PIPELN: A pipeline creation tool

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Motivation

Executing programs from other programs to handle a specific task appeals to the UNIX philosophy of limiting the scope of individual programs, and using divide-and-conquer to tackle large, complex problems. Counter-intuitively, however, creating pipelines is only convenient in shell scripts.

Orchestrating pipelines from native binaries typically involves passing a command line (originating from the REPL nature of shells) to a shell via -c CMD. This forces the caller to glob command arguments together to a single string. Furthermore, the user input must now be sanitized to prevent unintended behavior, such as command injection. pipeln addresses this issue.

Features

Instead of parsing the pipeline definition from a single arg, pipeln uses the entire argument list it is invoked with, making it trivial to reason about how many and what arguments each invoked program will receive. The only input validation required by the caller is to ensure that "|" is not included in user-controlled arguments.

The program fits inside a single, small C file (~140 LOC).

The source code is available at https://git.sinitax.com/sinitax/pipeln.

Examples

Creating a pipeline using Python to find files that match a regular expression in the current directory:

#!/usr/bin/env python3

from subprocess import call
from sys import argv, exit

if len(argv) != 2 or argv[1] == "|":
    exit(1)

call(["pipeln", "find", "|", "grep", "-e", argv[1]])