70 lines
3.0 KiB
Markdown
70 lines
3.0 KiB
Markdown
---
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title: Measuring Command Robustness
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TARGET DECK: Obsidian::STEM
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FILE TAGS: bash
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tags:
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- bash
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- shell
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---
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## 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.
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%%ANKI
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Basic
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What is a self-contained shell script?
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Back: A shell script that does not rely on the presence of other files.
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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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<!--ID: 1706726911473-->
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END%%
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%%ANKI
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Basic
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What makes a self-contained shell script more reliable?
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Back: There are no other files to misplace.
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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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<!--ID: 1706726911475-->
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END%%
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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
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$ awk 'program' input-file1 input-file2 ...
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$ awk -f program-file input-file1 input-file2 ...
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```
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It's interesting to think what else can be used as a measure of a command's robustness:
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* Required environment variables or environment variables formatted in a certain way
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* `$PATH` needs to point to a specific location
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* Whether the invoked program is present by default in a distribution or must be installed
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* The ability to run with or without an associated TTY
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* The ability to run with or without associated standard streams
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* `stdout`, `stderr`, `stdin`
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* How backwards compatible the invoked program is
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* Version mismatch may silently cause the same invocation to fail
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* Expected permissions
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* EUID, read permissions on an input file, etc.
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* Determinism of the program itself
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* Does output rely entirely on input or can it make nondeterministic choices
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* The amount of resources dedicated to the program
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* Failure may occur if not enough memory is provided to the command
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* Whether a program acts idempotently
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* What happens if I run the command twice in a row?
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* Whether a program acts atomically
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* Is it possible intermediate files are left that affect subsequent runs?
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* The presence of timeouts
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* Perhaps a program waits a specified amount of time before input is available. The command's success is now externally determined.
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* 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.
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The above scenarios are what makes something like [[nix/index|nix]] so compelling.
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## References
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* 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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