> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/perl6-rosettacode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/perl6-rosettacode/programming_tasks/u/update_a_configuration_file.md).

# Update a configuration file

Implemented as a command-line script which can make arbitrary in-place updates to such config files.

Assuming that the script is saved as `conf-update` and the config file as `test.cfg`, the four changes required by the task description could be performed with the command:

```
conf-update --/needspeeling --seedsremoved --numberofbananas=1024 --numberofstrawberries=62000 test.cfg
```

The script:

```perl
use File::Temp;

my ($tmpfile, $out) = tempfile;

sub MAIN ($file, *%changes) {
    %changes.=map({; .key.uc => .value });
    my %seen;

    for $file.IO.lines {
        when /:s ^ ('#' .* | '') $/ {
            say $out: ~$0;
        }
        when /:s ^ (';'+)? [(\w+) (\w+)?]? $/ {
            next if !$1 or %seen{$1.uc}++;
            my $new = %changes{$1.uc}:delete;
            say $out: format-line $1, |( !defined($new)  ?? ($2, !$0)  !!
                                         $new ~~ Bool    ?? ($2, $new) !! ($new, True) );
        }
        default {
            note "Malformed line: $_\nAborting.";
            exit 1;
        }
    }

    say $out: format-line .key, |(.value ~~ Bool ?? (Nil, .value) !! (.value, True))
        for %changes;

    $out.close;

    copy $tmpfile, $file;
}

sub format-line ($key, $value, $enabled) {
    ("; " if !$enabled) ~ $key.uc ~ (" $value" if defined $value);
}
```