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Regex Regular Expression Snippets

Source: Regular expression syntax cheat sheet - JavaScript | MDN - Regex syntax and explanations with examples

Terminal window
# Match any single character except new line, like a wild card
.


# Quatifiers + * and ? can be used with matches, groups
# Match 1 or many characters with +
.+
# Match 0 or more characters with *
.*
# Match 0 or 1 character with ?
.?


# Match digits (numbers)
\d
# Match digit pattern, like a phone number
\d\d\d-\d\d\d-\d\d\d\d
# Match digit pattern, like a phone number using quantifier
\d{3}-\d{3}-\d{4}


# Match exactly 4 word characters
^\w{4}$


# Match non digits
\D


# Match word boundary, where word character not followed or preceded by another word character
\b


# Match word character, includes [a-zA-Z0-9_] alpha, number, and underscore characters
\w


# Match 1 or more word characters
\w+


# Match a character optionally with <char>?
ab?c
## Matches abc and ac since b is optional


# Match exact word
'jump'
## Matches jump inside jumped or jump by itself


# Match word itself with \b, not surrounded by other characters
'\bfor\b'


# Match 1 or more digits
\d+


# Match any 1 character in a given set using [ ]
[abc]
# Match to a, b, or c, also called character group


# Match either of defined character groups using (  )
Jo(n|hn)
## | is for or
## Match John or Jon for alternate spellings
I love (cat|dog)s


# Group for matching and can be used operations like replace
\d{3}-\d{3}-(\d{4})
## Use a phone number pattern and group last 4 digits


# Group multiple elements with capture groups
(\d{3})-(\d{3})-(\d{4})
## 3 groups will be created for text operations


# Named capture groups
?<areacode>^(\d{3})-(\d{3})-?<last4digits>(\d{4}$)


# Reference capture groups (depends on implementation) with \#
\1
## Capture group 1 with \1
## Capture group 2
\2


# Match words consisting of the same letter repeating exactly 3 times
^([a-zA-Z])\1{2}
# First (brackets) matches a letter, \1 will reference the capture group
# and {2} indicates only match capture group 1, two more times


# Match not characters group
[^dog]
## ^ matches not in character group


# Match ranges
# Match lower case alphabet characters
[a-z]
[n-p]
# Match to not a range
[^a-t]
# Match multiple ranges
[a-z][a-z]
## Matchs any 2 lower case characters together
# Match upper case alpha characters
[A-Z]
# Match numbers 0 through 9
[0-9]
# Match multiple ranges in a single character group
[a-zA-Z0-9]
## Matches all upper and lowercase alpha characters and numbers


# Match start of string with ^
^The


# Match end of string with $
dog$


# Match start and end strings
^The.+dog$
# ^ match start
# .+ 1 or more characters
# $ match end


# Match a specific {number}, or {min,} or {min,max} with quantifiers
^a.{5}g$
## {5} matches exactly 5 characters between a and g
^a.{1,}g$
## {1,} matches at minimum 1 character but can be more
^a.{0,5}g$
## {0,5} matches at minimum 0 characters and maximum 5


# Search for the words "apple" and "banana" in any order
^(?=.*apple)(?=.*banana).*


# search for apple, banana and/or cherry in any order
^(?=.*apple)(?=.*banana)(?=.*cherry).*


# Check an email address, simplified, doesn't work for all emails
^[a-zA-Z0-9]+@[a-zA-Z0-9]+\.[a-zA-Z0-9]+$
## ^[a-zA-Z0-9]+ match start with 1 or more of character group
## @ match @ character
## \. match . character itself, needs to be escaped, not regex character
## [a-zA-Z0-9]+$ match ending domain of email
## See RFC 5322 for official email regex


# Escaped characters [ ] \ with \
\[part\]backslash_coming\\
# Escape plus (+) sign with \, works for other symbols
\+


# Match tab
\t


# Match newline
\n


# Match whitespace character
\s


# Match non-whitespace character
\S


# Match any character
[\s\S]


# Match with constraint using ?, "lazy" matching
([\s\S])*?[ \t]*
## Lazy matching means only match the minimum
## The match will match whitespace and non whitespact characters
## to allow other match groups to match further items
## *? will match the first set 0 or more and allow further
## tabs and spaces to match
## Without ?, ([\s\S])* will match all instances and not leave
## matches for other matches, it's greedy


## Example <div class="hello">My text</div>
## Match My text
[\s\S]*?<div class"hello">([\s\S]*?)</div>
## Match 0 or more any character lazily, then div tag
## then match text inside div tag lazily, then match closing tag


# Match with no constraint, match all available with +
([0-9]*+)([0-9]{2})
## In a long number, ([0-9]*+) will match all numbers and not
## leave any matches for the 2nd part
## Using *? will leave matches for the [0-9]{2}


# Match with look behind with ?<=pattern
(?<=\$)\d+
## Look behind the $ symbol for digits


## For example, A pizza is $10.99 today.
## Match will look behind $ and get 10.99
(?<=\$)\d+(\.\d{2})?
## Same match, but do not capture the second group to improve efficiency
(?<=\$)\d+?(\.\d{2})?


# Match with look behind not with (?<!)
(?<!\$\d+)
## Match for digits when not preceded by a $ sign


# Match with look ahead with ?=pattern
\d+(?=pattern)


# Match with look ahead with ?!pattern
\d+(?!pattern)


# Match

Examples of Testing Regex setup

Section titled “Examples of Testing Regex setup”

Examples above and tests follow closely from this source: A look at using Regular Expressions (RegEx) - John Savill’s Technical Training on YouTube

Install grep or ripgrep for tests

Terminal window
# Create a file with a sentence for using regex
cat <<EOF > test.md
The quick brown fox jumped over the lazy dog
EOF


# Use grep with regex PATTERN on current directory
grep PATTERN *


# Recursively (-r) search current directory
grep -r 'f.x'
# . will match only 1 of any character


# Match fox or fix using character group
grep -r 'f[io]x'

See Also

Section titled “See Also”

Resources

Section titled “Resources”