Question

Say I have a data file that I want to process; I want to take the maximum value of each of the column and append it to the end of each line.

INPUT:

T1 T2 T3
35.82 34.67 31.68
32.20 34.52 33.59
37.41 38.64 37.56

OUTPUT:

T1 T2 T3
35.82 34.67 31.68 35.82
32.20 34.52 33.59 34.52
37.41 38.64 37.56 38.64

I’m trying to implement this as a one-liner. So far, this is what I’ve come up with, although it complains that &main::max is undefined:

perl -MList::Util -ani.bak -e "print qq(@F).q( ).max(@F).qq(\n)" file1.txt

It seems that I haven’t loaded the List::Util module. What’s wrong? And is the header column an issue?

perlrun doesn’t have a decent example on how to do this (actually it does, my documentation was a little hard to read).

Answer 1

You loaded List::Util, but the module doesn’t export symbols by default. Skip the header line by checking whether $. is 1.

$ perl -MList::Util=max -ape 's/$/" " . max(@F)/e unless $.==1' input 
T1 T2 T3
35.82 34.67 31.68 35.82
32.20 34.52 33.59 34.52
37.41 38.64 37.56 38.64

The perlrun documentation explains:

A little builtin syntactic sugar means you can also say -mmodule=foo,bar or -Mmodule=foo,bar as a shortcut for -Mmodule qw(foo bar). This avoids the need to use quotes when importing symbols. The actual code generated by -Mmodule=foo,bar is use module split(/,/,q{foo,bar}). Note that the = form removes the distinction between -m and -M.