Regular Expressions 101

Pro

1st Alternative^[ ]+(*SKIP)(*FAIL) # match spaces at the beginning of a line # these shall fail

^start of line

Character Class[ ]+

+matches at least one character from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

(*SKIP)acts like (*PRUNE), but the next unanchored match attempt starts where (*SKIP) was reached instead of at the next subject character

(*FAIL)forces the current match attempt to fail at this position

Comment: match spaces at the beginning of a line

Comment: these shall fail

2nd Alternative # OR [ ]{2,} # at least two spaces

Comment: OR

Character Class[ ]{2,}

{2,}matches at least 2 characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

Comment: at least two spaces

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

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

^[ ]+(*SKIP)(*FAIL)  # match spaces at the beginning of a line
                     # these shall fail
|                    # OR
[ ]{2,}              # at least two spaces

New

One OS to rule them     all,
    One  OS  to  find    them.
    One     OS to call them    all,
    And  in  salvation    bind         them.
    In  the  bright  land  of  Linux,
    Where the     hackers play.

Extraction

One OS to rule them     all,
    One  OS  to  find    them.
    One     OS to call them    all,
    And  in  salvation    bind         them.
    In  the  bright  land  of  Linux,
    Where the     hackers play.