open a file and replace a word using perl - perl

Question

I want to open a file and replace a word from a file.
My code is attached here.
open(my $fh, "<", "pcie_7x_v1_7.v") or die "cannot open <pcie_7x_v1_7.v:$!";
while (my $line = <$fh>) {
if ($line =~ timescale 1 ns) {
print $line $msg = "pattern found \n ";
print "$msg";
$line =~ s/`timescale 1ns/`timescale 1ps/;
}
else {
$msg = "pattern not found \n ";
print "$msg";
}
}
File contains pattern timescale 1ns/1ps.
My requirement is to replace timescale 1ns/1ps to be replaced with timescale 1ps/1ps.
At present else condition occurs always.
Update code after receiving comment:
Hi,
Thanks for the quick solution.
I changed the code accordingly, but the result was not successful.
I have attached the updated code here.
Please suggest me if I missed anything here.
use strict;
use warnings;
open(my $fh, "<", "pcie_7x_v1_7.v" )
or die "cannot open <pcie_7x_v1_7.v:$!" ;
open( my $fh2, ">", "cie_7x_v1_7.v2")
or die "cannot open <pcie_7x_v1_7.v2:$!" ;
while(my $line = <$fh> )
{
print $line ;
if ($_ =~ /timescale\s1ns/ )
{
$msg = "pattern found \n " ;
print "$msg" ;
$_ =~ s/`timescale 1ns/`timescale 1ps/g ;
}
else
{
$msg = "pattern not found \n " ;
print "$msg" ;
}
print $fh2 $line ;
}
close($fh) ;
close($fh2) ;
Result:
pattern not found
pattern not found
pattern not found
pattern not found
Regards,
Binu
3rd update:
// File : pcie_7x_v1_7.v
// Version : 1.7
//
// Description: 7-series solution wrapper : Endpoint for PCI Express
//
//--------------------------------------------------------------------------------
//`timescale 1ps/1ps
`timescale 1ns/1ps
(* CORE_GENERATION_INFO = "pcie_7x_v1_7,pcie_7x_v1_7,

Answer 1

You can use a perl oneliner from a command line. No need to write a script.
perl -p -i -e "s/`timescale\s1ns/`timescale 1ps/g" pcie_7x_v1_7.v
-
However,
If you still want to use the script, you are almost there. You just need to fix a couple errors
print $line; #missing
if ($line =~ /timescale\s1ns/) #made it a real regex, this should match now
$line =~ s/`timescale 1ns/`timescale 1ps/g ; #added g to match all occurences in line
after the if-else you must print the line to a file again
for example, open a new file for writing (let's call it 'pcie_7x_v1_7.v.2') at the beginning of your script
open(my $fh2, ">", "pcie_7x_v1_7.v.2" ) or die "cannot open <pcie_7x_v1_7.v.2:$!" ;
then , after the else block just print the line (whether it's changed or not) to the file
print $fh2 $line;
Don't forget to close the filehandles when you're done
close($fh);
close($fh2);
EDIT:
Your main problem was that you used $_ for the check, while you had assigned the line to $line. So you did print $line, but then if ($_ =~ /timescale/. That would never work.
I'm copy pasting your script and made a couple corrections and formatted it a little more dense to better fit in the website. I also removed the if match check as suggested by TLP and directly did the substitution in the if. It has exactly the same result. This works:
use strict;
use warnings;
open(my $fh, "<", "pcie_7x_v1_7.v" )
or die "cannot open <pcie_7x_v1_7.v:$!" ;
open( my $fh2, ">", "pcie_7x_v1_7.v2")
or die "cannot open >pcie_7x_v1_7.v2:$!" ;
while(my $line = <$fh> ) {
print $line;
if ($line =~ s|`timescale 1ns/1ps|`timescale 1ps/1ns|g) {
print "pattern found and replaced\n ";
}
else {
print "pattern not found \n ";
}
print $fh2 $line ;
}
close($fh);
close($fh2);
#now it's finished, just overwrite the old file with the new file
rename "pcie_7x_v1_7.v2", "pcie_7x_v1_7.v";