How can I check that Perl isn't setting any environment variables?

AFAIK, it doesn't. If you don't, that is. OTOH under *NIX it is possible to detect whether a file descriptor is connected to a tty or not, which is often used to "understand" whether a program's STDOUT is being piped or redirected to a file or not. (This is what e.g. ls(1) does under recent releases of Linux, at least: it acts like ls -1 if you pipe it to something else, and similarly if you set --color=auto it will print coloured output on the terminal, but will disable it when piping or redirecting to a file - in fact the switch is set by default in many distros.) Maybe under windows it's the same. Let me see: 

C:\temp>perl -le "open F, '>F'; print -t *F; print -t *STDOUT"

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In reply to Re^3: Perl ignores lines with bold characters from a pipe on Windows (source not dest) by blazar
in thread Perl ignores lines with bold characters from a pipe on Windows by kingkongrevenge

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