How can I extract a substring up to the first digit?

Question

How can I find the first substring until I find the first digit?

Example:

my $string = \'AAAA_BBBB_12_13_14\' ;

Result expected: \'AAA

Answer 1

Most people got half of the answer right, but they missed several key points.

• You can only trust the match variables after a successful match. Don't use them unless you know you had a successful match.

• The $&, $``, and$'` have well known performance penalties across all regexes in your program.

• You need to anchor the match to the beginning of the string. Since Perl now has user-settable default match flags, you want to stay away from the ^ beginning of line anchor. The \A beginning of string anchor won't change what it does even with default flags.

This would work:

my $substring = $string =~ m/\A(\D+)/ ? $1 : undef;

If you really wanted to use something like $&, use Perl 5.10's per-match version instead. The /p switch provides non-global-perfomance-sucking versions:

my $substring = $string =~ m/\A\D+/p ? ${^MATCH} : undef;

If you're worried about what might be in \D, you can specify the character class yourself instead of using the shortcut:

my $substring = $string =~ m/\A[^0-9]+/p ? ${^MATCH} : undef;

I don't particularly like the conditional operator here, so I would probably use the match in list context:

my( $substring ) = $string =~ m/\A([^0-9]+)/;

If there must be a number in the string (so, you don't match an entire string that has no digits, you can throw in a lookahead, which won't be part of the capture:

my( $substring ) = $string =~ m/\A([^0-9]+)(?=[0-9])/;