sed "unterminated `s'command`" error when running from a script

Question

I have a temp file with contents:

a 
b
c
d
e

When I run sed 's#b#batman\nRobin#' temp from command line, I get:

a
batman
Robin
c
d
e

However, when I run the command from a Perl scriptL

#!/usr/bin/perl

use strict;
use warnings;

`sed 's#b#batman\nRobin#' temp`

It produces error:

sed: -e expression #1, char 10: unterminated `s' command

What am I doing wrong?

Answer 1

Why run another tool like sed once you are inside a Perl program? If anything, now you have far more tools and power so just do it with Perl.

One simple way to do your sed thing

use warnings;
use strict;

die "Usage: $0 file(s)\n" if not @ARGV;

while (<>) { 
    s/b/batman\nRobin/;
    print;
}

Run this program by supplying the file (temp) to it on the command line. The die line is there merely to support/enforce such usage; it is inessential for script's operation.

This program then is a simple filter

• <> operator reads line by line all files submitted on the command line

• A line is assigned by it to $_ variable, a default for many things in Perl

• The s/// operator by default binds to $_, which gets changed (if pattern matches)

• print by default prints the $_ variable

• Use nearly anything you want for delimiters in regex, see m// and s/// operators

This can also be done as

while (<>) {
    print s/b/batman\nRobin/r
}

With /r modifier s/// returns the changed string (or the original if pattern didn't match)

Finally that's also just

print s/b/batman\nRobin/r while <>;

but I'd expect that with a script you really want to do more and then this probablyisn't it.

On the other side of things you could write it more properly

use warnings;
use strict;
use feature qw(say);

die "Usage: $0 file(s)\n" if not @ARGV;

while (my $line = <>) { 
    chomp $line;

    $line =~ s/b/batman\nRobin/;

    say $line;
}

With a line in a lexical variable nicely chomp-ed this is ready for more work.