Your original command line was 
cat some_file_holding3numbers.txt |  avg_routines.pl (+some way of spe
+cifying avg3())> avg.txt

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The more usual way of forming that is 
perl -w avg_routines.pl (+some way of specifying avg3()) <some_file_ho
+lding3numbers.txt >avg.txt

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That aside, if the routine you wanted to use was inside the existing script, you could name the routine on the command line then use 
  my $Routine = shift;  #  Get routine name from cmd line
  &{ $Routine };        #  Call named routine

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to actually run it (I haven't tried this code -- this is just something to get you pointed in the right direction). This routine would then read input from the command line via the diamond operator while (<>), average the three numbers and output the average using print.

If the code's in another module, you'll have to include the module name with the routine name, and either use it within your script or bring it in using the -M command line argument for Perl.

This sounds like an awfully complicated way to do something fairly simple. What problem are you really trying to solve?

--t. alex

"Of course, you realize that this means war." -- Bugs Bunny.

In reply to Re: routine as subroutine and on command line by talexb
in thread routine as subroutine and on command line by wah

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