Measuring Command Robustness

Overview

An interesting point Robbins discusses in his introduction to gawk is this idea of command robustness. He states that:

A self-contained shell script is more reliable because there are no other files to misplace.

He argues that the first command below is more robust than the second since the command is more loosely coupled to its environment:

$ awk 'program' input-file1 input-file2 ...
$ awk -f program-file input-file1 input-file2 ...

It’s interesting to think what else can be used as a measure of a command’s robustness:

• Required environment variables or environment variables formatted in a certain way
  • $PATH needs to point to a specific location
• Whether the invoked program is present by default in a distribution or must be installed
• The ability to run with or without an associated TTY
• The ability to run with or without associated standard streams
  • stdout, stderr, stdin
• How backwards compatible the invoked program is
  • Version mismatch may silently cause the same invocation to fail
• Expected permissions
  • EUID, read permissions on an input file, etc.
• Determinism of the program itself
  • Does output rely entirely on input or can it make nondeterministic choices
• The amount of resources dedicated to the program
  • Failure may occur if not enough memory is provided to the command
• Whether a program acts idempotently
  • What happens if I run the command twice in a row?
• Whether a program acts atomically
  • Is it possible intermediate files are left that affect subsequent runs?
• The presence of timeouts
  • Perhaps a program waits a specified amount of time before input is available. The command’s success is now externally determined.
• Locale-aware functionality
  • Consider for instance gawk’s \u sequence which targets characters in the current locale’s character set as opposed to specifically Unicode.
  • POSIX standard character classes serve as another example.

The above scenarios are what makes something like nix so compelling.

Bibliography

• Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. https://www.gnu.org/software/gawk/manual/gawk.pdf