Robin Smidsrød

I was filtering some output in the shell today, and I reached for my trusty awk '{ print $1 }' to get the first part of a line separated by whitespace.

Then I started to think; why am I using awk for this when I know so much perl, and perl is supposed to be so good at text parsing?

I asked the question on #perl-help on irc.perl.org. A friendly user, daxim, started helping me out and quickly re-educated me on the -l, -a and -F parameters to perl:

$ perl --help
  -F/pattern/       split() pattern for -a switch (//'s are optional)
  -l[octal]         enable line ending processing, specifies line terminator
  -a                autosplit mode with -n or -p (splits $_ into @F)

  -n                assume "while (<>) { ... }" loop around program
  -p                assume loop like -n but print line also, like sed
  -e program        one line of program (several -e's allowed, omit programfile)

As the default for -F is \s+, we can skip it when we're splitting on whitespace. And adding -l enables automatic "\n" on that print statement. That makes the perl equivalent quite similar to the awk method (and easier to memorize):

$ ls -l | perl -lane 'print $F[0]' # gives you the file modes only from ls

A nice side-effect of this is that perl has a very compact array slice syntax, so if you want to fetch multiple values, you can do something like this:

$ ls -l | perl -lane 'print @F[0,2..3] # file modes and owner/group information

Just remember that perl method (@F) starts counting at 0, while the awk method starts counting at 1.