Regular Expressions Anchor Characters: Caret (^) Multiline modifier
Example
By default, the caret ^ metacharacter matches the position before the first
character in the string.
Given the string "charsequence" applied
against the following patterns: /^char/ & /^sequence/, the engine will try to match as follows:
-
/^char/- ^ -
charsequence - c -
charsequence - h -
charsequence - a -
charsequence - r -
charsequence
Match Found
- ^ -
-
/^sequence/- ^ -
charsequence - s -
charsequence
Match not Found
- ^ -
The same behaviour will be applied even if the string contains line terminators, such as \r?\n. Only the position at the start of the string will be matched.
For example:
/^/g
┊char\r\n
\r\n
sequence
However, if you need to match after every line terminator, you will have to set the multiline mode (//m, (?m)) within your pattern. By doing so, the caret ^ will match "the beginning of each line", which corresponds to the position at the beginning of the string and the positions immediately after1 the line terminators.
1 In some flavors (Java, PCRE, ...), ^ will not match after the line terminator, if the line terminator is the last in the string.
For example:
/^/gm
┊char\r\n
┊\r\n
┊sequence
Some of the regular expression engines that support Multiline modifier:
-
Pattern pattern = Pattern.compile("(?m)^abc"); Pattern pattern = Pattern.compile("^abc", Pattern.MULTILINE); -
var abcRegex = new Regex("(?m)^abc"); var abdRegex = new Regex("^abc", RegexOptions.Multiline) -
/(?m)^abc/ /^abc/m -
Python 2 & 3 (built-in
remodule)abc_regex = re.compile("(?m)^abc"); abc_regex = re.compile("^abc", re.MULTILINE);
