Shell Scripting Cheat Sheet

See python-specific-regex.md for python-specific identifiers.

Category	Syntax / Command	Description
Text Manipulation	echo "Hello, World!"	Prints text to the terminal.
Text Manipulation	printf "Name: %s\n" "Alice"	Formatted output.
Arithmetic	expr 5 + 3	Basic arithmetic.
Variables	VAR="value"	Assigns a value to a variable.
Loops	for i in {1..5}; do echo $i; done	For loop.
Control Flow	if [ "$x" -eq 10 ]; then echo "Yes"; fi	If statement.
Functions	my_func() { echo "Hello"; }	Defines a function.
File Operations	touch file.txt	Creates an empty file.
Process Management	ps aux	Lists running processes.
Redirections	command > file.txt	Redirects output to a file.
Pipes	command1 | command2	Pipes output of one command to another.

PCRE (Perl-Compatible Regular Expressions) Cheat Sheet

Pattern	Description	Example
.	Matches any single character (except newline).	/a.c/ matches "abc", "adc", "a#c"
\d	Matches any digit (0-9).	/\d+/ matches "123", "42"
\D	Matches any non-digit.	/\D+/ matches "abc", "hello"
\w	Matches any word character (a-z, A-Z, 0-9, _).	/\w+/ matches "hello_123"
\W	Matches any non-word character.	/\W+/ matches "!!!", "@@@"
\s	Matches any whitespace (space, tab, newline).	/\s+/ matches spaces
\S	Matches any non-whitespace character.	/\S+/ matches "word"
^	Matches the start of a line.	/^abc/ matches "abc" at start
$	Matches the end of a line.	/abc$/ matches "abc" at end
[abc]	Matches any character inside brackets.	/[aeiou]/ matches vowels
[^abc]	Matches any character NOT in brackets.	/[^0-9]/ matches non-digits
(...)	Capturing group.	/(hello)/ captures "hello"
|	Logical OR.	/cat|dog/ matches "cat" or "dog"
*	Matches 0 or more occurrences.	/a*/ matches "", "a", "aaa"
+	Matches 1 or more occurrences.	/a+/ matches "a", "aaa"
?	Matches 0 or 1 occurrences.	/a?/ matches "", "a"
{n}	Matches exactly n times.	/a{3}/ matches "aaa"
{n,}	Matches n or more times.	/a{2,}/ matches "aa", "aaa"
{n,m}	Matches between n and m times.	/a{2,4}/ matches "aa", "aaa", "aaaa"

Common Regex identifiers

Regex	Description	Example
.	Matches any single character except a newline (\n)	h.t matches hat, hit, but not h/t.
^	Anchors to the start of a string or line	^Hello matches "Hello" at the beginning of a string.
$	Anchors to the end of a string or line	world$ matches "world" at the end of a string.
\	Escape character for special symbols	\. matches a literal .
[]	Character class, matches any single character within	[aeiou] matches any vowel.
[^]	Negated character class, matches any single character not within	[^aeiou] matches any non-vowel.
|	Alternation (logical OR)
()	Capturing group; groups patterns and captures the match for later reference	(ab)+ matches "ab", "abab", etc.
(?: )	Non-capturing group; groups patterns without capturing them	(?:ab)+ matches "abab" but doesn’t capture it.
{}	Quantifier specifying exact or range repetitions	a{3} matches "aaa". a{2,4} matches "aa", "aaa", or "aaaa".
*	Matches 0 or more of the preceding character or group	a* matches "", "a", "aa", etc.
+	Matches 1 or more of the preceding character or group	a+ matches "a", "aa", etc., but not "".
?	Matches 0 or 1 of the preceding character or group; makes quantifiers lazy when placed after	a? matches "", or "a". a*? matches as few "a"s as possible.
/	Delimiter for regex in some languages like JavaScript or Perl	/hello/ matches "hello".
\d	Matches any digit (0-9)	\d{2} matches "12".
\D	Matches any non-digit	\D matches "a", but not "2".
\w	Matches any word character (alphanumeric + underscore)	\w+ matches "word123".
\W	Matches any non-word character	\W matches "@", but not "a".
\s	Matches any whitespace character (spaces, tabs, newlines)	\s+ matches spaces between words.
\S	Matches any non-whitespace character	\S+ matches "word123", but not " ".
\b	Matches a word boundary	\bword\b matches "word", but not "sword".
\B	Matches a position that is not a word boundary	\Bword matches "sword", but not " word".