Regular Expressions 101

Pro

Character Class[0-9]{8}

{8}matches exactly 8 characters from the set below:

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

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Group 1(abc|def(?=\.pdf))

1st Alternativeabc

abcthe literal text abc (case insensitive)

2nd Alternativedef(?=\.pdf)

defthe literal text def (case insensitive)

Positive Lookahead(?=\.pdf)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

pdfthe literal text pdf (case insensitive)

Non-Capturing Group(?:_xx)?

?repeats the group contents below at most once:

_xxthe literal text _xx (case insensitive)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

pdfthe literal text pdf (case insensitive)

Global pattern flags

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

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

Detailed match information will be displayed here automatically.

26 tokens

[0-9]{8}_(abc|def(?=\.pdf))(?:_xx)?\.pdf

New

20160131_abc.pdf
20160131_abc_xx.pdf
20160131_def.pdf
20160131_def_xx.pdf

20160131_abc.pdf
20160131_abc_xx.pdf
20160131_def.pdf
20160131_def_xx.pdf