regex101: PCRE (Legacy) Match Workspace

^start of line

Character Class[a-zA-Z0-9_]{1}

{1}matches one character from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

0-9one character from 0 (48₁₀) to 9 (57₁₀)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Group 1(([a-zA-Z0-9_]|\.)*[a-zA-Z0-9_]{1})?

?repeats the group contents below at most once:

Group 2([a-zA-Z0-9_]|\.)*

*repeats the group contents below any number of times:

1st Alternative[a-zA-Z0-9_]

Character Class[a-zA-Z0-9_]

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

0-9one character from 0 (48₁₀) to 9 (57₁₀)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

2nd Alternative\.

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[a-zA-Z0-9_]{1}

{1}matches one character from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

0-9one character from 0 (48₁₀) to 9 (57₁₀)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

$end of line

the literal ↵ (10₁₀ / 12₈ / A₁₆)

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Search reference

Regular Expression

^[a-zA-Z0-9_]{1}(([a-zA-Z0-9_]|\.)*[a-zA-Z0-9_]{1})?$

New

# valid names
_123
_123.123
_123.abc
_abc.123
_abc.abc
_valid
_Valid
_valid123
1
1.1
123
a
a____a
a___a
a__a
a.a
A.A
Valid
valid_
valid_name
valid.name
valid123
validname
# invalid names
_
__
___
____
_.
.
._
.1
.123
.a
.A
.no_starting_period
1.
a.
A.
invalid name
invalid-name
invalid,name
invalid;name
invalid:name
invalid!name
invalid?name
invalid'name
invalid"name
invalid(name
invalid)name
invalid@name
invalid/name
invalid\name
invalid&name
invalid#name
invalid%name
invalid`name
invalid^name
invalid^name
invalid+name
invalid<name
invalid=name
invalid>name
invalid|name
invalid~name
invalid$name
no_ending_period.