Rand Stats




A command line utility to execute commands on filesystem changes.

The interface should be fairly familiar for users of reflex. See the examples section below for some possible ways to use it.


$ zef install App::Lorea


lorea [options] -- command [args]


    --all                    Include all normally ignored files
-c, --config     STRING      The path to a configuration file
    --help                   Display usage information
-R, --ignore     REGEX ...   A regular expression to ignore filenames
-r, --regex      REGEX ...   A regular expression to match filenames
-e, --sequential             Run commands sequentially from config file
-s, --start-service          Run command as a service
    --substitute STRING      Set the string to be used as placeholder
-v, --verbose                Print tracing information
    --version                Print the version of the command and compiler

Options marked with ... can be provided multiple times.

Values marked as REGEX must be compilable as Raku regular expressions.


When lorea is run, it will monitor your current directory, and any directories under it, for any file-system changes. When a file is changed or added, it will be matched against the patterns you've specified (see below for details about how the matching is done).

If the event matches, the command you've specified will be run, or restarted if you enabled the --start-service flag.

If the command you've specified includes the {} string, this will be replaced by the absolute path of the file that has changed. All instances of this placeholder string will be replaced. If you need to use the {} string for something else, you can specify a different placeholder string with the --substitute option.


Patterns to match can be specified to lorea with either --regex or --ignore. Both of these options take Raku regular expressions, with the difference that any match for the former will trigger an event, while every match for the latter will explicitly not trigger one.

Paths are normalised before being matched, and converted to paths relative to the current directory without a leading ./. Matching directories will have a trailing slash (/).

If no pattern is specified, all file-system changes will match.

Default ignores

By default, lorea ignores some common patterns to make it easier to use in most cases.

The --all option disables these defaults. This flag will take effect if set either at the top level, or in any of the watchers specified in the configuration file (see below).

You can see the global ignores by setting the --verbose option.


The --config option can be used to specify a configuration to use to start several watchers at the same time. The behaviour of these watchers can be set independently.

The format of this file is intentionally very limited. A valid file will look something like this:

# Rebuild SCSS when it changes
-r '\.scss$' -- \
   sh -c 'sass {} `basename {} .scss`.css'

# Restart server when ruby code changes
-s -r '\.rb$' -- \

Each line will be interpreted as the parameters to a separate invocation of lorea. Lines must not include the executable name (that will be filled in internally). The parameters to a single invocation can be broken into multiple lines if they end with a trailing backslash (\).

Empty lines, and lines beginning with a hash (#) will be ignored.

With the exception of --help , --sequential, and --config itself, all options are valid within a configuration file. If the --config option is set, the only other flags that are allowed at the top level are --verbose and --sequential.

Sequential execution

When using a config file to run multiple simultaneous commands, each of them will be started asynchronously whenever possible. This means that, while there will only be one instance of a particular command, two different commands may overlap. This is usually what you want.

As a concrete example, consider this config file:

-- sh -c 'for i in `seq 1 5`; do sleep 0.1; echo first; done'
-- sh -c 'for i in `seq 1 5`; do sleep 0.1; echo second; done'

When this runs, you might see something like this:


Note that, since both commands started at the same time, the output of both is interleaved. If this is not what you want, you can ensure only one command runs at a time with the --sequential flag used at the top-level (it is not allowed in config files). In this case, the output might instead look like this:


Note in this case that even when using --sequential there is no guarantee that the commands will be executed in the order they appear in the config file.


Part of what lorea does is apply some heuristics to batch together file changes. There are many reasons that files change on disk, and these changes frequently come in large bursts. For instance, when you save a file in your editor, it probably makes a tempfile and then copies it over the target, leading to several different changes. A more dramatic example will happen when you do a source-control checkout, in which case there is no limit to the number of files that might change at once.

If lorea did not batch these changes, this could lead to your computer slowing down to a crawl, or the whole process crashing.

There are two modes to batch these changes.

If your command is marked as a service, or has no placeholders in it, then lorea assumes that individual changes are not as important as the fact that a change took place. In this case changes will be collected, and a single command execution will trigger once a short amount of time has passed between them.

Otherwise, changes will be collected using the same logic as above, but every unique file change will trigger a separate execution of your command.


Every time a .raku or .rakumod file changes, print a string with the name of the modified file:

lorea --regex '\.raku(mod)?$' -- echo "Change in {}"

or the same thing, but taking advantage of Raku's regular expressions:

lorea --regex '".raku" [mod]? $' -- echo "Change in {}"

See Also