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Slurp in Perl

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We all know, in Perl v5.36, a new command line flag -g was introduced. For more information you can checkout PPC-0011.

The new flag sets $/ (input record separator) to undef and therefore enables slurp mode.

It’s simply an alias for -0777.

Those who are old enough, might remember this -0777 magical number.

So what is -0777?

As per the official documentation:

-0[octal/hexadecimal] specify record separator (\0, if no argument)

0777 corresponds to the decimal value 511. In ASCII/Unicode, there is no character with the value 511.

It ensures that the input record separator ($/) will never match anything in the input data.

Is that the only magical number that can be used?

The short answer is No.

There are couple more that I remember for now: 0400 and 01000.

So technically, we can use any of these to enable slurp mode: -0777, -0400 or -01000.

Let’s see some action now.

For this, I would create a simple text file example.txt having just 3 lines to play with it.

  $ echo -e "Line 1\nLine 2\nLine 3" > example.txt

Let’s show the modern slurp mode.

  $ perl -gne 'print' example.txt
  Line 1
  Line 2
  Line 3
  $

How about if we do without -g?

  $ perl -ne 'print' example.txt
  Line 1
  Line 2
  Line 3
  $

So how do I know if slurp is actually happening at all?

This is easy to demonstrate.

  $ perl -gne 'print; $i++; END { print "Loop executed $i times\n" }' example.txt
  Line 1
  Line 2
  Line 3
  Loop executed 1 times
  $

How about without -g then?

  $ perl -ne 'print; $i++; END { print "Loop executed $i times\n" }' example.txt
  Line 1
  Line 2
  Line 3
  Loop executed 3 times
  $

Isn’t it magical?

Let’s go back to the magical numbers: -0777, -0400 and -01000.

We will use the magical numbers this time:

  $ perl -0777 -ne 'print; $i++; END { print "Loop executed $i times\n" }' example.txt
  Line 1
  Line 2
  Line 3
  Loop executed 1 times
  $

  $ perl -0400 -ne 'print; $i++; END { print "Loop executed $i times\n" }' example.txt
  Line 1
  Line 2
  Line 3
  Loop executed 1 times
  $

  $ perl -01000 -ne 'print; $i++; END { print "Loop executed $i times\n" }' example.txt
  Line 1
  Line 2
  Line 3
  Loop executed 1 times
  $

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CONCLUSION: If you are using Perl v5.36 or above then you don’t need to remember these magical numbers, instead just use -g. Happy hacking !!!