[SOLVED] writing substituted string into a file using PERL

rohitchauhan · 09-04-2013, 01:36 AM

Hi,
i am trying to replace a string in a file but i could not redirect the changed string in the file itself.

file location: /root/Desktop/resolv.conf
content:
search example.com
nameserver 8.8.8.8

required content:
search redhat.com
nameserver 8.8.8.8

Here is what i did:
program:

#!/usr/bin/perl

unless (open(INFILE, "resolv.conf")) {
die ("cannot open input file resolv.conf\n");
}
unless (open(OUTFILE, ">resolv.conf")) {
die ("cannot open output file resolv.conf\n");
}

$line=<INFILE>;
s/example/redhat/g;

while ($line ne "") {
print OUTFILE ($line);
$line = <INFILE>;
}

exit 0;

In my case both source and destination file is same. It is very simple using SED command i.e.:
sed -i 's/^ONBOOT=no/ONBOOT=yes/' /etc/sysconfig/network-scripts/ifcfg-eth0

The above command will make changes in the file itself.
I need same kind of thing in Perl.

one more thing, I need to do this in a script file not by using a one liner.

Any help is appriciated.

druuna · 09-04-2013, 03:04 AM

You cannot open a file for reading and writing at the same time.

One way to overcome this is to read the complete file into an array an go from there. Have a look at this:

Code:

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

my @array ;
my $line ;

# read fileinto array
open( INFILE, "<resolv.conf" )
  or die "Can't open resolv.conf : $!\n" ;
@array = <INFILE> ;
close( INFILE ) ;

# open file for writing and change content
open( INFILE, ">resolv.conf" )
  or die "Can't open resolv.conf : $!\n" ;
foreach $line ( @array ) {
  $line =~ s/example.com/redhat.com/g ;
  print INFILE "$line" ;
}
close( INFILE ) ;

exit 0 ;

rohitchauhan · 09-18-2013, 01:17 AM

Sorry for the delay, but I got it working now.
Here I am posting the new code for a different file. similar code should be working in same type of scenario.

Here is what I did to get it running:

$file="/root/Desktop/ifcfg-eth0-modified";
open (IN, $file) || die "vant open file: $!";

@lines=<IN>;
close IN;

open (OUT, ">", $file) || die "cant open file: $!";
foreach $line (@lines)
{
$line =~ s/^BOOTPROTO=none/BOOTPROTO=static/i;
$line =~ s/^ONBOOT=no/ONBOOT=yes/i;
$line =~ s/^UUID/#UUID/i;
$line =~ s/^HWADDR/#HWADDR/i;
$line =~ s/^IPADDR/#IPADDR/i;
$line =~ s/^NETMASK/#NETMASK/i;
$line =~ s/^GATEWAY/#GATEWAY/i;
$line =~ s/^DNS/#DNS/i;
print OUT "TYPE=Bridge";
}

open (OUT, ">>", $file) || die "cant open file: $!";
print OUT "TYPE=Bridge";

close OUT;

Thanks for your time and efforts.

rohitchauhan · 09-18-2013, 01:20 AM

The above code can be used to make changes i.e. string replacement in the source file and later adding a new line in the end of the same file.

I hope there is another better way of doing this...

though, marking it as solved now!

pan64 · 09-18-2013, 01:24 AM

what do you mean by better way? in such simple cases sed may be a better idea:
sed -i "s/^BOOTPROTO=none/BOOTPROTO=static/i;s/^ONBOOT=no/ONBOOT=yes/i; ... ' <filename with path>
will work, just you need to make a backup before any changes.