Page 8 - Bash

Anyone who only checks WebSocket endpoints in the browser with DevTools loses reproducibility and automatability. With openssl, curl and websocat, you can test WebSocket connections with Bash, walk through the handshake by hand, and wire connection checks straight into the CI pipeline.

Shell scripts that inform the operator instead of confusing them are more maintainable, safer and more pleasant to use. With tput, ANSI codes, spinners, column and printf tables, professional CLI UX emerges without external dependencies, directly in Bash, portable and geared toward robustness.

Most developers know set -x only as a quick switch for more output and never use more than the default setting. With a customized PS4, targeted redirection of the trace output and selective switching on and off, set -x turns from a blunt tool into a precise Bash tracing technique that can also be safely used in CI pipelines.

sed, awk and perl can all solve text processing tasks in the shell, but each one brings different strengths, limits and performance characteristics. sed handles line based substitution, awk handles structured field processing, and perl covers complex logic, multiline patterns and Unicode. Picking the right tool saves time and avoids fragile solutions.

eval in Bash takes a concatenated string and evaluates it a second time as a shell command, and that is exactly the problem: any unvalidated input flowing into that string can inject arbitrary commands. This article walks through concrete attack scenarios involving eval and introduces safe alternatives such as arrays, namerefs, and printf minus v, which achieve the same dynamism without command injection.

A Bash script that calls curl, ssh or mysqldump cannot be meaningfully tested without touching real network connections or databases on every test run. Mocking external commands solves exactly this problem: the PATH override pattern and targeted function overriding make Bash tests deterministic, fast and independent of real infrastructure.

Shell scripts without tests are a black box in your automation. The Bash Automated Testing System (BATS) brings structured unit tests, fixtures, and mocking to the shell world, and it integrates seamlessly into GitHub Actions, GitLab CI, and Jenkins without any external runtime dependencies.

A migration runner ensures database schemas change traceably and in the right order across multiple environments. This article shows how to build a custom migration runner in Bash, with a tracking table, checksum verification, transactional execution, and a slim command line interface for up, down, and status.

Iterating over filenames that contain spaces is one of the most common mistakes in shell scripts. for f in $(find ...) breaks on spaces, tabs, and newlines in filenames. find -print0 with null byte separation, correct globbing, and read -d '' solve the problem once and for all: reliably, portably, and without special-case logic.

A raw diff output is technically complete but hard to read in a terminal, because lines marked with plus and minus barely stand out visually. This article shows how colored diff output emerges in Bash scripts, from ready-made tools like colordiff and git diff to your own ANSI coloring with awk for edge cases no standard tool covers.