Reading and writing simultaneously to a file

[hbkid]

I'm trying to read and write to a file at the same time.
I used open ( FILE, +<$file_name) to make $file_name both readable and writeable.
I basically want to replace
x
y
z

in the file
with
x
a
y
z

When I tried doing this with an algorithm that works like this

if $line = /x/
print FILE a;
This did not work
How do I do this?.
Thanks in advance,

 

[KevinADC]

thats not an algorithm, nor is it a regexp, its an assingment operator (=) which is not what you want to do. This is probably what you want to do:

while (<FILE>) {
   print FILE "x\na\n" if (/x/);
}

or more like you were trying:

while (<FILE>) {
   $line = $_;   
   if ($line [b]=~[/b] /x/) {
      print FILE "x\n";
      print FILE "a\n";
   }
}

although I am not sure how well supported the "+<" operator is.

 

[rharsh]

Is there a reason you couldn't use a temp file? I didn't test the code, but something like:

open IN, "< $file_name" or die;
open OUT, "> ${file_name}.tmp" or die;

while ($line = <IN>) {
    print OUT $line;
    if ($line =~ /x/) {
        print OUT "a\n";
    }
}
close IN;
close OUT;

unlink($file_name);
rename("${file_name}.tmp", $file_name);

 

[TonyGroves]

When you write to a file in that way, you are overwriting the current contents, not inserting.

You would be better off either making a copy of the file, then reading in the copy and writing to the original, or reading the entire file into an array and writing out the new version.

 

[KevinADC]

won't this overwrite the line with x in it instead of insert a after x?

while ($line = <IN>) {
    print OUT $line;
    if ($line =~ /x/) {
        print OUT "a\n";
    }
}

 

[hbkid]

Sorry, I may have over simplified the problem..
What I do have is a hash and I need to install the 2 values in the hash after line x depending on the if condition below. The code I have so far.


open (OUT, "+<$out_file") || die "Cannot open output.txt";
while (defined ($line = <OUT>)) {
foreach $key (sort keys %cell_port_hash) {
@key_array = split ('_', $key);
$key1 = $key_array[0];
if (defined $key1) {
if ($line =~ /$key1/) {
if ($cell_port_hash{$key} !~ /O/) {
print OUT "\(\"$cell_port_hash{$key}\" \"Input\" \)\n";
} else {
print OUT "\(\"$cell_port_hash{$key}\" \"Output\" \)\n";
}
}
}
}
}

 

[rharsh]

KevinADC, I decided to test the code since there was some uncertainty.

while ($line = <DATA>) {
    print $line;
    if ($line =~ /x/) {
        print "a\n";
    }
}

__DATA__
x
y
z

Output:

x
a
y
z

 

[ishnid]

I like to use Tie::File for problems like this:

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

use Tie::File;

tie my @file_array, 'Tie::File', 'test.dat';

my $i = 0;
while ( $i < @file_array ) {
   if ( $file_array[ $i ] =~ /x/ ) {
      splice @file_array, ++$i, 0, 'a';
   }
   $i++;
}
untie @file_array;

 

[KevinADC]

KevinADC, I decided to test the code since there was some uncertainty.