Regular Expressions 101

Explanation

Pro

^start of line

Negated Character Class[^0-9\n]*

*matches any number of characters outside the set below:

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

\na line-feed (newline) character (ASCII 10)

Non-Capturing Group(?:((?|[12](?=(?>.*\n)*([^#]+))|3(?=(?>.*\n)*[^#]*#([^#]+))|[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+)))\d+).*|.*\z)

1st Alternative((?|[12](?=(?>.*\n)*([^#]+))|3(?=(?>.*\n)*[^#]*#([^#]+))|[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+)))\d+).*

Group 1((?|[12](?=(?>.*\n)*([^#]+))|3(?=(?>.*\n)*[^#]*#([^#]+))|[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+)))\d+)

Branch Reset Group(?|[12](?=(?>.*\n)*([^#]+))|3(?=(?>.*\n)*[^#]*#([^#]+))|[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+)))

1st Alternative[12](?=(?>.*\n)*([^#]+))

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Positive Lookahead(?=(?>.*\n)*([^#]+))

Atomic Group(?>.*\n)*

*repeats the group contents below any number of times:

.*any character (except for line terminators), repeated any number of times

\na line-feed (newline) character (ASCII 10)

Group 2([^#]+)

Negated Character Class[^#]+

+matches at least one character outside the set below:

#the literal # (35₁₀ / 43₈ / 23₁₆)

2nd Alternative3(?=(?>.*\n)*[^#]*#([^#]+))

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Positive Lookahead(?=(?>.*\n)*[^#]*#([^#]+))

Atomic Group(?>.*\n)*

*repeats the group contents below any number of times:

.*any character (except for line terminators), repeated any number of times

\na line-feed (newline) character (ASCII 10)

Negated Character Class[^#]*

*matches any number of characters outside the set below:

#the literal # (35₁₀ / 43₈ / 23₁₆)

Group 2([^#]+)

Negated Character Class[^#]+

+matches at least one character outside the set below:

#the literal # (35₁₀ / 43₈ / 23₁₆)

3rd Alternative[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+))

Character Class[45]

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

Positive Lookahead(?=(?>.*\n)*(?:[^#]*#){2}([^#]+))

Atomic Group(?>.*\n)*

*repeats the group contents below any number of times:

.*any character (except for line terminators), repeated any number of times

\na line-feed (newline) character (ASCII 10)

Non-Capturing Group(?:[^#]*#){2}

{2}repeats the group contents below exactly 2 times:

Negated Character Class[^#]*

*matches any number of characters outside the set below:

#the literal # (35₁₀ / 43₈ / 23₁₆)

Group 2([^#]+)

Negated Character Class[^#]+

+matches at least one character outside the set below:

#the literal # (35₁₀ / 43₈ / 23₁₆)

\d+a digit, repeated at least once

.*any character (except for line terminators), repeated any number of times

2nd Alternative.*\z

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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

^[^0-9\n]*(?:((?|[12](?=(?>.*\n)*([^#]+))|3(?=(?>.*\n)*[^#]*#([^#]+))|[45](?=(?>.*\n)*(?:[^#]*#){2}([^#]+)))\d+).*|.*\z)

New

Blah 12345 Blah
Blah 22345 Blah
Blah 32345 Blah
Blah 42345 Blah
Blah 52345 Blah
AAA#BBB#XYZ

Substitution

$2$1

Blah 12345 Blah
Blah 22345 Blah
Blah 32345 Blah
Blah 42345 Blah
Blah 52345 Blah
AAA#BBB#XYZ