8e978fef9d
New: gotchas-skills.md (non-ASCII frontmatter, per-profile skill dirs). Updated: gotchas-bash.md (+((var++)) with zero), decisions.md (+python3 for JSON), process-lessons.md (+cat -A diagnostic). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
26 lines
1.8 KiB
Markdown
26 lines
1.8 KiB
Markdown
# Bash Gotchas
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## `set -e` silently kills scripts with complex subshell pipelines
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`set -euo pipefail` can cause silent termination with no output when scripts use loops containing command substitutions, subshell calls, and pipelines. The script appears to produce no output and exits non-zero. For read-only/reporting tools, use `set -uo pipefail` without `-e` and handle errors explicitly.
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## `grep` interprets option-like strings as flags
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`grep -qF "$var"` will fail if `$var` starts with `--` (e.g., `--dryrun`). Always use `--` to terminate option parsing: `grep -qF -- "$var"`.
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## `local` keyword only works inside functions
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Using `local` in the main script body (e.g., inside a `for` loop that isn't wrapped in a function) causes `local: can only be used in a function`. Either wrap the loop in a function or omit `local`.
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## `set -e` kills command substitution capturing non-zero exit codes
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`output=$(cmd)` where `cmd` exits non-zero will trigger `errexit` before `rc=$?` on the next line executes. Use `output=$(cmd) && rc=$? || rc=$?` or `output=$(cmd) || true` to safely capture output from commands expected to fail.
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## `((var++))` with var=0 triggers `set -e` exit
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Arithmetic expressions like `((PASS++))` return the *pre-increment* value. When PASS=0, the result is 0 (falsy), which `set -e` treats as a failure and silently exits the script. Use `PASS=$((PASS + 1))` instead — assignments always succeed regardless of the computed value.
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## `file` command marks shell scripts as "executable"
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The `file` command returns strings like "Bourne-Again shell script, Unicode text, UTF-8 text executable" for shell scripts. Grepping for `executable` to detect binaries will false-positive on text scripts. Instead, grep for `binary|image|archive` and additionally check that the output does NOT contain `text`.
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