You should always post the exact error message you are getting. Use "code" tags.

Your use strict; statement is embedded in a comment line, and is therefore not in effect. Put it on its own line, and you will get compile errors regarding OUT and $OUT.

Using the following:

• use strict and warnings
• open
• perlcritic

I'd re-write the code as (UNTESTED):

use strict;
use warnings;

my $fin  = "SELECTDAT2";
my $fout = "myfile";
open my $ih, '<',  $fin  or die "cannot open $fin for reading, $! ";
open my $oh, '>',  $fout or die "cannot open $fout for writing, $! ";
while (<$ih>) {
    print $oh "NO", "\n", " 'SOURCE' ", "SEC", "Q", "SEC", "\n", "LONG
+", "LAT", "DEPTH", "GAP";
}
close $oh;
close $ih;
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