If you're typing

makeupscript.pl -c *.txt
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on your shell's command line, the shell will expand that to

makeupscript.pl -c foo.txt bar.txt baz.txt ...
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and pass on the expanded file names to the perl script. However, if you prevent expansion by saying

makeupscript.pl -c '*.txt'
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then your script will indeed find *.txt somewhere in @ARGS. To do the expansion yourself, check perldoc -f glob.