abc

“abc” (the exact character sequence, but anywhere in the string)

^abc

“abc” at the beginning of the string

abc$

“abc” at the end of the string

a|b

Either “a” or “b”

^abc|abc$

The string “abc” at the beginning or at the end of the string

ab{2,4}c

“a” followed by two, three or four “b”s followed by a “c”

ab{2,}c

“a” followed by at least two “b”s followed by a “c”

ab*c

“a” followed by any number (zero or more) of “b”s followed by a “c”

ab+c

“a” followed by one or more b's followed by a c

ab?c

“a” followed by an optional “b” followed by a” c”; that is, either “abc” or ”ac”

a.c

“a” followed by any single character (not newline) followed by a” c “

a\.c

“a.c” exactly

[abc]

Any one of “a”, “b” and “c”

[Aa]bc

Either of “Abc” and “abc”

[abc]+

Any (nonempty) string of “a”s, “b”s and “c”s (such as “a”, “abba”, ”acbabcacaa”)

[^abc]+

Any (nonempty) string which does not contain any of “a”, “b”, and “c” (such as “defg”)

Any two decimal digits, such as 42; same as \d{2}

/i

Makes the pattern case insensitive. For example, /bad language/i blocks any instance of bad language regardless of case.

A “word”: A nonempty sequence of alphanumeric characters and low lines (underscores), such as foo and 12bar8 and foo_1

100\s*mk

The strings “100” and “mk” optionally separated by any amount of white space (spaces, tabs, newlines)

abc\b

“abc” when followed by a word boundary (for example, in “abc!” but not in “abcd”)

perl\B

“perl” when not followed by a word boundary (for example, in “perlert” but not in “perl stuff”)

\x

Tells the regular expression parser to ignore white space that is neither preceded by a backslash character nor within a character class. Use this to break up a regular expression into (slightly) more readable parts.

/x

Used to add regular expressions within other text. If the first character in a pattern is forward slash '/', the '/' is treated as the delimiter. The pattern must contain a second '/'. The pattern between ‘/’ will be taken as a regular expressions, and anything after the second ‘/’ will be parsed as a list of regular expression options ('i', 'x', etc). An error occurs if the second '/' is missing. In regular expressions, the leading and trailing space is treated as part of the regular expression.