Regular expressions

1.1. Cheatsheet

Image Regex Cheatsheet (MIT)
Image Davechild Regular Expressions (Cheatography)

1.2. QuickStart

From http://www.rexegg.com/regex-quickstart.html

Character Legend Example Sample Match
\d One digit file_\d\d file_25
\w One "word character": letter, underscore or digit \w-\w\w\w A-b_1
\s One white space character (e.g.: a tab) ab\s\s\sc ab   c
\D One character that is not a digit \D\D\D ABC
\W One character that is not a word character \W\W\W\W\W *-+=)
\S One character that is not a space \S\S\S\S Yoyo

 

Quantifier Legend Example Sample Match
+ One or more Version \w-\w+ Version A-b1_1
{3} Exactly three times \D{3} ABC
{2,4} Two to four times \d{2,4} 156
{3,} Three or more times \w{3,} regex_tutorial
* Zero or more times A*B*C* AAACC
? Once or none plurals? plural

 

Character Legend Example Sample Match
. Any character except new line a.c abc
. Any character except new line .* whatever, man.
\. A period (special character: needs to be escaped by a \) a\.c a.c
\ Escapes a special character \.\*\+\?    \$\
\/\\
 .*+?    $/\
\ Escapes a special character \\{\(\)\}\ {()}

 

Logic Legend Example Sample Match
| OR operand 22|33 33
() Capturing group A(nt|pple) Apple (captures "pple")
\1 Contents of Group 1 r(\w)g\1x regex
\2 Contents of Group 2 (\d\d)\+(\d\d)=\2\+\1 12+65=65+12
(?: Non-capturing group A(?:nt|pple) Apple

 

Character Legend Example Sample Match
\t Tab T\t\w{2} T     ab
\r Return character see below  
\n New line character see below  
\r\n New line in Windows AB\r\nCD AB
CD

 

Quantifier Legend Example Sample Match
+ The + (one or more) is "greedy" \d+ 12345
? Makes quantifiers "lazy" \d+? 1 in 12345
* The * (zero or more) is "greedy" A* AAA
? Makes quantifiers "lazy" A*? empty in AAA
{2,4} Two to four times, "greedy" \w{2,4} abcd
? Makes quantifiers "lazy" \w{2,4}? ab in abcd

 

Character Legend Example Sample Match
stuff One of the characters in the brackets AEIOU One uppercase vowel
- Range indicator a-z One lowercase letter
stuff One of the characters in the brackets AB1-5w-z One of either: A,B,1,2,3,4,5,w,x,y,z
stuff One of the characters in the brackets A-Z+ GREAT
^x One character that is not x ^a-z{3} A1!
\d\D One character that is a digit or a non-digit \d\D+ Any characters, inc-
luding new line

 

Anchor Legend Example Sample Match
Beginning of line (but means "not" inside ^brackets) abc .* abc (line start)
$ End of line .*? the end$ this is the end
\A Beginning of string \Aabc\d\D* abc (string...
...start)
\Z End of string \d\D*the end\Z this is...
...the end
\b Word boundary Bob.*\bcat\b Bob ate the cat
\B Not a word boundary Bob.*\Bcat\B.* Bobcats

 

Character Legend Example Sample Match
:alpha: Letters [8:alpha:]+ WellDone88
:alnum: Letters and numbers [[:alnum:]]{10} ABCDE12345
:punct: Punctuation marks [[:punct:]]+ ?!.,:;

 

Modifier Legend Example Sample Match
(?i) Case-insensitive (?i)Monday monDAY
(?s) The dot (.) matches new line characters (\r\n) (?s)From A.*to Z From A
to Z
(?m) Treats the string as multiple lines, so that
and $ can match in several places
 (?m)1\r\n2$\r\n^3$ 1
2
3
(?x) Comment mode (aka whitespace mode) (?x) # this is a
# comment
abc # write on multiple
# lines
d # spaces must be
# in brackets		 abc d

 

Lookaround Legend Example Sample Match
(?= Positive lookahead (?=\d{10})\d{5} 01234 in0123456789
(?<= Positive lookbehind (?<=\d)cat cat in 1cat
(?! Negative lookahead (?!theatre)the\w+ theme
(?<! Negative lookbehind \w{3}(?<!mon)ster Munster
 

1.3. Styles

There perls & bash regexp styles, which are the common ones, maybe. There are other styles (vim, R, ...), but I don't plan to be fully comprehensive, here, since most styles are similar or can be run in perl-style with some flag/param/argument.

1.4. Ubuntu

Packages in Ubuntu 13.10 to help with regular expressions:

1.4.1. codeblocks-contrib: Regular expression testbed

http://codeblocks.org

Click to expand
Click to expand


Plugin regexp for Codeblocks editor (Regular expression testbed)

1.4.2. kiki: Tool for python regular expression testing

http://project5.freezope.org/kiki (broken)

Click to expand
Click to expand


A free environment for regular expression testing (ferret). It allows you to write regexes and test them against a sample text, providing
extensive output about the results. It is useful for several purposes:

  • exploring and understanding the structure of match objects generated by the re module, making Kiki a valuable tool for people new to regexes.
  • testing regexes on sample text before deploying them in code.


Kiki can function on its own or as plugin for the Spe Python editor.

1.4.3. redet: regular expression development and execution tool

http://www.billposer.org/Software/redet.html

Click to expand
Click to expand

Redet allows the user to construct regular expressions and test them against input data by executing any of a variety of search programs, editors, and programming languages that make use of regular expressions. When a suitable regular expression has been constructed it may be saved to a file.

Redet stands for Regular Expression Development and Execution Tool. For each program, a palette showing the available regular expression syntax is provided. Selections from the palette may be copied to the regular expression window with a mouse click. Users may add their own definitions to the palette via their initialization file. Redet also keeps a list of the regular expressions executed, from which entries may be copied back into the regular expression under construction. The history list is saved to a file and restored on startup, so it persists across sessions.

So long as the underlying program supports Unicode, Redet allows UTF-8 Unicode in both test data and regular expressions.

1.4.4. rgxg: command-line tool to generate regular expressions

http://rgxg.sf.net
rgxg (ReGular eXpression Generator) is a command-line tool to generate (extended) regular expressions.

It can be useful to generate (extended) regular expressions to match for instance a specific number range (e.g. 0 to 31 or 00 to FF) or all addresses of a CIDR block (e.g. 192.168.0.0/24 or 2001:db8:aaaa::/64). 


xavi@coprinus:~$ rgxg
Usage: rgxg COMMAND [ARGS]

The available rgxg commands are:
  alternation     Create regex that matches any of the given patterns
  cidr            Create regex that matches all addresses of the given CIDR block
  escape          Escape the given string for use in a regex
  range           Create regex that matches integers in a given range

Type 'rgxg help COMMAND' for help information on a specific command.

Type 'rgxg version' to see the version of rgxg.
xavi@coprinus:~$ rgxg help escape
Usage: rgxg escape [options] STRING

    -h         display this help message

1.4.5. txt2regex: A Regular Expression "wizard", all written with bash2 builtins

Click to expand
Click to expand

^txt2regex$ is a Regular Expression "wizard", all written with bash2 builtins, that converts human sentences to RegExs. With a simple interface, you just answer to questions and build your own RegEx for a large variety of programs, like awk, emacs, grep, perl, php, procmail, python, sed and vim. There are more than 20 supported programs.

1.4.6. visual-regexp: Interactively debug regular expressions

http://laurent.riesterer.free.fr/regexp/

Click to expand
Click to expand

This Tcl script shows the result of running a regular expression, making debugging relatively easy. It also assists in the construction
of regular expressions.

1.5. PHP online live regexp help

https://www.phpliveregex.com/

1.6. Online tools


Alias names for this page:
regexp | regexps | Regular Expression | regexpr

Comments
Image Seed: noun \ˈsēd\ : the beginning of something which continues to develop or grow

Knowledge seeds

Switch Language