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regular_expression.md

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String Match

  1. Match Once re: /ninja/
Strings Result Note
:--- :---: :---
ninja match
ninjawahwah match
ninja ninja match only match the FIRST ninja
  1. Global Match: g re: /ninja/g
Strings Result Note
:--- :---: :---
ninja ninja ninja ninja match match all 4 ninja
ninja ninja ninja Ninja match match first 3 ninja, except the last one, case-sensitive
  1. Case-insenstive Match: i re: /ninja/i
Strings Result Note
:--- :---: :---
ninja Ninja NiNjA NINJA match match all 4 ninja

Pattern Match

Character Set: []

  1. re: /[ng]inja/g
Strings Result Note
:--- :---: :---
ninja ninja ninga ginga match match all 4 ninja
  1. re: /[abc123]/g
Strings Result Note
:--- :---: :---
abc3 match match the whole string
ab3e match match "ab3"
abcdef3 match match "abc3"
  1. re: /[abc123]000/g
Strings Result Note
:--- :---: :---
ab3e No
a000 b000 c000 2000 match match all the 4 strings
e000 No

Exclusive Set: [^]

  1. re: /[^p]000/g
Strings Result Note
:--- :---: :---
a000 b000 c000 2000 e000 match match the whole string
  1. re: /[^pe]000/g
Strings Result Note
:--- :---: :---
a000 b000 c000 2000 match match all the 4 strings
e000 No
  1. re: /[^pe2]000/g
Strings Result Note
:--- :---: :---
a000 b000 c000 match match all the 3 string
2000 e000 No

Ranges: -

  1. +: match at least once (1 or more times) re: /[0-9]+/
Strings Result Note
:--- :---: :---
0 01 02839483 match match all 3 strings
0 01 02839483 match match all 3 strings
  1. {}: Specify the specific match times re: /[0-9]{10}/ match [0-9] 10 times
Strings Result Note
:--- :---: :---
0123456789 match match [0-9] 10 times consecutively

re: /[a-z]{5}/ match [a-z] 10 times

Strings Result Note
:--- :---: :---
ninja hello match match [a-z] twice

re: /[a-z]{5, 8}/ match [a-z] 5 to 8 times

Strings Result Note
:--- :---: :---
ninja hello hellowow ninjas match match [a-z] 3 times

re: /[0-9]{5, 8}/ match [0-9] 5 to 8 times

Strings Result Note
:--- :---: :---
012345 match match [0-5] 6 times
01234567 match match [0-9] 8 times
012345678 Partially match match 0123457 except 8

re: /[0-9]{5,}/ match [0-9] at least 5 times, i.e., the string is at least 5 characters long

Strings Result Note
:--- :---: :---
012345678 match match [0-9] 9 times
0123456782384748 match

Metacharacters

Metacharacter Note
:--- :---
\d match any digit character, same as [0-9]
\w match any word character, same as a-z, A-Z, 0-9, and _ (underscore)
\s match a whitespace character (space, tab, etc)
\t match a tab character
  1. re: /\d/
Strings Result Note
:--- :---: :---
0 1 5 6 9 match

re: /\w/

Strings Result Note
:--- :---: :---
a v z A W match match all the characters
0 6 7 9 _ match match all the characters
@ No

re: /\s/

Strings Result Note
:--- :---: :---
SPACE TAB match match SPACE, TAB
RE Note
:--- :---
/\d\s\w/ match a string of (a digit + some whitespace + a word)
/\d{3}\s\w/{5} match a string of (3 digits + 1 whitespace + 5 words)

Special Characters

Character Note
:--- :---
+ match at least once (>=1 times)
\ escape character
[] match any characters in the character set
[^] match characters not in the character set
? match 0 or 1 time, make the preceding character optional
. match any character except a newline
* match 0 or more times
  1. ? re: /hello?/ making character 'o' optional
Strings Result Note
:--- :---: :---
hello hell match match the 2 strings

re: /he?llo?/ making character 'o' optional

Strings Result Note
:--- :---: :---
hello hllo hell hll match match the 4 strings

re: /a[a-z]?/ making character [a-z] optional

Strings Result Note
:--- :---: :---
a ab az match match the 3 strings
  1. dot (.) re: /car./ making character [a-z] optional
Strings Result Note
:--- :---: :---
car no needs to be 4-character long
cars card car@ match match the 3 strings

re: /.+/ any character except a newline, can be any length.

Strings Result Note
:--- :---: :---
a389^$#!F~934j###@#*** match

re: /a[a-z]*/ any character except a newline, can be any length.

Strings Result Note
:--- :---: :---
a abeid match
a abeid1234 Partially match match alphabets except digits
  1. Escape character:
    re: /abc*/ any character except a newline, can be any length.
RE
:--- :---
abc* abc*
abc+ abc+
abc. abc.

Start and Ending Characters

re: /[a-z]{5}/

String Result Note
:--- :---: :---
ninjaninjaninjaninja match match ninja once

re: /[a-z]{5}/g

String Result Note
:--- :---: :---
hello ninja world match match the 3 strings
ninjaninjaninjaninja match match 5 times of ninja
  1. ^ and $ re: /^[a-z]{5}$/g the string must have 5 characters
String Result Note
:--- :---: :---
hello ninja world match match the 3 strings
ninjaninjaninjaninja No

re: /[a-z]{5}$/g the string must have 5 characters

String Result Note
:--- :---: :---
ninjaninjaninjaninja Partially match Only match the last 5-characters

Alternative Character: | and Group ()

RE Note
:--- :---
/p t/
/p tyre/
/pyre tyre/
/(p t)yre/
/(pet toy
/(pet toy

ref: https://www.youtube.com/watch?v=m6iggPLGSMc&list=PL4cUxeGkcC9g6m_6Sld9Q4jzqdqHd2HiD