Run sed command in perl script

Question

I am unable to invoke the sed command from the perl script as below:

#!/usr/bin/perl 
my $cmd = ('sed 's/...........//;s/............$//' a_file.txt >> a_newfile.txt');
  system($cmd);

Below is the error:

String found where operator expected at ./test.pl line 2, near "s/............$//' a_file.txt >> a_newfile.txt'"
syntax error at ./test.pl line 2, near "'sed 's/...........//"
syntax error at ./test.pl line 2, near "s/............$//' a_file.txt >> a_newfile.txt'"
Execution of ./test.pl aborted due to compilation errors.

I need to remove the <shortname>u********.com</shortname> in the file and save the output in a new file. Which commands do I need to run?

Answer 1

Ignoring for now the fact that perl can do better anything that sed can do, here to quote the shell command line to pass to system(), best would be to use the q{...} type of quotes:

my $cmd = q{sed 's/...........//;s/............$//' a_file.txt >> a_newfile.txt};

(assuming the ... part doesn't contain unbalanced {/}, if it does, you can use q@...@, q[...], q(...)...).

Because you do want a shell to interpret that command line (for the >> redirection), you want $cmd to be a scalar, not array (anyway arrays are named @cmd, not $cmd).

For perl to run the sed command by itself, that is without invoking a shell, you'd do:

my @cmd = ('sed', q{s/...........//;s/............$//}, 'a_file.txt');
system(@cmd);

But then, you'd need to do the stdout redirection in perl beforehand. Like:

open STDOUT, '>>', 'a_newfile.txt' or die "open: $!"

To do the whole thing in perl instead:

open my $in, '<', 'a_file.txt' || die "open a_file: $!";
open my $out, '>>', 'a_newfile.txt' || die "open a_newfile: $!";

while (<$in>) {
  s/...........//;s/............$//;
  print $out $_;
}
close $in;
close $out;