Raku Books / Raku One-Liners / Working with Files

Renaming files

Let us solve a task to rename all the files passed in the command-line arguments and give the files sequential numbers in the preferred format. Here is an example of the command line:

$ raku rename.raku *.jpg img_0000.jpg

In this example, all image files in the current directory will be renamed to img_0001.jpg, img_0002.jpg, etc.

And here’s the possible solution in Raku (save it in rename.raku):

@*ARGS[0..*-2].sort.map: *.Str.IO.rename(++@*ARGS[*-1])

🖥 This program reads the local environment (files, directories, or the command line), so it runs on your own computer but not in the sandboxed in-browser engine.

The pre-defined dynamic variable @*ARGS contains the arguments from the command line. In the above example, the shell unrolls the *.jpg mask to a list of files, so the array contains them all. The last element is the renaming sample img_0000.jpg.

If you are familiar with C or Perl, notice that the variable is called ARGS, not

ARGV.

To loop over all the files (and skipping the last file item with the file mask), we are taking the slice of @*ARGS. The 0..*-2 construct creates a range of indices to take all elements except the last one.

Then, the list is sorted (the original @*ARGS array stays unchanged), and we iterate over the file names using the map method.

The body of map contains a WhateveCode block (see Chapter 6); it takes the string representation of the current value, makes an IO::Path object out of it, and calls the rename method. Notice that the IO method creates an object of the IO::Path class; while a bare IO is a role in the hierarchy of the Raku object system.

Finally, the increment operator ++ changes the renaming sample (which is held in the last, *-1st, element of @*ARGS). When the operator is applied to a string, it increments the numeric part of it, so we get img_0001.jpg, img_0002.jpg, etc.

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