File open in for loop

kumarboston

Hi All,

How do we open certain number of files in for loop. In my case I have couple of files with name scd_1_2.dat here, the number 1 goes till 5 and 2 goes till 14, I am trying to open recursively but getting some error.

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#!/usr/bin/perl

use strict;

use warnings;
 
for (my $i=1;$i<=5;$i++)

{

    for (my $j=2;$j<=14;$j++)

    {

        open(A, "scd_$i_$j.dat") or die "Check the file";

        open(B,">step$i_$j.out");

        while (<A>)

        {

            my $line = $_; chomp $line;

            my @temp = split (/\s+/,$line);

            my $carbon = $temp[2];

            print B "$carbon\n";

        }

    }

}

The error it gives is:
Global symbol "$i_" requires explicit package name at perl.pl line 12.
Global symbol "$i_" requires explicit package name at perl.pl line 13.
Execution of perl.pl aborted due to compilation errors.

I tried to concatenate the $i and $j using "." but still not able to open file.

Any help will be appreciated.
Thanks
Kumar

nithinpes

First, do not tail to an older thread. You could have created a new thread for this.

The error is shown because the variable $i_ is not defined anywhere! Instead of inserting the variable inbetween string, you should use concatenation(.) operator to concatenate the number to string.

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#!/usr/bin/perl 

use strict; 

use warnings; 
 
for (my $i=1;$i<=5;$i++) 

{ 

    for (my $j=2;$j<=14;$j++) 

    { 

        my $infile= "scd_".$i."_".$j.".dat";

        my $out= "step".$i."_".$j.".out";

        open(A, $infile) or warn "Check the file $infile:$!"; 

        open(B,">$out"); 

        while (<A>) 

        { 

            my $line = $_; chomp $line; 

            my @temp = split (/\s+/,$line); 

            my $carbon = $temp[2]; 

            print B "$carbon\n"; 

        } 

       close A; close B;

    } 

}

Also, make a note that 'warn' is used instead of 'die' because unavailability of any one file would terminate the execution of script otherwise.

KevinADC

You can use curly brackets {} to interpolate scalars inside of double-quoted strings that have other characters in the string that cause perl to see the wrong scalar. Here it is written using perl loops and some other changes:

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#!/usr/bin/perl

use strict;

use warnings;
 
for my $i (1 .. 5){

   for my $j (2 .. 14){

      open(my $IN, "scd_${i}_$j.dat") or warn "Can't open file [scd_${i}_$j.dat]: $!\n";

      open(my $OUT, ">", "step${i}_$j.out") or warn "Can't open file [step${i}_$j.out]: $!\n";

      while (<$IN>){

         print $OUT (split(/\s+/))[2],"\n";

      }

   }

}

And as nithinpes mentioned, next time start a new thread when you have a new question.

File open in for loop

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