Regular Expressions 101

^start of line

Group 1(.*?)?

?repeats the group contents below at most once:

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

&?optionally matches the literal & (38₁₀ / 46₈ / 26₁₆)

tag=the literal text tag= (case insensitive)

Negated Character Class[^&]*?

*?matches any number of characters outside the set below:

&the literal & (38₁₀ / 46₈ / 26₁₆)

Group 2(&.*)?

?repeats the group contents below at most once:

&the literal & (38₁₀ / 46₈ / 26₁₆)

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

$end of line

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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

^(.*?)?&?tag=[^&]*?(&.*)?$

Test String
New

# Match
test=dsfsdfsdfdsfsdltag&tag=sdfdsfsdfdsfds&blah=sdfdsfdsfds&fsdfsdfsdf
fillHeight=191&fillWidth=340&quality=96&tag=736d0dfc2ad7fc74d1f8a6a655b540ae
test=dsfsdfsdfdsfsdltag&tag=sdfdsfsdfdsfds

# No match
test=dsfsdfsdfdsfsdltag&blah=sdfdsfdsfdstag

Regular Expression

Test StringNew

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Test String
New

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