Programmatically read from STDIN or input file in Perl

Question

What is the slickest way to programatically read from stdin or an input file (if provided) in Perl?

Answer 1

The "slickest" way in certain situations is to take advantage of the -n switch. It implicitly wraps your code with a while(<>) loop and handles the input flexibly.

In slickestWay.pl:

#!/usr/bin/perl -n

BEGIN: {
  # do something once here
}

# implement logic for a single line of input
print $result;

At the command line:

chmod +x slickestWay.pl

Now, depending on your input do one of the following:

1. Wait for user input

   ./slickestWay.pl
   

2. Read from file(s) named in arguments (no redirection required)

   ./slickestWay.pl input.txt
   ./slickestWay.pl input.txt moreInput.txt
   

3. Use a pipe

   someOtherScript | ./slickestWay.pl 
   

The BEGIN block is necessary if you need to initialize some kind of object-oriented interface, such as Text::CSV or some such, which you can add to the shebang with -M.

-l and -p are also your friends.