Re: How to print 5 lines below after a regex match

You test only for matching, but of course what you really want is lines after the match. So while you need to make note that it has matched, you need another indication to tell you when to print. And the indication needs to go away once you've printed the limited number of following lines. '$flag' gets set when we match; '$few' allows us to supply the number of lines, or just allow a default value of 2.

use strict;
my $flag = 0;
my $few = shift || 2;

while (<DATA>) { 
  print $_ if ($flag-- > 0);
  $flag = $few if (/Update certificate/);
}


__DATA__
Useless line before match
Feb 19 15:22:21  206021 152221.684878 7219  INFO: Update certificate f
+or user=(XXX) , updated by XXX
First line after match
Second line after match
Third line after match
Fourth line after match
[download]

Update: output

H:\perl> perl 1156056.pl
First line after match
Second line after match

H:\perl>perl 1156056.pl 3
First line after match
Second line after match
Third line after match
[download]

But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Romans 5:8 (NASB)

Comment on Re: How to print 5 lines below after a regex match Select or Download Code

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Re^2: How to print 5 lines below after a regex match by new2perl2016 (Novice) on Feb 24, 2016 at 20:01 UTC
Thanks I see the lines posted below my match. One last thing which I should have included, how do also print the matched line as well. Many thanks	[reply]
Re^3: How to print 5 lines below after a regex match by poj (Abbot) on Feb 24, 2016 at 20:43 UTC
Set the flag first then print `use strict; my $flag = 0; my $few = shift \|\| 3; while (<DATA>) { $flag = $few if (/Update certificate/); print $_ if ($flag-- > 0); }` [download] poj	[reply] [d/l]
Re^4: How to print 5 lines below after a regex match by Laurent_R (Canon) on Feb 24, 2016 at 21:30 UTC
It really depends on what the OP really needs, but there is a danger of `$flag` being reset while it is reading the next "few" lines, if the regex matches again. Perhaps something like this: `use strict; my $few = shift \|\| 3; while (<DATA>) { if (/Update certificate/) { print $_; print scalar <DATA> for 1..$few; } }` [download] Or possibly `for 1..$few-1;`, depending on whether `$few` includes the matching line or not.	[reply] [d/l] [select]