notebook/notes/bash/robustness.md

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---
title: Measuring Command Robustness
TARGET DECK: Obsidian::STEM
FILE TAGS: bash
tags:
- bash
- shell
---
## Overview
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An interesting point Robbins discusses in his introduction to [[posix/awk/index|gawk]] is this idea of command robustness. He states that:
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> 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)
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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)
<!--ID: 1706726911475-->
END%%
He argues that the first command below is more robust than the second since the command is more loosely coupled to its environment:
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```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
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* 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.
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* 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.
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## Bibliography
* 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)