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.

In reply to Re^5: how to use perl variable in system command to run on unix by Laurent_R
in thread how to use perl variable in system command to run on unix by tousifp

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