Working in Bash on Unix Systems

A condensed field guide to getting things done in a POSIX shell.

1. Stringing Commands Together

The shell glues commands with a handful of operators. Pick the one that matches the relationship you want between steps.

2. Touching the Filesystem

3. Watching and Steering Processes

4. Reshaping Text

5. Environment Variables

6. Talking to the Network

7. A Starter Script

#!/usr/bin/env bash
set -euo pipefail   # stop on errors, unset vars, and broken pipes

# Resolve where this script lives, regardless of caller's cwd
here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# Tiny logging helpers
say()  { printf '\033[0;32m[ok]\033[0m %s\n' "$1"; }
warn() { printf '\033[0;31m[!!]\033[0m %s\n' "$1" >&2; }

run() {
    say "kicking off in $here"
    # real work goes here
    say "finished"
}

run "$@"

8. Patterns Worth Memorizing

Confirm a binary is present before using it:

if command -v docker >/dev/null 2>&1; then
    warn() { :; }   # docker exists, proceed
fi

Fall back to a default argument:

target="${1:-./build}"

Walk a file one line at a time:

while IFS= read -r entry; do
    printf 'got: %s\n' "$entry"
done < hosts.txt

Iterate over matching files:

for src in ./*.css; do
    printf 'minifying %s\n' "$src"
done

9. Coming from PowerShell?

The biggest mental shift: PowerShell pipes objects, Bash pipes raw bytes. Quote variables so word-splitting doesn't surprise you.

10. Failing Safely

Turn on guard rails at the top of any non-trivial script:

set -e          # bail on the first failing command
set -u          # treat unset variables as errors
set -o pipefail # a failure anywhere in a pipe fails the whole pipe
set -x          # echo each command (handy while debugging)

Guarantee cleanup even when something blows up:

workdir="$(mktemp -d)"
finish() { rm -rf "$workdir"; }
trap finish EXIT

Takeaway: chain with && when each step depends on the last, enable set -euo pipefail for safety, and always wrap variables in quotes.