PERL: extract lines between two patterns

Shell Programming and Scripting
1

Hello Perl-experts,

I am new to perl and need help to solve a problem.

I have a table in below format.
<Text A>
<Pattern1>
A Value
B Value
C Value
D Value
<Pattern2>
<Text B>

This table is in file1. I want to extract lines between Pattern1 and Pattern2 and write it into file2. Please provide me some help to do this. Thanks

2

can you please write the real environment example

3

Thanks for your reply.

please find the actual code below.

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

our $fh;
our $log;

open($fh,">","block.power");
open ($log,">","temp.log") or die "can not open file $log : $!\n" ;
while($fh){
   if (/Total Design Power Summary \(Worst/ ... /\|Total/)
  {printf $log;}
}

I'm getting below message when i run this script.

Use of uninitialized value in pattern match (m//) at temp.pl line 11.
4

if (/Total Design Power Summary \(Worst/ ... /\|Total/)
whats this

5

See if this helps...

perl -ne ' if(/<Pattern2>/){$p=0} if(/<Pattern1>/){$p=1;next}print if$p' infile > outfile

--ahamed

6 
#!/usr/bin/perl -w
use strict;
use warnings;

print "enter the first pattern-:\n";
my $pat1=<>;
print "enter the second pattern-:\n";
my $pat2=<>;
my $en1=0;
my $en2=0;
open FILE, "<file1.txt" or die $!;
#my @lines=<FILE>;
my $i =0;
while(<FILE>)
{
	$i++;
if( $_ eq $pat1)
{	$en1=$i;
}
if( $_ eq $pat2)
{	 $en2=$i;
}
}
close(FILE);

open FILE, "<file1.txt" or die $!;
my @lines=<FILE>;

for(my $j=$en1; $j<($en2-1); $j++)
{
	print $lines[$j];
}
close(FILE);

check this if it helps you and please manipulate as per your requirment

---------- Post updated at 12:45 PM ---------- Previous update was at 12:45 PM ----------

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

print "enter the first pattern-:\n";
my $pat1=<>;
print "enter the second pattern-:\n";
my $pat2=<>;
my $en1=0;
my $en2=0;
open FILE, "<file1.txt" or die $!;
#my @lines=<FILE>;
my $i =0;
while(<FILE>)
{
	$i++;
if( $_ eq $pat1)
{	$en1=$i;
}
if( $_ eq $pat2)
{	 $en2=$i;
}
}
close(FILE);

open FILE, "<file1.txt" or die $!;
my @lines=<FILE>;

for(my $j=$en1; $j<($en2-1); $j++)
{
	print $lines[$j];
}
close(FILE);

chech this if it helps you and please manipulate as per your requirment

7

With possible corrections.

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

our $fh;
our $log;

open($fh,"<","block.power"); # Here the arrow should point towards left to imply you're reading from file.
open ($log,">>","temp.log") or die "can not open file $log : $!\n" ; # Use >> to append. You don't want the log file to contain only the last printed line, do you?
while($fh){
   if (/Total Design Power Summary \(Worst/../\|Total/)
  {printf $log;}
}
close $log; #Though your file handles would close upon exit, 
close $fh; # its always a good practice to close them yourself.
8

hi balajesuri..
Nice Script....
Can you please explain me the lineif (/Total Design Power Summary \(Worst/../\|Total/).

I didn't get it clearly. Thanks in advance.
I learn from you very much.

9

if-condition is true if current line in buffer is in between the two patterns

10

thats true. but i want to know how does it execute
/Total Design Power Summary \(Worst/../\|Total/

11

Thanks to all of you for your help. Now I'm able to get my code work.
Posting it below.

#!/usr/bin/perl 
#use strict; 
#use warnings; 
my $fh; 
my $log; 
my $line;
open($fh,"<","file1") or die "can not open file $fh : $!\n" ; 
open ($log,">","file2")or die "can not open file $log : $!\n" ; 
while($line = <$fh>)
{
   if ($line =~ /pattern1/ ) 
   {  
	  printf $log $line;
	  while($line = <$fh>) 
	  {
		 if($line =~ /pattern2/)
		 {
			printf $log $line;  
			last;
		 } else
		 {
			printf $log $line;  
		 }  
     }
     }
   } 
close $fh;
close $log;

Happy to take your advice to make this code more efficient.

12

@mnithink: Not sure how your code worked! It doesn't work for me. Try this: (and please use code tags)

#!/usr/bin/perl
use strict; # Its a good practice not to comment these two pragmas.
use warnings;

open I, "< file1";
open O, "> file2";

foreach (<I>) {
    if (/Pattern1/ .. /Pattern2/) { print O }
}

close O;
close I;

@parthmittal2007: (/Pattern1/../Pattern2/) is known as flip-flop operator in perl. Imagine this: While reading a file line by line, perl sets an internal flag to true the moment it encounters 'Pattern1' and the if-block is executed until it encounters 'Pattern2' in a line (when it sees Pattern2, it sets the same internal flag to false). Thus, for lines before Pattern1 or after Pattern2 the flag would be false, thereby failing the if-condition.

For e.g.:

foreach (<I>) {
    if (/Pattern1/ .. /Pattern2/) { print O }
}

This would print all the lines in between (and inclusive of) 'Pattern1' and 'Pattern2' into the out file-handle.

1 Like