Duncan Wither

Regex Cheat Sheet

Written: 05-Mar-2022

Regex is useful. This cheat-sheet is a condensation of Amit Chaudhary’s useful article. Also of note/inspiration is this regex cheat-sheet

cat matches any instance of the letters c then a then t. This includes both cat the word and the first three letters of cathartic.

There are some special chars for fun things…

Groups:

• [ab] - Matches a or b
• (ab) - Capture Group (like brackets in maths)
  • e.g. (png|jpg) matches png or jpg

Wildcards:

• . - Any char that’s not a new line (~= [a-zA-Z0-9])
• \d - Digit (~= [0-9])
• \w - Word char aka a letter (~=[a-zA-Z])
• \s - (White)space
• Capitalised versions (i.e. \D, \W, \S) invert the search.

Iterations:

• {n} - n times of prev. char
• * - Zero or more of prev. char (~={0,})
• + - One or more of prev. char (~={1,})
• ? - Zero or one of prev. char (~={0,1})

Anchors:

• ^ - Start of line
• $ - End of line

Special Chars

• \ - Escape char
  • e.g. looking for who? would require who\?

Lookaround (More Advanced)

If you want to match something thats defind by what or what does preced or procede then you need to use lookahead operators. There’s a good regex buddy article explaining this.

• q(?=u) - Positive look ahead (Queen not Qatar)
• q(?!u) - Negative look ahead (Qatar not Queen)
• a(?<=b) - Positive look behind: (lab not cub)
• a(?<!b) - Negative Look behind: (cub not lab)

Note look behind requires static length (no escapes or .*).

Online help

• A visual regex builder tool