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Re: Linux file handle not working

by shmem (Chancellor)
on Jan 16, 2020 at 01:36 UTC ( #11111468=note: print w/replies, xml ) Need Help??

in reply to Linux file handle not working

The shell quoting rules are different between Windows and Linux/UNIX. Within double quotes (") the $ sign is significant to the Linux/UNIX shell. Try:

>perl -Mntheory=:all -nE 'chomp; say is_prime($_);' input.txt

The argument for the -e flag is surrounded with " on Windows, but with ' on Linux/UNIX. Quoting rules therefore are different in the body of the script provided via -e, which led iirc to the q() family of operators (see perlop)

update: the _ identifier is set in the shell to the last argument of the previous command, so $_ is set to input.txt which is interpolated into the program string passed to perl via -e as the expression of concatenation of two barewords:

qwurx [shmem] ~> perl -E "say '$_'" qwurx [shmem] ~> perl -E "say '$_'" qwurx [shmem] ~> perl -E "say $_" foobar

This is a dangerous thing, if the last argument of the previous line happens to contain metacharacters, e.g.

qwurx [shmem] ~> echo '`ls -l /dev/null`' `ls -l /dev/null` qwurx [shmem] ~> perl -E "say $_" crw-rw-rw- 1 root root 1, 3 Nov 27 11:02 /dev/null qwurx [shmem] ~> perl -MO=Deparse -E "say $_" use feature 'current_sub', 'evalbytes', 'fc', 'say', 'state', 'switch' +, 'unicode_strings', 'unicode_eval'; say say(say(`ls -l /dev/null`)); -e syntax OK

so don't do that.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

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