Unexpected Behavior - Variables and Regex

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

Good morning, fellow Monks. I am working on a script where I am seeing totally unexpected behavior. I am hoping one of you fine folks can get me back on the right path with this issue...

On my *nix server, I can run the following command to extract the first part of the hostname:

ABCXYZ123-0-0-1:/home/dir-> hostname | sed 's/-.*?//g'
ABCXYZ123
[download]

So I translated that into my Perl script. I am then running another command to create a couple of files, then checking the output of the command to ensure they were created with no issues. Well, my regex was failing (even though I know it was working properly) so I sucked out all the appropriate lines from my big script and put them into a test script (server names and some info changed to protect company data):

#!C:/Perl64/bin/perl.exe

use strict;
use warnings;
use Control::CLI;

my $cli;
my $output;
my $temp;
my $junk;

#my $host = "1.11.1.11";
my $host = "1.12.1.12";

$cli = new Control::CLI( Use    => 'SSH',
                         Timeout    => 180,
                       );

$cli->connect(  Host            => $host,
                Username        => 'user',
                Password        => 'pass',
             );

$output = $cli->cmd("clear");
$output = "";

my $hostname = $cli->cmd("hostname | sed \'s/-.*//g\'");
print "hostname: $hostname";

$junk = $cli->print("su -c \"/some/dir/path/here/command.py -o /dir\""
+);
$output = $cli->cmd("rootpwd");
print "\n$output\n";

#if ( $output =~ m/.*$hostname.ext.*/s && $output =~ m/.*name.ext.*/s 
+) {
if ( $output =~ m/$hostname/s ) {
    print "\t$hostname.ext and name.ext created successfully on server
+ in /spdata...\n";
} else {
    print "\tThere was a problem generating $hostname.ext and name.ext
+ on server in /spdata... Please investigate and start application aga
+in... Exiting program.\n";
    exit;
}

$cli->disconnect;
[download]

When I run this script stub, I get the following on my command prompt of my laptop:

C:\Users\ImJustAFriend\Documents\Perl\Test>CLIControlTest.pl
hostname: ABCXYZ123

Password:
Last login: Mon Jan 13 13:26:40 UTC 2014 from blah on ssh
/spdata/ABCXYZ123.ext is generated
/spdata/name.ext is generated

        There was a problem generating ABCXYZ123
.ext and name.ext on server in /spdata... Please investigate and start
+ application again... Exiting program.

C:\Users\ImJustAFriend\Documents\Perl\Test>
[download]

So I noticed the new line between "ABCXYZ123" and ".ext" in my output. Thinking this was the issue, I put in a "chomp($hostname);" line in my script, right after the "my $hostname=" line. When I ran it again, I got this output:

C:\Users\ImJustAFriend\Documents\Perl\Test>CLIControlTest.pl
hostname: ABCXYZ123

Password:
Last login: Mon Jan 13 13:26:40 UTC 2014 from blah on ssh
/spdata/ABCXYZ123.ext is generated
/spdata/name.ext is generated

.ext and name.ext on server in /spdata... Please investigate and start
+ application again... Exiting program.

C:\Users\ImJustAFriend\Documents\Perl\Test>
[download]

So putting the "chomp" in killed the whole beginning of my line. I have spent quite a few cycles on this, and still don't know what's going on. Can anyone provide some insight as to what the issue is here?

Thanks in advance!!

Comment on Unexpected Behavior - Variables and Regex Select or Download Code

Replies are listed 'Best First'.
Re: Unexpected Behavior - Variables and Regex by tobyink (Canon) on Jan 13, 2014 at 14:16 UTC
Firstly, make sure that you're not doing something like: `$foo = chomp($foo); # remove trailing line` [download] That doesn't work. `chomp` modifies `$foo` in place, and then returns a fairly useless value, so you don't want to then assign that to `$foo`. If that's not the case, then at a guess, `$hostname` might end in "\r\n" (a Windows-style line ending); perhaps because SSH knows you're connecting from a Windows host. In this case, `chomp` may be removing the "\n", but not the "\r". Outputting an "\r" results in the cursor returning to the start of the line; subsequent output will then overwrite your old output. Perhaps instead of `chomp($hostname)` try `$hostname =~ s(\s)()g` which will remove all whitespace from the host name. `use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name`	[reply] [d/l] [select]
Re: Unexpected Behavior - Variables and Regex by ImJustAFriend (Scribe) on Jan 13, 2014 at 14:26 UTC
OK, I did some googling for "Perl remove newline" and came across a technique that worked where chomp failed. Instead of "chomp($hostname)", I used this regex: `$hostname =~ s/\R//g;` [download] Now when I run my code, the regex match and the print output all works as expected. I hope this can help someone else in the future!! ImJustAFriend	[reply] [d/l]
Re^2: Unexpected Behavior - Variables and Regex by kcott (Archbishop) on Jan 13, 2014 at 14:49 UTC
Just some additional information: `\R` is described in perlrebackslash: Misc. It requires Perl 5.10.0. -- Ken	[reply] [d/l]