CODEWITHSUNDEEP
regexperl
Jorge
Jorge

Reputation: 695

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

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

Example:

my $string = 'AAAA_BBBB_12_13_14' ;

Result expected: 'AAAA_BBBB_'

Upvotes: 3

Views: 10162

Answers (4)

brian d foy
brian d foy

Reputation: 132858

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])/;

Upvotes: 2

David Webb
David Webb

Reputation: 193714

Judging from the tags you want to use a regular expression. So let's build this up.

This gives us the following regular expression:

^\D+

Which we can use in code like so:

my $string = 'AAAA_BBBB_12_13_14';
$string =~ /^\D+/;
my $result = $&;

Upvotes: 7

JRFerguson
JRFerguson

Reputation: 7526

perl -le '$string=q(AAAA_BBBB_12_13_14);$string=~m{(\D+)} and print $1'
AAAA_BBBB_

Upvotes: 0

gaussblurinc
gaussblurinc

Reputation: 3692

  $str =~ /(\d)/; print $`;

This code print string, which stand before matching

Upvotes: 0

Related Questions