Perl: Match pattern and print next N lines K times

Question

Perl: Match pattern and print next N lines K times

I have a text file similar to this

count="4"
data1
data2
data3
Data1
Data2
Data3

I need to find a string count

and take its value (4) and print the next 3 lines (4) times.

The output in the file should be

data1
data2
data3
data1
data2
data3
data1
data2
data3
data1
data2
data3
Data1
Data2
Data3

I have tried this Perl code

while ( <FILE> ) {
    $n = 3
    if ( $_ =~ /count="4"/ ) {
        print FILE if ($n-- > 0) x 4;
    }

But it doesn't work.

+3

regex perl

SK 11 jul. 15 at 13:10

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4 answers

user52889 · Answer 1 · 2015-07-11T13:48:56+0000

But it doesn't work.

It's because

if ($n-- > 0) x 4

doesn't do what you want. x

repeats the value (i.e. you do if 1111

), it doesn't repeat the statement.

Try:

use strict; use warnings;
while (<FILE>) {
  if ( /count="(\d+)"/ ) {
    for ( 1..$1 ) {
      if ( defined ( my $l = <FILE> ) ) {
        print $l;
      }
    }
  }
}

This will help you get started.

In the future, please note:

Instead of "not working". Give the actual result (even if all you can say is "prints nothing and throws no errors")
When something doesn't work, consider the perl debugger
Notice use strict;

and use warnings;

- this will help you avoid mistakes .
Learn about capturing perlre and $ 1 and other regex related perlvar variables

stevieb · Answer 2 · 2015-07-11T14:19:00+0000

You can try something like this:

#!/usr/bin/perl
use strict;
use warnings;

my $count = 0;

while (my $line = <DATA>){
    if ($line =~ /count="(\d+)"/ and $1){
        $count = $1;
        next;
    }
    if ($count){
        print $line;
        $count--;
    }
}
__DATA__
count="2"
a
b
c
d
count="1":
e
f
g
count="3"
h
i
j
k
l

Sant · Answer 3 · 2015-07-12T07:34:45+0000

you can point the file / input to @data

#!/usr/bin/perl 
use strict;
use warnings;
my @data = qw /count="4" data1-1 data2-1 data3-1 Data1 Data2 Data3/;
my $repeat_line = 3;
foreach (@data)
{
  if ( /count="(\d+)"/ ) {
    for ( 1..$1 ) {
      for my $no1 ( 1..$repeat_line ) {
    print $data[$no1],"\n";
      }
    }
  }
}
for my $no ($repeat_line..scalar(@data)) {
  if(defined $data[$no+1]){
    print $data[$no+1],"\n";
  }
}

Output

data1-1
data2-1
data3-1
data1-1
data2-1
data3-1
data1-1
data2-1
data3-1
data1-1
data2-1
data3-1
Data1
Data2
Data3

Casimir et Hippolyte · Answer 4 · 2016-05-20T02:56:02+0000

You can use this one liner:

perl -ne 'print m/count="(\d+)"/?$n=(<>.<>.<>)x$1:$_' file
#         ^     ^                ^            ^  ^^---- the current line.
#         |     |                |            |  '---- else
#         |     |                |            '---- repeated $1 times
#         |     |                '---- the three next lines (if any) stored in $n
#         |     '---- when this pattern succeeds,
#         '---- Print,

Perl: Match pattern and print next N lines K times

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