I can't reproduce the problem with the code I posted. You haven't shown what code you're using: see "How do I post a question effectively?" for guidelines on what to post such that we can help you.

Here's my test:

$ cat pm_year_make_model_file_models.master
Sorento
Cavalier
Expedition
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$ cat >> pm_year_make_model_file_models.master
Expedition XLT
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$ rm pm_year_make_model_temp_file
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$ pm_year_make_model.pl
Available years:
1999
2000
2001
Select year: 1999
Available makes:
Chevrolet
Ford
KIA
Select make: Ford
Available models:
Cavalier
Expedition
Expedition XLT
Sorento
Select model: Expedition
Temp file contents:
1999 Ford Expedition
[download]

$ cat pm_year_make_model_file_models.used
Sorento
Cavalier
#Expedition
Expedition XLT
[download]

$ pm_year_make_model.pl
Available years:
2000
2001
Select year: 2000
Available makes:
Chevrolet
KIA
Select make: KIA
Available models:
Cavalier
Expedition XLT
Sorento
Select model: Expedition XLT
Temp file contents:
1999 Ford Expedition
2000 KIA Expedition XLT
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$ cat pm_year_make_model_file_models.used
Sorento
Cavalier
#Expedition
#Expedition XLT
[download]

The added code is below. Since the program is actually sharing the master files which look like this:

Expedition:XLT:Power Locks:Power Doors

The code added strips the ":" and then joins only the two fields needed for my side of the program. I am not originating the files another program is doing that.

for (@models) {
my @mfields   = split /:/;
$_ = join ' ' => $mfields[0], $mfields[1];
}
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When selected the program only recognizes the first field not the second when joined together creating the following output:

##Expedition
Expedition XLT



Thus not commenting out each Expedition

FIXED!! Using the below code I have no issues splitting the fields and rejoining the fields using split and splice together. Thanks for the suggestions they have been most helpful.

for (@models) {
my @mfields   = split /:/, $_;
$_ = join ( ' ',splice( @mfields, 0, 2));
}
[download]