how should I use system command in perl - perl

Question

I want to replace a line with the $var.
runnew has
input= input/old/should/change;
replace= input/old/replace;
other = input/old/other;
replace_other= input/old/replace_other;
My output file should look like,
input= input/old/should/New;
replace= input/old/New_replace;
other = input/old/New_other;
replace_other= input/old/New_replace_other;
I want to replace "input =" by input = input/old/should/New;
I have used like,
if ($#ARGV != 0) {
die "\n********USAGE <cellname> <tech>********\n";
}
$newinput=$ARGV[0];
open(my $fh, "$runnew") or die "Could not open rerun.txt: $!";
while (<$fh>) {
system ( sed -i "/input=.*/c\input= $newinput" $runnew );
}
But there is error popping up "Scalar found where operator expected at run.pl" and its displaying sed line and asking " (Missing operator before $runnew?)."
When I used same sed on terminal its replacing the line .
Please can anyone point out where the error is ?
Yes Using Sed is simple but I have file with different lines and each line should be replaced .
Please let me knoe if you have better idea than this.
Thanks in advance.

Answer 1

system() takes a list of strings as its argument. You you need to put quotes around the command you pass it.
system ( "sed -i '/input=.*/c\input= $newinput' $runnew" );
But your code still looks very strange. You're running exactly the same sed command for every line in the input file. Is that what you meant to do?
It's not really clear what you're trying to do here. But I'm confident that the best approach would involve not using sed and using Perl to make your transformations.

Answer 2

Why do you want to call sed at all? Your requirement can be much easier handled in Perl directly:
add -i.bak to enable in-place replacement mode
use the first command line parameter as replacement string
remove it from the #ARGV array so it will not be interpreted as file
loop over all files on the command line
read line by line
apply substitution
print result
Perl automatically takes care of opening the files, writing to the correct file and renaming old files to .bak.
#!/usr/bin/perl -i.bak
use warnings;
use strict;
my($replacement) = shift(#ARGV);
while (<>) {
s/input=.*/input= $replacement/;
print;
}
exit 0;
Test run (taking an educated guess on your input data):
$ cat dummy1.txt.bak
input= test1
input= test2
$ cat dummy2.txt.bak
input= test3
input= test4
$ perl dummy.pl REPLACEMENT dummy1.txt dummy2.txt
$ cat dummy1.txt
input= REPLACEMENT
input= REPLACEMENT
$ cat dummy2.txt
input= REPLACEMENT
input= REPLACEMENT
or to use the contents of the file "rerun.txt":
$ perl dummy.pl REPLACEMENT $(cat rerun.txt)