The foreach command will execute another command against every item in an incoming list. The list can be passed directly or piped into this command. The default delimiter is a new line so this works great piping the output of file listings directly in, which have a file name per line.
This powerful construct allows you to perform basic loops from the CLI over arbitrary input. Most of the examples show file listings, but any input can be used that you want to iterate over.
This example will use the echo command to output each filename returned by ls. The echo is called once for every line of output being piped in.
The default command is "echo" but you can perform an action against the incoming list of items. This example will use "cat" to output the contents of each file in the incoming list.
You can customize the delimiter. This example passes a hard-coded input and spits it on commas. So here, the install command is run three times, once for each package. A contrived, but effective example.
If you want a more complex command, you can choose exactly where you wish to use the incoming item by referencing the default system setting expansion of ${item}. Remember to escape the expansion in your command so it's resolution is deferred until the forEach runs it internally. Here we echo each file name followed by the contents of the file.
You may also choose a custom placeholder name for readability.
The forEach can also iterate over JSON representations of objects or arrays. This means you can pipe in JSON from a file, a command such as package show or any REPL operation that returns complex data. The delimiter parameter is ignored for JSON input.
If iterating over an array, each item in the array will be available as ${item}. If iterating over a object, the object keys will be in ${item} and the values will be in ${value}. You can customize the system setting name for value with the valueName parameter to forEach.