$ cat pm_year_make_model_file_models.master
Sorento
Cavalier
Expedition

##</code><code>##

$ cat >> pm_year_make_model_file_models.master
Expedition XLT

##</code><code>##

$ rm pm_year_make_model_temp_file

##</code><code>##

$ 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

##</code><code>##

$ cat pm_year_make_model_file_models.used
Sorento
Cavalier
#Expedition
Expedition XLT

##</code><code>##

$ 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

##</code><code>##

$ cat pm_year_make_model_file_models.used
Sorento
Cavalier
#Expedition
#Expedition XLT