$ echo -e "123\n456\n789" > foo.txt
$ hexdump -C foo.txt
00000000  31 32 33 0a 34 35 36 0a  37 38 39 0a              |123.456.789.|
0000000c
$ cat foo.txt | perl -wle 'use strict; while(my $line = <>) { chomp $line; ($line =~ m/^\d+$/) ? print qq{number ok:"$line"} : print qq{number error:"$line"} }'
number ok:"123"
number ok:"456"
number ok:"789"
$ unix2dos foo.txt
unix2dos: converting file foo.txt to DOS format ...
$ hexdump -C foo.txt
00000000  31 32 33 0d 0a 34 35 36  0d 0a 37 38 39 0d 0a     |123..456..789..|
0000000f
$ cat foo.txt | perl -wle 'use strict; while(my $line = <>) { chomp $line; ($line =~ m/^\d+$/) ? print qq{number ok:"$line"} : print qq{number error:"$line"} }'
"umber error:"123
"umber error:"456
"umber error:"789
$