Find multiline blocks - regex

Question

I'm trying to find occurrences of BLOB_SMUGHO, from the file test.out from the bottom of the file. If found, return a chunk of data which I'm interested in between the string "2014.10"
I'm getting Use of uninitialized value $cc in pattern match (m//) at
Whats is wrong with this script?
#!/usr/bin/perl
use strict;
use warnings;
use POSIX qw(strftime);
use File::ReadBackwards;
my $find = "BLOB_SMUGHO";
my $chnkdelim = "\n[" . strftime "%Y.%m", localtime;
my $fh = File::ReadBackwards->new('test.out', $chnkdelim, 0) or die "err-file: $!\n";
while ( defined(my $line = $fh->readline) ) {
if(my $cc =~ /$find/){
print $cc;
}
}
close($fh);
In case if this helps, here is a sample content of test.out
2014.10.31 lots and
lots of
gibbrish
2014.10.31 which I'm not
interested
in. It
also
2014.10.31 spans
across thousands of
lines and somewhere in the middle there will be
2014.10.31
this precious word BLOB_SMUGHO and
2014.10.31 certain other
2014.10.31 words
2014.10.31
this precious word BLOB_SMUGHO and
2014.10.31
this precious word BLOB_SMUGHO and
which
I
will
be
interested
in.
And I'm expecting to capture all the multiple occurrences of the chunk of the text from bottom of the file.
2014.10.31
this precious word BLOB_SMUGHO and

Answer 1

First, you have written your match incorrectly due to misunderstanding the =~ operator:
if(my $cc =~ /$find/){ # incorrect, like saying if(undef matches something)
If you want to match what is in $line against the pattern between /.../ then do:
if($line =~ /$find/) {
The match operator expects a value on left side as well as right side. you were using it like an assignment operator.
If you need to capture the match(es) into a variable or list, then add it to the left of an equal sign:
if(my ($cc) = $line =~ /$find/) { <-- wrap $cc in () for list context
By the way, I think you are better off writing:
if($line =~ /$find/) {
print $line;
or if you want to print what you matched only
print $0;
Since you aren't capturing a substring, it doesnt really matter here.
Now, as to how to match everything between two patterns, the task is easier if you don't match line by line, but match across newlines using the /s modifier.
In Perl, you can set the record separator to undef and use slurp mode.
local $/ = undef;
my $s = <>; # read all lines into $s
Now to scan $s for patterns
while($s =~ /(START.*?STOP)/gsm) { print "$1\n"; } # print the pattern inclusive of START and STOP
Or to capture between START and STOP
while($s =~ /START(.*?)STOP/gsm) { print "$1\n"; } # print the pattern between of START and STOP
So in your case the start pattern is 2014.10.31 and stop is BLOB_SMUGHO
while($s =~ /(2014\.10\.31.*?BLOB_SMUGHO)/gsm) {
print "$1\n";
}
NOTE: Regex modifiers in Perl come after the last / so if you see I use /gsm for multiline, match newline, and global matching (get multiple matches in a loop by remembering the last location).