How do I escape a :: in s///?

xjlittle has asked for the wisdom of the Perl Monks concerning the following question:

Hello monks,

I have the following script where I want replace a line in my groups file with a new line containing new group members.
Here is my code:

#!/usr/bin/perl -w
use strict;

my $group = "sbo";
my $newstring = "sbo::18659:x0929,x1465,x1368,x5552;
my $backup = "/etc/group";
my $new = "/etc/group.tmp";

#back up group
`cp -f $backup $backup.4623`;

#fix group
open (GROUP, "<", $backup);
open (NEW, ">", $new);

while (<GROUP>){
        s/^$group/$newstring/;
        print NEW $_;
}
close GROUP;
close NEW;

print "\n";
print "\n";
system("cat $backup |grep $group");
#system("ls -lad $dirs");
print "\n";
system("hostname");
print "\n";
[download]

Here is the original string and the output data. As you can see the output substitutes the string but then adds the :: and everything after it again. I haven't been able to figure out how to escape the :: to make it quit doing this. Please shed some light.

_DATA_
diff /etc/group /etc/group.tmp
104c104
< sbo::18659:x0929,x1465
---
> sbo::18659:x0929,x1465,x1368,x5552::18659:x0929,v1x1465,x1368,x5552
bash-2.05#
[download]

Thanks!

Comment on How do I escape a :: in s///? Select or Download Code

Replies are listed 'Best First'.
Re: How do I escape a :: in s///? by ikegami (Patriarch) on Aug 14, 2009 at 16:10 UTC
You only asked it to replace "sbo", not the whole line. I think you want `s/^$group:.*/$newstring/;` [download] or the clearer `$_ = "$newstring\n" if /^$group:/;` [download] I added "`:`" to the regex pattern so that you don't accidentally replace the group "`sboadmin`" (for example).	[reply] [d/l] [select]
Re: How do I escape a :: in s///? by JavaFan (Canon) on Aug 14, 2009 at 16:10 UTC
As you can see the output substitutes the string but then adds the :: and everything after it again. No, it doesn't. You asked it to replace the `sbo` part, and only the `sbo` part, and that's what `s///` did. If you want to replace the entire string, do something like: `$_ = "$newstring\n" if /^$group/;` [download] instead.	[reply] [d/l] [select]
Re: How do I escape a :: in s///? by SuicideJunkie (Vicar) on Aug 14, 2009 at 16:11 UTC
That is what you told it to do... replace only the `$group` (if it occurs at the start of a line) with `$newstring`. Everything other than the "sbo" is left untouched. Escaping :: doesn't make sense, and it doesn't need to be. Did you want to replace the whole line? If so you can do that with an if, or grab `.*` on the match side of your substitution.	[reply] [d/l] [select]
Re: How do I escape a :: in s///? by perlkiller (Acolyte) on Aug 14, 2009 at 18:13 UTC
You are missing a double quote at the end of fifth line: my $newstring = "sbo::18659:x0929,x1465,x1368,x5552; should be `my $newstring = "sbo::18659:x0929,x1465,x1368,x5552";` [download]	[reply] [d/l]
Re: How do I escape a :: in s///? by perlkiller (Acolyte) on Aug 14, 2009 at 19:20 UTC
Actually you should use File::Tie module. It is a better module to use. Try to avoid running shell commands if you can. `#!/usr/bin/perl use warnings; use strict; use Tie::File; use File::Copy; use Sys::Hostname; my $host = hostname; my $group = 'sbo'; my $newstring = 'sbo::18659:x0929,x1465,x1368,x5552'; my $backup = "/tmp/groups"; copy ("$backup", "$backup.tmp") or die "can not copy $backup"; tie my @lines, 'Tie::File', "$backup" or die "can not open $backup $!" +; for (@lines) { if (/$group/) { $_ .= $newstring; last; } } untie @lines; print "\n $host \n";` [download]	[reply] [d/l]
Re^2: How do I escape a :: in s///? by ikegami (Patriarch) on Aug 14, 2009 at 19:56 UTC
I disagree. It's a huge waste of resources and it doesn't simplify anything. Compare `copy($groups_qfn, $backup_qfn) or die("Can't backup $groups_qfn\n"); tie(my @lines, 'Tie::File', $groups_qfn) or die("can not open $groups_qfn: $!\n"); for (@lines) { if (/^$group:/) { $_ = "$newstring\n"; last; } } untie @lines;` [download] with `copy($groups_qfn, $backup_qfn) or die("Can't backup $groups_qfn\n"); open(my $in_fh, '<', $backup_qfn) or die("Can't open $backup_qfn: $!\n"); open(my $out_fh, '>', $groups_qfn) or die("Can't open $groups_qfn: $!\n"); while (<$in_fh>) { if (/^$group:/) { $_ = "$newstring\n"; } print $out_fh $_ }` [download]	[reply] [d/l] [select]