Raku Books / Raku One-Liners / Command-Line Options

Using command-line options

Let us talk about the command-line options that the Rakudo1 compiler offers to us.

-e

The first option to know when working with Raku is -e. It takes a string with your Perl 6 one-liner and executes it immediately.

For example, print the name of the current user:

$ perl6 -e'$*USER'

ash

-n

This option repeats the code for each line of input data. This is quite handy when you want to process a file. For example, here’s a one-liner that adds up the values in a row and prints the sum:

$ raku -ne'say [+] .split(" ")' data.txt

If the data.txt file contains the following:

10 20 30 40
1 2 3 4
5 6 7 8

1 Rakudo (rakudo.org) is an implementation of Raku. The rest of the book assumes you are using the Rakudo compiler and run it as raku from command line. If you have an older version, which has the perl6 executable, make an alias in your .pro-

file: alias raku=perl6.

then the result of the one-liner is:

There’s no difference whether you use shell’s input redirection or not; the following line also works:

$ raku -ne'say [+] .split(" ")' < data.txt

Make sure you place the e option the last in the list (so, not raku -en'...') or split the options: raku -n -e'...'.

-p

This option is similar to -n but prints the topic variable after each iteration.

The following one-liner reverses the lines in the file and prints them to the console:

$ raku -npe'.=flip' data.txt

For the same input file, the result will look like this:

04 03 02 01
4 3 2 1
8 7 6 5

Notice that you have to update the $_ variable, so you type .=flip. If you only have .flip, you only reverses the string, but the result is not used and the original line is printed.

An equivalent program with .flip and with no -p looks like this:

$ raku -ne'.flip.say' data.txt

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Using command-line options

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