Regular Expressions 101

Pro

Non-Capturing Group(?:X-)?

?repeats the group contents below at most once:

X-the literal text X- (case sensitive)

Received: the literal text Received: (case sensitive)

Non-Capturing Group(?:by|from)

1st Alternativeby

bythe literal text by (case sensitive)

2nd Alternativefrom

fromthe literal text from (case sensitive)

the literal (32₁₀ / 40₈ / 20₁₆)

\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match

Group 1([\S]+)

Character Class[\S]+

+matches at least one character from the set below:

\Sany non-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

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

(?:X-)?Received: (?:by|from) \K([\S]+)

New

Received: from mail2.oknotify2.com (mail2.oknotify2.com. [208.83.243.70]) by mx.google.com with ESMTP id dp5si2596299pdb.170.2015.06.03.14.12.03

Received: by 10.66.156.198 with SMTP id wg6mr62843415pab.126.1433365924352;

Received: from localhost (localhost [127.0.0.1])