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Re: Having to manually escape quote character in args to "system"?

by Anonymous Monk
on Sep 12, 2017 at 14:35 UTC ( #1199202=note: print w/replies, xml ) Need Help??

in reply to Having to manually escape quote character in args to "system"?

Always search CPAN first, to find good things like ShellQuote::Any::Tiny.
  • Comment on Re: Having to manually escape quote character in args to "system"?

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Re^2: Having to manually escape quote character in args to "system"?
by vr (Friar) on Sep 13, 2017 at 11:26 UTC

    Thank you, everyone, for very enlightening answers, I've learned quite a few things from them.

    Unfortunately, ShellQuote::Any::Tiny doesn't do it right:

    >perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say f +or @ARGV; <STDIN>', 1, shell_quote(qq(\x5c \x5c)), 2" 1 \\ \ 2

    because it escapes every backslash. But only terminating one, which precedes the closing double-quote (if any), should be escaped -- as follows from "Everyone quotes command line arguments the wrong way".

    Win32::ShellQuote appears to handle everything correctly.

    Actually, I lived happily before this, relying only on Perl's built-in ability to double-quote arguments, which contain spaces. Until someone, in her wisdom, decided that a double-quote in the middle of template name, to be passed as argument to another script, is a good idea.

      > Unfortunately, ShellQuote::Any::Tiny doesn't do it right:

      Bug reported.

      ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
      The bug has been fixed (see my other comment for the link). Can you check?

      ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

        Thank you for reporting a bug for me, in the first place. No, fix is not good (I notified the author). Similar test fails:

        >perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say f +or @ARGV', 1, shell_quote(qq(\x5c\x5c \x5c)), 2" 1 \\\ \ 2

        According to comment in source, [we now] "escape backslash that is followed by a backslash, or the last backslash". That's not what rules 4-7 in MS guidelines say, if we 'reverse' them. 'Reverse', because they say how to parse a command line, and, of course, Perl does it OK for all test cases provided on that page:

        perl -E "system $^X, '-E', 'say for @ARGV', qq(\x22abc\x22 d e)" perl -E "system $^X, '-E', 'say for @ARGV', qq(a\x5c\x5c\x5cb d\x22e f +\x22g h)" perl -E "system $^X, '-E', 'say for @ARGV', qq(a\x5c\x5c\x5c\x22b c d) +" perl -E "system $^X, '-E', 'say for @ARGV', qq(a\x5c\x5c\x5c\x5c\x22b +c\x22 d e)"

        While we need the opposite: to escape arguments, so that when Perl #1 simply glues them together, another program (e.g. Perl #2) breaks the CL to the same arguments. Line 24

        $arg =~ s/(\\(?!.*\\)|\\(?=\\)|")/\\$1/g;

        could be replaced with

        $arg =~ s/\\(?=\\*(?:"|$))/\\\\/g; $arg =~ s/"/\\"/g;

        Then round-trip tests pass OK (though they are trivial, of course):

        perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say fo +r @ARGV', map {shell_quote $_} qw(abc d e)" perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say fo +r @ARGV', map {shell_quote $_} qq(a\x5c\x5c\x5cb), 'de fg', 'h'" perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say fo +r @ARGV', map {shell_quote $_} qq(a\x5c\x22b), 'c', 'd'" perl -MShellQuote::Any::Tiny=shell_quote -E "system $^X, '-E', 'say fo +r @ARGV', map {shell_quote $_} qq(a\x5c\x5cb c), 'd', 'e'"

        Edit. P.S. Issue fixed (on the same day) in 0.007 version. I'm out of issues.


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