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

[Arunbear]

q does not expand variables, for that you need qq e.g.

% perl -E '$x = "hello"; say q($x)'
$x
% perl -E '$x = "hello"; say qq($x)'
hello

[tousifp]

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

[Laurent_R]

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.

[tousifp]

Thanks buddy.

[Arunbear]

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
%

[tousifp]

Thanks. I got it. Will try your code later surely.