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Regex

3.9.1 The Match-beginning-of-line Operator (^)

This operator can match the empty string either at the beginning of the string or after a newline character. Thus, it is said to anchor the pattern to the beginning of a line.

In the cases following, `^' represents this operator. (Otherwise, `^' is ordinary.)

• It (the `^') is first in the pattern, as in `^foo'.

• The syntax bit RE_CONTEXT_INDEP_ANCHORS is set, and it is outside a bracket expression.

• It follows an open-group or alternation operator, as in `a\(^b\)' and `a\|^b'. See section 3.7 Grouping Operators (( ... ) or \( ... \)), and 3.5 The Alternation Operator (| or \|).

These rules imply that some valid patterns containing `^' cannot be matched; for example, `foo^bar' if RE_CONTEXT_INDEP_ANCHORS is set.

If the not_bol field is set in the pattern buffer (see section 7.1.1 GNU Pattern Buffers), then `^' fails to match at the beginning of the string. See section 7.2.3 POSIX Matching, for when you might find this useful.

If the newline_anchor field is set in the pattern buffer, then `^' fails to match after a newline. This is useful when you do not regard the string to be matched as broken into lines.