Regular Expressions 101

Explanation

Pro

1st Alternative(?i)(?<!\S)(<unk>)(?!\S)

(?i)applies the following effective flags to the remainder of the pattern: gmi

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

Negative Lookbehind(?<!\S)

\Sany character that is not Unicode whitespace

Group 1(<unk>)

<unk>the literal text <unk> (case insensitive)

Negative Lookahead(?!\S)

\Sany character that is not Unicode whitespace

2nd Alternative[^\w\s]+

Negated Character Class[^\w\s]+

+matches at least one character outside the set below:

\wa Unicode word character

\sa Unicode whitespace character

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

(?i)(?<!\S)(<unk>)(?!\S)|[^\w\s]+

New

text = "the asbestos fiber <unk> <unk| is < unusually <unk once it enters the <<unk>$% with "
text = "the asbestos fiber <UNK> <unk| is < unusually <unk once it enters the <<unk>$% with "

Substitution

\1

text = "the asbestos fiber <unk> <unk| is < unusually <unk once it enters the <<unk>$% with "
text = "the asbestos fiber <UNK> <unk| is < unusually <unk once it enters the <<unk>$% with "