Perl Programming Language :: Returning substring of regex match


	Returning substring of regex match Hi everyone, Is it possible to ask for a substring, or substrings, of a regular expression match to be returned in a regular expression? EG: Say you want a list of the days in the dates for some input with some defined prefix: eg: Give me the days of all dates that are prefixed with the word DATE DATE22/5/07 1/5/07 DATE25/5/07 DATENO 26/5/07 Would return 22 and 25, but not 1 or 26. Thanks Taras Taras_96 wrote: > Is it possible to ask for a substring, or substrings, of a regular > expression match to be returned in a regular expression? Yes. Use capturing parenteses. -- Gunnar Hjalmarsson Email: http://www.gunnar.cc/cgi-bin/contact.pl On Jun 4, 8:31 am, Taras_96 <taras@gmail.com> wrote: > Say you want a list of the days in the dates for some input > with some defined prefix: > eg: Give me the days of all dates that are prefixed with the > word DATE > DATE22/5/07 > 1/5/07 > DATE25/5/07 > DATENO 26/5/07 > Would return 22 and 25, but not 1 or 26. Is this what you're looking for? #!/usr/bin/perl use strict; use warnings; while (<DATA>) { print "$1\n" if m!DATE(\d+)/\d+/\d+$!; } __DATA__ DATE22/5/07 1/5/07 DATE25/5/07 DATENO 26/5/07 Take a look at perldoc perlretut perldoc perlre perldoc perlreref Paul Lalli Taras_96 wrote: > Is it possible to ask for a substring, or substrings, of a regular > expression match to be returned in a regular expression? > Say you want a list of the days in the dates for some input with some > defined prefix: > eg: Give me the days of all dates that are prefixed with the word DATE > DATE22/5/07 > 1/5/07 > DATE25/5/07 > DATENO 26/5/07 > Would return 22 and 25, but not 1 or 26. You may "literally" put your question into a regular expression, like: ... my @input = qw' DATE22/5/07 1/5/07 DATE25/5/07 DATENO 26/5/07 '; print map /(?<=^DATE)\d+/g, @input; ... The regular expression asks for a numerical value (the day) when encountering the \d+ thing, if it was preceded by the letters DATE, the (?<= ... ) is called "positive lookbehind assertion". The /g modifier in list context (map) extracts the matched expression \d+, (which is the day) - without capturing parentheses. The result of the above expression would then be an "array of the extracted hits (days)", which is printed instantaneously here. Regards M. Mirco Wahab wrote: > ... > my @input = qw' > DATE22/5/07 > 1/5/07 > DATE25/5/07 > DATENO 26/5/07 > '; > print map /(?<=^DATE)\d+/g, @input; > ... The qw() operator puts 'DATENO' and '26/5/07' in two separate elements. -- Gunnar Hjalmarsson Email: http://www.gunnar.cc/cgi-bin/contact.pl Gunnar Hjalmarsson wrote: > Mirco Wahab wrote: >> ... >> my @input = qw' >> DATE22/5/07 >> 1/5/07 >> DATE25/5/07 >> DATENO 26/5/07 <-- !! >> '; >> print map /(?<=^DATE)\d+/g, @input; >> ... > The qw() operator puts 'DATENO' and '26/5/07' in two separate elements. Oh yea, you are right. First, I thought of using _DATA_ but abstained from it because I didn't want to replicate Pauls code parts ... For the OP, the input data needs to be written like: ... my @input = ( 'DATE22/5/07', '1/5/07', 'DATE25/5/07', 'DATENO 26/5/07', ); ... Sorry, M. Mirco Wahab schreef: > the input data needs > to be written like: > ... > my @input = ( > 'DATE22/5/07', > '1/5/07', > 'DATE25/5/07', > 'DATENO 26/5/07', > ); Alternative: my @input = split /\n/, <<'-- '; DATE22/5/07 1/5/07 DATE25/5/07 DATENO 26/5/07 -- Affijn, Ruud "Gewoon is een tijger."