Regular Expressions

Regular expressions is a formal language that is used to find strings or parts of strings that match a specific pattern.

Examples of regular expressions that are useful in the context of Mp3tag are collected at the Regular Expressions topic of the Mp3tag Community Forums.

The following provides a short introduction to the syntax of regular expressions in Mp3tag.

Literals

All characters except .|*?+(){}[]^$. These characters are literals when preceded by a \.

Wildcard

The dot character . matches any single character.

Repeats


`*`	repeated any number of times including zero
`+`	repeated any number of times, but at least once
`?`	repeated zero or one times only
`a{n}`	represents the letter `a` repeated exactly `n` times
`a{n,}`	represents the letter `a` repeated at least `n` times with no upper limit
`a{n,m}`	represents the letter `a` repeated between `n` and `m` times

Non-greedy repeats

A non-greedy repeat is one which will match the shortest possible string. Non-greedy repeats are possible by appending a ? after the repeat.

Parenthesis

Parentheses serve two purposes,

to group items together into a subexpression, and
to mark what generated the match. $N Expands to the text that matched sub-expression N in Replace matches with.

Alternatives

Alternatives occur when the expression can match either one sub-expression or another, each alternative is separated by a |.

Line anchors


`^`	matches the start of a line
`$`	matches the end of a line

Sets


`[abc]`	matches either of `a`, `b`, or `c`
`[^abc]`	matches any character other than `a`, `b`, or `c`
`[a-z]`	matches any character in the range `a` to `z`
`[^A-Z]`	matches any character other than those in the range `A` to `Z`
`\w`	matches any word character - all alphanumeric characters plus the underscore
`\s`	matches any whitespace character
`\d`	matches any digit (0-9)
`\l`	matches any lower case character
`\u`	matches any upper case character
`\W`	matches any non-word character
`\S`	matches any non-whitespace character
`\D`	matches any non-digit character
`\L`	matches any non-lower case character
`\U`	matches any non-upper case character
`\t`	matches the tab character
`\n`	matches the newline character
`\r`	matches the carriage return character
`\r\n`	matches a Windows style line break
`\xnn`	matches a character with Unicode hex value `nn`
`\x{nnnn}`	matches a character with Unicode hex value `nnnn`

Word boundaries


`\b`	matches a word boundary (the start or end of a word)
`\B`	matches only when not at a word boundary

Mp3tag uses the Boost.Regex expression engine which has a Perl regular expression syntax. The Boost-Extended Format String Syntax is not enabled in Mp3tag.