a terminal.
`-u`	`file`	If file exists and its set-user-id bit is set.
`-S`	`file`	If file exists and is a socket.

Assignment

Operator	Description
`=`	Initialize or change the value of a variable.

Logical

Bash Cheat Sheet

Operator	Description
`!`	NOT
`&&`	AND
`\|\|`	OR

Arithmetic

Operator	Description
`+`	Addition
`-`	Subtraction
`*`	Multiplication
`/`	Division
`**`	Exponentiation
`%`	Modulo
`+=`	Plus-Equal
`-=`	Minus-Equal
`*=`	Times-Equal
`/=`	Slash-Equal
`%=`	Mod-Equal

Use these in place of awk or sed calls when possible.

Replacement

Parameter	Description
`${VAR//PATTERN/REPLACE}`	Substitute pattern with replacement.
`${VAR#PATTERN}`	Remove shortest match of pattern from start.
`${VAR##PATTERN}`	Remove longest match of pattern from start.
`${VAR%PATTERN}`	Remove shortest match of pattern from end.
`${VAR%%PATTERN}`	Remove longest match of pattern from end.

Length

Parameter	Description
`${#VAR}`	Length of var in characters.

Default Value

Parameter	Description
`${VAR:-STRING}`	If `VAR` is empty or unset, use `STRING` as its value.
`${VAR-STRING}`	If `VAR` is unset, use `STRING` as its value.
`${VAR:=STRING}`	If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
`${VAR=STRING}`	If `VAR` is unset, set the value of `VAR` to `STRING`.
`${VAR:+STRING}`	If `VAR` is not empty, use `STRING` as its value.
`${VAR+STRING}`	If `VAR` is set, use `STRING` as its value.
`${VAR:?STRING}`	Display an error if empty or unset.
`${VAR?STRING}`	Display an error if unset.

Text Colors

Note: Sequences using RGB values only work in 24-bit true-color mode.

Sequence	Description	Value
`033[38;5;<NUM>m`	Set text foreground color.	`0-255`
`033[48;5;<NUM>m`	Set text background color.	`0-255`
`033[38;2;<R>;<G>;<B>m`	Set text foreground color to RGB color.	`R`, `G`, `B`
`033[48;2;<R>;<G>;<B>m`	Set text background color to RGB color.	`R`, `G`, `B`

Text Attributes

Sequence	Description
`033[m`	Reset text formatting and colors.
`033[1m`	Bold text.
`033[2m`	Faint text.
`033[3m`	Italic text.
`033[4m`	Underline text.
`033[5m`	Slow blink.
`033[7m`	Swap foreground and background colors.
`033[8m`	Hidden text.
`033[9m`	Strike-through text.

Variable	Description
`$-`	Shell options
`$$`	Current shell PID

For use in [ ]if [ ]; then and test.

Note: When writing a bash or zsh script, use [[ instead of POSIX [.

Variable conditionals

Bash Regular Expression List

Use these to check if a variable is empty or non-empty.

Expression	Value	Description
`-n`	`var`	If the length of string is non-zero.
`-z`	`var`	If the length of string is zero.

Variable comparisons

String:

Expression	Description
`var1 = var2`	Equal to.
`var1 != var2`	Not equal to.

Note: Use instead of = inside of [[ for bash, zsh scripts.

Numeric:

Expression	Description
`var1 -eq var2`	Equal to.
`var1 -ne var2`	Not equal to.
`var1 -gt var2`	Greater than.
`var1 -ge var2`	Greater than or equal to.
`var1 -lt var2`	Less than.
`var1 -le var2`	Less than or equal to.

File conditionals

Bash regular expression examples

Common:

Expression	Value	Description
`-e`	`file`	If file exists and is any type.
`-f`	`file`	If file exists and is a regular file.
`-d`	`file`	If file exists and is a directory.
`-h`/`-L`	`file`	If file exists and is a symbolic link.
`-r`	`file`	If file exists and is readable.
`-w`	`file`	If file exists and is writable.
`-x`	`file`	If file exists and is executable.
`-s`	`file`	If file exists and has non-zero size (is non-empty).

Rare:

Expression	Value	Description
`-b`	`file`	If file exists and is a block special file.
`-c`	`file`	If file exists and is a character special file.
`-g`	`file`	If file exists and its set-group-id bit is set.
`-p`	`file`	If file exists and is a named pipe (FIFO).
`-t`	`fd`	If file descriptor is open and refers to a terminal.
`-u`	`file`	If file exists and its set-user-id bit is set.
`-S`	`file`	If file exists and is a socket.

Assignment

Operator	Description
`=`	Initialize or change the value of a variable.

Logical

Operator	Description
`!`	NOT
`&&`	AND
`\|\|`	OR

Arithmetic

Operator	Description
`+`	Addition
`-`	Subtraction
`*`	Multiplication
`/`	Division
`**`	Exponentiation
`%`	Modulo
`+=`	Plus-Equal
`-=`	Minus-Equal
`*=`	Times-Equal
`/=`	Slash-Equal
`%=`	Mod-Equal

Use these in place of awk or sed calls when possible.

Replacement

Parameter	Description
`${VAR//PATTERN/REPLACE}`	Substitute pattern with replacement.
`${VAR#PATTERN}`	Remove shortest match of pattern from start.
`${VAR##PATTERN}`	Remove longest match of pattern from start.
`${VAR%PATTERN}`	Remove shortest match of pattern from end.
`${VAR%%PATTERN}`	Remove longest match of pattern from end.

Length

Parameter	Description
`${#VAR}`	Length of var in characters.

Default Value

Parameter	Description
`${VAR:-STRING}`	If `VAR` is empty or unset, use `STRING` as its value.
`${VAR-STRING}`	If `VAR` is unset, use `STRING` as its value.
`${VAR:=STRING}`	If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
`${VAR=STRING}`	If `VAR` is unset, set the value of `VAR` to `STRING`.
`${VAR:+STRING}`	If `VAR` is not empty, use `STRING` as its value.
`${VAR+STRING}`	If `VAR` is set, use `STRING` as its value.
`${VAR:?STRING}`	Display an error if empty or unset.
`${VAR?STRING}`	Display an error if unset.

Bash Regular Expression Examples

Text Colors

Bash Regular Expression Replace

Note: Sequences using RGB values only work in 24-bit true-color mode.

Sequence	Description	Value
`033[38;5;<NUM>m`	Set text foreground color.	`0-255`
`033[48;5;<NUM>m`	Set text background color.	`0-255`
`033[38;2;<R>;<G>;<B>m`	Set text foreground color to RGB color.	`R`, `G`, `B`
`033[48;2;<R>;<G>;<B>m`	Set text background color to RGB color.	`R`, `G`, `B`

Text Attributes

Sequence	Description
`033[m`	Reset text formatting and colors.
`033[1m`	Bold text.
`033[2m`	Faint text.
`033[3m`	Italic text.
`033[4m`	Underline text.
`033[5m`	Slow blink.
`033[7m`	Swap foreground and background colors.
`033[8m`	Hidden text.
`033[9m`	Strike-through text.

Variable	Description
`$-`	Shell options
`$$`	Current shell PID