Pipelines and Variables
Updated: Oct 25
Most interaction with marcel involves the execution of a pipeline. For example:
ls -fr | select (f: now() - f.mtime < days(1))
ls explores the current directory recursively (-r), returning only files (-f). The resulting File objects are piped to the select operator, which keeps only those that have changed in the past day.
You write a command like this, hit return, get your result. But you can also store a pipeline in a variable for later execution, much as you would when writing a function in any programming language.
To store the above command in a variable, use conventional assignment notation, putting the pipeline inside brackets:
recent = (| ls -fr | select (f: now() - f.mtime < days(1)) |)
You can run this command at any time by just using the variable as if it were an operator:
You can also parameterize a pipeline. For example, the following pipeline explores the current directory recursively, and locates files with a given extension, (e.g. .py in util.py):
ext = (| e: ls -fr | select (f: f.suffix == e) |)
You can now run this pipeline, providing the extension of interest either as an argument:
Or using flag notation, where the flag name is determined by the parameter's name:
exp -e .py