# Write to text file:
open(my $fh, ">", $filename)
    or die "Failed open for write! $!";
print $fh "Foo\n";             # Prints to file
close $fh;                     # Close file

# Read from text file:
open($fh, "<", $file_to_read) or die "Couldn't open! $!";
my $line = <$fh>;              # Reads a line.
chomp $line;                   # Removes eol chars (CR,LF)
close $fh;

##</code><code>##

perl -e 'open($fh, ">", "tst") or die "$!"; print $fh "XX\n"; close $fh;'

##</code><code>##

perldoc -f open
perldoc perldoc
perldoc perlrun
perldoc Tk      # (Added as Edit.)