My guess is something in your call is doing some escape code interpretation which translates \t to tab.

Which is weird for Windows. ..

One workaround is to replace every \\ with ${bs} in your Perl code and to initialize it with $bs= chr (92), like this a literal backslash wouldn't show up.

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Update: or something is collapsing \\t to \t such that Perl sees a tab.

Anyway the problem is not in Perl but the surrounding shell .