Regular Expressions For Regular Folk

Character Escapes

Character escapes act as shorthands for some common character classes.

Digit character — `\d`

The character escape \d matches digit characters, from 0 to 9. It is equivalent to the character class [0-9].

/\d/g[RegExr] [Visual]

4 matches2020
1. 2
2. 0
3. 2
4. 0
6 matches100/100
1. 1
2. 0
3. 0
4. 1
5. 0
6. 0
3 matchesIt costs $5.45
1. 5
2. 4
3. 5
6 matches3.14159
1. 3
2. 1
3. 4
4. 1
5. 5
6. 9

/\d\d/g[RegExr] [Visual]

2 matches2020
1. 20
2. 20
2 matches100/100
1. 10
2. 10
1 matchIt costs $5.45
1. 45
2 matches3.14159
1. 14
2. 15

\D is the negation of \d and is equivalent to [^0-9].

/\D/g[RegExr] [Visual]

0 matches2020
1 match100/100
1. /
11 matchesIt costs $5.45
1. I
2. t
4. c
5. o
6. s
7. t
8. s
10. $
11. .
1 match3.14159
1. .

Word character — `\w`

The escape \w matches characters deemed “word characters”. These include:

lowercase alphabet — a–z
uppercase alphabet — A–Z
digits — 0–9
underscore — _

It is thus equivalent to the character class [a-zA-Z0-9_].

/\w/g[RegExr] [Visual]

6 matchesjohn_s
1. j
2. o
3. h
4. n
5. _
6. s
7 matchesmatej29
1. m
2. a
3. t
4. e
5. j
6. 2
7. 9
6 matchesAyesha?!
1. A
2. y
3. e
4. s
5. h
6. a
4 matches4952
1. 4
2. 9
3. 5
4. 2
4 matchesLOUD
1. L
2. O
3. U
4. D
4 matcheslo-fi
1. l
2. o
3. f
4. i
6 matchesget out
1. g
2. e
3. t
4. o
5. u
6. t
6 matches21*2 = 42(1)
1. 2
2. 1
3. 2
4. 4
5. 2
6. 1

/\W/g[RegExr] [Visual]

0 matchesjohn_s
2 matchesAyesha?!
1. ?
2. !
0 matches4952
0 matchesLOUD
1 matchlo-fi
1. -
1 matchget out
3 matches;-;
1. ;
2. -
3. ;
6 matches21*2 = 42(1)
1. *
3. =
5. (
6. )

Whitespace character — `\s`

The escape \s matches whitespace characters. The exact set of characters matched is dependent on the regex engine, but most include at least:

space
tab — \t
carriage return — \r
new line — \n
form feed — \f

Many also include vertical tabs (\v). Unicode-aware engines usually match all characters in the separator category.

The technicalities, however, will usually not be important.

/\s/g[RegExr] [Visual]

1 matchword word
2 matchestabs vs spaces
0 matchessnake_case.jpg

/\S/g[RegExr] [Visual]

8 matchesword word
1. w
2. o
3. r
4. d
5. w
6. o
7. r
8. d
12 matchestabs vs spaces
1. t
2. a
3. b
4. s
5. v
6. s
7. s
8. p
9. a
10. c
11. e
12. s
14 matchessnake_case.jpg
1. s
2. n
3. a
4. k
5. e
6. _
7. c
8. a
9. s
10. e
11. .
12. j
13. p
14. g

Any character — `.`

While not a typical character escape, . matches any¹ character.

/./g[RegExr] [Visual]

6 matchesjohn_s
1. j
2. o
3. h
4. n
5. _
6. s
8 matchesAyesha?!
1. A
2. y
3. e
4. s
5. h
6. a
7. ?
8. !
4 matches4952
1. 4
2. 9
3. 5
4. 2
4 matchesLOUD
1. L
2. O
3. U
4. D
5 matcheslo-fi
1. l
2. o
3. -
4. f
5. i
7 matchesget out
1. g
2. e
3. t
5. o
6. u
7. t
3 matches;-;
1. ;
2. -
3. ;
12 matches21*2 = 42(1)
1. 2
2. 1
3. *
4. 2
6. =
8. 4
9. 2
10. (
11. 1
12. )

Except the newline character \n. This can be changed using the “dotAll” flag, if supported by the regex engine in question.↩