--- title: Measuring Command Robustness TARGET DECK: Obsidian::STEM FILE TAGS: bash tags: - bash - shell --- ## Overview An interesting point Robbins discusses in his introduction to [[posix/awk/index|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. %%ANKI Basic What is a self-contained shell script? Back: A shell script that does not rely on the presence of other files. Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf) END%% %%ANKI Basic What makes a self-contained shell script more reliable? Back: There are no other files to misplace. Reference: Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf) END%% He argues that the first command below is more robust than the second since the command is more loosely coupled to its environment: ```bash $ 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 [[posix/awk/index|gawk]]'s `\u` [[escape-sequences|sequence]] which targets characters in the current locale's character set as opposed to specifically Unicode. * POSIX standard [[posix/regexp#Character Classes|character classes]] serve as another example. The above scenarios are what makes something like [[nix/index|nix]] so compelling. ## References * Robbins, Arnold D. “GAWK: Effective AWK Programming,” October 2023. [https://www.gnu.org/software/gawk/manual/gawk.pdf](https://www.gnu.org/software/gawk/manual/gawk.pdf)