Use of uninitialized value $ARGV[1] in substitution iterator

Question

I am trying to run this program that I wrote and I keep getting an error message that states the following

Use of uninitialized value $ARGV[1] in substitu

Answer 1

Don't forget that arrays are indexed from 0 in Perl, and the elements of @ARGV do not include the program name. You should probably be using $ARGV[0] and $ARGV[1]. You can check this by printing out the values of the array — index and value at the index.

See perldoc perlvar:

The array @ARGV contains the command-line arguments intended for the script. $#ARGV is generally the number of arguments minus one, because $ARGV[0] is the first argument, not the program's command name itself. See $0 for the command name.

Note that this means that if you run:

perl script.pl something or-another

the @ARGV array has two entries: something and or-another in elements 0 and 1 respectively. Similarly if the script is executable:

script.pl something or-another

If you check $ARGV[2], you will be using the default file name with either of the invocations shown — change the 2 to a 1. Also, you should be able to move the test and assignment to $outfile outside the loop, and only open that file just once. At the moment, you zap it for each new file, so effectively you only process the last file.