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Groups

Use $& on the replace side to insert the string you just matched.

Input: The cat sat, Find: cat, Replace: -$&-, Output: The -cat- sat

Parenthesis () define a capture group. Refer to them in Replace with $1 $2 etc, or in Find with \1 \2 etc.

Input: check the category, Find: (cat)egory, Replace: $1alog, Output: check the catalog

(cat)\1\1 matches catcatcat

Parenthesis beginning with question colon (?:) don't affect $1 or \1 etc. They are useful with quantifiers.

Input: check the category, Find: (?:cat)egory, Replace: $1alog, Output: check the $1alog

cat(?:egory)? matches cat or category

The pipe | matches either what's on its left or what's on its right.

cat|dog|cow matches cat or dog or cow

Quantifiers

Curly braces {} define the minimum and maximum times to match whatever precedes them.

(?:cat){1,2} matches cat or catcat

Omit the second number to allow infinite matches

(?:cat){2,} matches two or more repetitions of cat

Shortcut Quantifiers

?

{0,1}

*

{0,}

+

{1,}

Character Classes

Square brackets [] define a class of matchable characters.

[abc] matches a, b, or c.

Hyphens inside square brackets define ranges.

[a-zA-Z] matches all lower and upper case letters.

A caret ^ at the beginning negates the character class.

[^abc] matches anything but a, b, or c.

Shortcut Character Classes

.

Any Character

\s

White Space

\d

Digit

\w

Letter or Digit

\b

Word Boundary

\n

Newline (enter)

\t

Tab

Escaping

To use a special character literally, precede it with a backslash

5\+5\*2=15\? matches 5+5*2=10?

To use $ in the Replace field, use two $s.

Input: 5 dollars, Find: (\d+) dollars, Replace: $$$1, Output: $5