in reply to Removing matched pattern except the first pattern

When I first read the OP, the phrase "matched pattern" triggered an "I know, I'll use a regex..." knee-jerk response, and I formulated the problem statement "keep the first n occurrences of a pattern in a string along with any intervening matter and delete all occurrences thereafter".

It turns out that a regex-based approach is not appropriate for the OPed problem unless it be a "keep all lines that match a given regex" strategy, which would, IMHO, be quite good because it combines a possibly quite large element of validation with data extraction and is also completely scaleable.

In any event, proceeding along the lines of my first-but-not-necessarily-best thought, I came up with this, which may be of interest: 

>perl -wMstrict -le
"my $s = 'x foo1 foo2 x foo3 x yfoo9 foo4 foo5 foo9y x foo6 foo7 x';
 print qq{'$s' \n};
 ;;
 my $pat = qr{ \b foo \d \b }xms;
 ;;
 for my $n (0 .. 4) {
   (my $t = $s) =~ s{ \A (?: .*? $pat){$n} \K | $pat }''xmsg;
   print qq{'$t'};
   }
"
'x foo1 foo2 x foo3 x yfoo9 foo4 foo5 foo9y x foo6 foo7 x'

'x   x  x yfoo9   foo9y x   x'
'x foo1  x  x yfoo9   foo9y x   x'
'x foo1 foo2 x  x yfoo9   foo9y x   x'
'x foo1 foo2 x foo3 x yfoo9   foo9y x   x'
'x foo1 foo2 x foo3 x yfoo9 foo4  foo9y x   x'

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Update: I should add that the  \K regex operator used above is available with Perl versions 5.10+.

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Re^2: Removing matched pattern except the first pattern
by rahulruns (Scribe) on May 29, 2013 at 05:28 UTC

    I was able to make the file look like the way I needed but still I am not able to parse the VMstat logs 

    use strict;
use warnings;
use Test::Parser::Vmstat;
use Tie::File;

my @vmstat_data;
tie @vmstat_data, 'Tie::File', $ARGV[0] or die $!;
`sed '/[procs|swpd]/d' $ARGV[0] > /tmp/vmstat_intermidiate`;
open (my $in,  '<',  "/tmp/vmstat_intermidiate") or die "Can't read ol
+d file: $!";
open (my $out, '>', "/tmp/vmstat_log") or die "Can't write new file: $
+!";
print $out "$vmstat_data[0]\n";
print $out "$vmstat_data[1]\n";

while( <$in> )
        {
        print $out $_;
        }

close $out;
close $in;
`rm -rf /tmp/vmstat_intermidiate`;

my $parser = new Test::Parser::Vmstat
    or die "Couldn't create Test::Parser::Vmstat object\n";
my $logfile = '/tmp/vmstat_log';
$parser->parse($logfile)
    or die "Could not parse Vmstat log.\n";

print $parser->to_xml();

OUTPUT
procs -----------memory---------- ---swap-- -----io---- --system-- ---
+--cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us s
+y id wa st
 1  0      0 50122424 234628 9616504    0    0     0    20    2    4  
+0  0 99  0  0
 0  0      0 50121664 234628 9616864    0    0     0     0 7813 5956  
+1  1 98  0  0
 1  0      0 50122252 234628 9616864    0    0     0   190 10727 6872 
+ 2  1 97  0  0
 0  0      0 50122092 234628 9616864    0    0     0   164 8645 6966  
+1  1 98  0  0

PERL SCRIPT OUTPUT

[root@r01mgt ~]# perl parse_vmstat.pl /tmp/vmstat
<vmstat>
</vmstat>

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