# Linux Bash Scripting

> >-

- **Type:** Skill
- **Install:** `agentstack add skill-iliaal-whetstone-linux-bash-scripting`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [iliaal](https://agentstack.voostack.com/s/iliaal)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [iliaal](https://github.com/iliaal)
- **Source:** https://github.com/iliaal/whetstone/tree/master/distillery/generated-skills/linux-bash-scripting

## Install

```sh
agentstack add skill-iliaal-whetstone-linux-bash-scripting
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Linux Bash Scripting

Target: GNU Bash 4.4+ on Linux. No macOS/BSD workarounds, no Windows paths, no POSIX-only restrictions.

## Script Foundation

```bash
#!/usr/bin/env bash
set -Eeuo pipefail
shopt -s inherit_errexit

readonly SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"

trap 'printf "Error at %s:%d\n" "${BASH_SOURCE[0]}" "$LINENO" >&2' ERR
trap 'rm -rf -- "${_tmpdir:-}"' EXIT
```

- `-E` propagates ERR traps into functions
- `inherit_errexit` propagates errexit into `$()`  command substitutions
- Always create temp dirs under the EXIT trap: `_tmpdir=$(mktemp -d)`

## Core Rules

- Quote every expansion: `"$var"`, `"$(cmd)"`, `"${array[@]}"`
- `local` for function variables, `local -r` for function constants, `readonly` for script constants
- `printf '%s\n'` over `echo` — predictable behavior, no flag interpretation
- `[[ ]]` for conditionals; `(( ))` for arithmetic; `$()` over backticks
- End options with `--`: `rm -rf -- "$path"`, `grep -- "$pattern" "$file"`
- Require env vars: `: "${VAR:?must be set}"`
- Never `eval` user input; build commands as arrays: `cmd=("grep" "--" "$pat" "$f"); "${cmd[@]}"`
- Separate `local` from assignment to preserve exit codes: `local val; val=$(cmd)`

## Safe Iteration

```bash
# NUL-delimited file processing
while IFS= read -r -d '' f; do
    process "$f"
done &2; exit 1 ;;
        *)            break ;;
    esac
done
```

## Production Patterns

**Dependency check:**
```bash
require() { command -v "$1" &>/dev/null || { printf 'Missing: %s\n' "$1" >&2; exit 1; }; }
require jq; require curl
```

**Dry-run wrapper:**
```bash
run() { if [[ "${DRY_RUN:-}" == "1" ]]; then printf '[dry] %s\n' "$*" >&2; else "$@"; fi; }
run cp "$src" "$dst"
```

**Atomic file write** — write to temp, rename into place:
```bash
atomic_write() { local tmp; tmp=$(mktemp); cat >"$tmp"; mv -- "$tmp" "$1"; }
generate_config | atomic_write /etc/app/config.yml
```

**Retry with backoff:**
```bash
retry() { local n=0 max=5 delay=1; until "$@"; do ((++n>=max)) && return 1; sleep $delay; ((delay*=2)); done; }
retry curl -fsSL "$url"
```

**Script locking** — prevent concurrent runs:
```bash
exec 9>/var/lock/"${0##*/}".lock
flock -n 9 || { printf 'Already running\n' >&2; exit 1; }
```

**Idempotent operations** — safe to rerun:
```bash
ensure_dir()  { [[ -d "$1" ]] || mkdir -p -- "$1"; }
ensure_link() { [[ -L "$2" ]] || ln -s -- "$1" "$2"; }
```

## Logging

```bash
log() { printf '[%s] [%s] %s\n' "$(date -Iseconds)" "$1" "${*:2}" >&2; }
info()  { log INFO "$@"; }
warn()  { log WARN "$@"; }
error() { log ERROR "$@"; }
die()   { error "$@"; exit 1; }
```

## Anti-Patterns

| Bad | Fix |
|-----|-----|
| `for f in $(ls)` | `for f in *; do` or `find -print0 \| while read` |
| `local x=$(cmd)` | `local x; x=$(cmd)` — preserves exit code |
| `echo "$data"` | `printf '%s\n' "$data"` |
| `cat file \| grep` | `grep pat file` |
| `kill -9 $pid` first | `kill "$pid"` first, `-9` as last resort |
| `cd dir; cmd` | `cd dir || exit 1` or subshell `(cd dir && cmd)` |

## Performance

- Parameter expansion over externals: `${path%/*}` not `dirname`, `${path##*/}` not `basename`, `${var//old/new}` not `sed`
- `(( ))` over `expr`; `[[ =~ ]]` over `echo | grep`
- Cache results: `val=$(cmd)` once, reuse `$val`
- `xargs -0 -P "$(nproc)"` for parallel work
- `declare -A map` for lookups instead of repeated grep

## Bash 4.4+ / 5.x

- `${var@Q}` shell-quoted, `${var@U}` uppercase, `${var@L}` lowercase
- `declare -n ref=varname` nameref for indirect access
- `wait -n` wait for any background job
- `$EPOCHSECONDS`, `$EPOCHREALTIME` — timestamps without forking `date`

## Linux-Specific

- `/proc/self/status`, `/proc/cpuinfo`, `/proc/meminfo` for system info
- `systemctl` for services; `journalctl -u svc` for logs
- GNU coreutils: `sed -i` (no `''`), `grep -P` (PCRE), `readlink -f`
- `timeout 30s cmd` to prevent hangs
- `flock` for script locking (see above)
- Package install: `apt-get install -y` / `dnf install -y` / `pacman -S --noconfirm`

## ShellCheck

Run `shellcheck --enable=all script.sh`. Key rules:
- **SC2155**: Separate declaration from assignment
- **SC2086**: Double-quote variables
- **SC2046**: Quote command substitutions
- **SC2164**: `cd dir || exit`
- **SC2327/SC2328**: Use `${BASH_REMATCH[n]}` not `$n` for regex captures

Pre-commit: `shellcheck *.sh && shfmt -i 2 -ci -d *.sh`

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [iliaal](https://github.com/iliaal)
- **Source:** [iliaal/whetstone](https://github.com/iliaal/whetstone)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** yes
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-iliaal-whetstone-linux-bash-scripting
- Seller: https://agentstack.voostack.com/s/iliaal
- Browse the marketplace: https://agentstack.voostack.com/browse

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