topic Re: PERL - pattern match in Operating System - Linux

PERL - pattern match

Pat Tom — Tue, 13 Feb 2007 16:57:31 GMT

I am writing a PERL script that would search for a pattern in a file. Once the pattern is found, the script should store the portion of the file from the pattern till the end of the file in a buffer for further processing.

I am somehow not able to get the logic.

Can anyone please help.

Thanks,
Pat

Re: PERL - pattern match

James R. Ferguson — Tue, 13 Feb 2007 17:58:05 GMT

Hi Pat:

OK, this script meets your requirement. Once a pattern is found, the remainder of a line is stored and every line in the file thereafter. You can do what you wish with the array --- I printed what I stored (buffered) to show the technique.

# cat ./buffer
#!/usr/bin/perl
use strict;
use warnings;
my $pattern = shift;
my $ok;
my @lines;
while (<>) {
chomp;
if (/($pattern)(.*)/) {
push( @lines, $2 );
$ok++;
}
push( @lines, $_ ) if $ok;
}
print "$_\n" for (@lines)

...run as:

# ./buffer local /etc/hosts

...that is, pass the pattern to match followed by the file to be processed.

Regards!

...JRF...

Re: PERL - pattern match

James R. Ferguson — Tue, 13 Feb 2007 17:58:15 GMT

Re: PERL - pattern match

Hein van den Heuvel — Tue, 13 Feb 2007 18:11:27 GMT

Pat,

JRF has the 'de luxe' solution.
If you study it, you'll see it raises (and answer) some questions:

'from the pattern' is that to be taken literally? That is, should it included the pattern itself, or perhaps even the whole 'line' which contained the pattern?

'till the end': What to do with new-lines?

probably not what you need, but here is a one line for the simplest interpretation of the request...

perl -ne '$go++ if /pattern/; print if $go' >

Hein.

Re: PERL - pattern match

James R. Ferguson — Wed, 14 Feb 2007 08:19:07 GMT

Hi (again) Pat:

Sorry for the double post. The Forum returned an error in posting the first time --- I should know better.

There is a dumb correction, anyway I need to make! The original solution dropped a 'next' and treated multiple instances of the pattern downstream from the first occurance as reason to chop the beginning of the line again. That's probably not desirable. Hence, use this:

#!/usr/bin/perl
use strict;
use warnings;
my $pattern = shift;
my $ok;
my @lines;
while (<>) {
chomp;
if ( /($pattern)(.*)/ && ! $ok ) {
push( @lines, $2 );
$ok++;
next;
}
push( @lines, $_ ) if $ok;
}
print "$_\n" for (@lines);

Note, however, that you will *miss* the line which *ends* with the pattern sought. According to your specifications, you only want "...from the pattern until the end...". Perhaps you can clarify what behavior you want.

Regards!

...JRF...

Re: PERL - pattern match

H.Merijn Brand (procura — Wed, 14 Feb 2007 08:23:18 GMT

# perl -ne'1../pattern/ or print' file > part

Explain what is wrong with that?

Enjoy, Have FUN! H.Merijn

Re: PERL - pattern match

Peter Nikitka — Thu, 15 Feb 2007 03:33:09 GMT

Hi Merijn,

your oneliner will not output the line with the first match :-)

mfG Peter