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Re^4: how to use perl variable in system command to run on unix

by tousifp (Novice)
on Sep 03, 2013 at 17:28 UTC ( #1052151=note: print w/ replies, xml ) Need Help??


in reply to Re^3: how to use perl variable in system command to run on unix
in thread how to use perl variable in system command to run on unix

Thank you very much. But why $9 is escaped? Me new to perl !!!


Comment on Re^4: how to use perl variable in system command to run on unix
Re^5: how to use perl variable in system command to run on unix
by Laurent_R (Vicar) on Sep 03, 2013 at 17:53 UTC

    Because $9 is a variable in Perl, the ninth capture in a regular expression. Since you don't have a regex before, it is an undefined variable in your case, so il will be omitted altogether from your command line. If you escape the $ sign, you say that you want a $ sign, not a variable called $9. Then it is not interpolated and passed to awk correctly.

      Thanks buddy.

Re^5: how to use perl variable in system command to run on unix
by Arunbear (Parson) on Sep 04, 2013 at 09:50 UTC
    Because in this case you want a literal "$9", you don't want it to be expanded by Perl. An example that you can experiment with:
    % date Wed Sep 4 10:41:55 BST 2013 % date | awk '{ print $2 }' Sep % perl -de0 Loading DB routines from perl5db.pl version 1.32 Editor support available. Enter h or `h h' for help, or `man perldebug' for more help. main::(-e:1): 0 DB<1> $cmd = qq[date | awk '{ print $2 }'] DB<2> p $cmd date | awk '{ print }' DB<3> p qx/$cmd/ Wed Sep 4 10:47:41 BST 2013 DB<4> $cmd = qq[date | awk '{ print \$2 }'] DB<5> p $cmd date | awk '{ print $2 }' DB<6> p qx/$cmd/ Sep DB<7> q %
      Thanks. I got it. Will try your code later surely.

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