Again, escape of '$' is necessary for bash shell which used at unix-like system 
perl -e "$_='qwerty'; s/r/print pos(). \"\n\";/e; print $_;"
syntax error at -e line 2, near "="
Execution of -e aborted due to compilation errors.

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but then $ is escaped 
perl -e "\$_='qwerty'; s/r/print pos(). \"\n\";/e; print \$_;"
3
qwe1ty

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It seems you try your example under windows, and it is work fine there, but i'm macos user. 1(one) is returned by print function and s/// insert it because it is last return at executed section, this is clear, but it can be easily fix 
perl -e "\$_='qwerty'; s/r/print pos(). \"\n\";\$&/e; print \$_;"
3
qwerty

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In reply to Re^10: Using pos() inside regexp (no /e) by braveghost
in thread Using pos() inside regexp by braveghost

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