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Linux file handle not working

by pvfki (Novice)
on Jan 16, 2020 at 00:46 UTC ( #11111465=perlquestion: print w/replies, xml ) Need Help??

pvfki has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am trying to run a perl command through linux console using filehandle ($_ sign) in order to indicate a file to use when running the command. The commands from the code snippet below are from https://metacpan.org/pod/ntheory

For example, I have the following number in input.txt: 147416345806550029415781910597841
Running with Windows:
>perl -Mntheory=:all -nE "chomp; say is_prime($_);" input.txt 1 >perl -Mntheory=:all -nE "chomp; say length($_);" input.txt 33
Running on Linux however I get:
>perl -Mntheory=:all -nE "chomp; say is_prime($_);" input.txt Parameter 'inputtxt' must be a positive integer at -e line 1, <> line +1. >perl -Mntheory=:all -nE "chomp; say length($_);" input.txt Parameter 'inputtxt' must be a positive integer at -e line 1, <> line +1.
Does anyone know how to fix this? I'm not sure how perl (shell) via Linux works? How do I get the same output as Windows? Thanks for help!

Replies are listed 'Best First'.
Re: Linux file handle not working
by shmem (Chancellor) on Jan 16, 2020 at 01:36 UTC

    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 '$_'" foo.bar qwurx [shmem] ~> perl -E "say '$_'" foo.bar foo.bar qwurx [shmem] ~> perl -E "say $_" foo.bar 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'
Re: Linux file handle not working
by 1nickt (Abbot) on Jan 16, 2020 at 01:33 UTC

    Hi,

    Works for me with Math::Prime::Util v.073 on MacOS with Perl 5.30.1 and on Ubuntu with Perl 5.28.1 :

    $ echo 147416345806550029415781910597841 > input.txt
    $ perl -Mstrict -Mntheory=:all -wnE 'chomp; say is_prime($_);' input.t +xt 1
    $ perl -Mstrict -Mntheory=:all -wnE 'chomp; say length($_);' input.txt 33

    Hope this helps!


    The way forward always starts with a minimal test.

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