Two problems.

• You never put anything in $var, so unless you pass the empty string as an argument, it will never match.

• \u$1 is not valid Perl code. \u is for use in string literals. So drop the "e" modifier.

• By the way, the "g" modifier makes no sense either. How can ^ match more than once?

I think you meant

perl -le'($var = shift) =~ s/(.*)/\u$1/s; print $var' hi
[download]

But why the crazyness?

perl -le'print uc(shift)'
[download]

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