without commenting on the sanity of this approach in general (ie, obligatory mention of IO::Prompt), here are some comments about this particular code:

1. always use strict;
2 (related). declare your variables in the appropriate scope
3. your code always prints "Invalid input" even when it is valid -- you want to print that only if they have typed something already.
4. you 'redo FILENAME' without resetting $save, so your while ($save !~ ...) fails the second time through
5. your open/print/close is within the if (-e $save) block, so it never happens if the file does not already exist
6. the {1} in your regular-expressions is useless, since 1 is the default.
7. you could use m/^[SF]$/i to match case-insensitively (/i means ignore-case), but i won't bother with that in the code below..

here is a revised version. i have tried to change as little as possible to make it work, so you can learn from your mistakes rather than be confronted with entirely new/unfamiliar code. 

use strict;
my $output = "here is some output\n";  # for testing.. your output can
+ come from whereever

my $out;
while ( $out !~ m/^[sSfF]$/ ) {
    print("\nInvalid input.\n Please type either S or F.\n")
        if $out;
    print("Do you want to output to (S)creen or to (F)ile?\n");
    chomp( $out = <STDIN> );
}

if ( $out =~ m/^[sS]$/ ) {
    print $output;

} elsif ( $out =~ m/^[fF]$/ ) {

    my $save;   # this is outside the FILENAME:{} block because it is 
+needed at the end
    FILENAME: {
        while ( $save !~ (m/^[a-zA-Z][a-zA-Z_0-9]*$/) ) {
            print("\nInvalid input.\n Please begin with a letter and d
+o not add extension, it will be added automatically.\n")
                if $save;
            print("Please enter filename:\n");
            chomp( $save = <STDIN> );
        }

        if ( -e $save ) {
            my $overwrite;
            while ( $overwrite !~ (m/^[nNyY]$/) ) {
                print("\nInvalid input.\n Please type either Y or N.\n
+")
                    if $overwrite;
                print("\nFilename exists. Overwrite? (Y) or (N)\n");
                chomp( $overwrite = <STDIN> );
            }
            if ( $overwrite =~ (m/^[nN]$/) ) {
                undef $save;    # reset $save to trigger new prompt!
                redo FILENAME;
            }
        }
    }

    open( DATA, ">$save" ) || die "Couldn't open $save for writing: $!
+\n";
    print DATA $output;
    close(DATA);

}

[download]

In reply to Re^3: returning to a loop later on by mreece
in thread returning to a loop later on by Yoda_Oz

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