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# Write to text file:
open(my $fh, ">", $filename)
...
my $line = <$fh>;              # Reads a line.
chomp $line;                   # Removes eol chars (CR,LF)
close $fh;

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

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