Competencies: CLI & Terminal > Shell & Scripting

Bash Fundamentals

Variables, quoting rules, command substitution, arithmetic, exit codes, positional parameters, special variables ($?, $$, $!).

Critical

All Engineering

POSIX Shell Compatibility

Portable shell scripting, POSIX vs bashisms, /bin/sh considerations, compatibility testing, shellcheck.

High

DevOps, Systems Administrator, SRE

Conditionals and Loops

if/elif/else, case statements, for/while/until loops, break/continue, test operators ([[ ]] vs [ ]).

Critical

All Engineering

Parameter Expansion

Default values (${var:-default}), pattern removal (${var##pattern}), substring, array slicing, indirect expansion.

High

Shell Developer, Automation, DevOps

Arrays and Associative Arrays

Indexed arrays, associative arrays (declare -A), array operations, iteration patterns, bash 4+ features.

High

Shell Developer, DevOps, SRE

Pipes and Composition

Unix philosophy, pipeline construction, avoiding UUOC, tee for splitting, process substitution <(cmd).

Critical

All Engineering

Here Documents

Heredocs for multi-line strings, variable expansion control ('EOF' vs EOF), indentation handling, here-strings.

High

All Engineering

Functions

Function definition, local variables, return values, recursion, function libraries, sourcing files.

High

Shell Developer, DevOps

Signal Handling

trap command, signal names, cleanup on exit, interrupt handling, graceful shutdown patterns.

Medium

Shell Developer, SRE

Error Handling

set -e/-u/-o pipefail, error checking patterns, logging, exit codes, errexit pitfalls.

High

DevOps, SRE, Shell Developer

Input/Output Redirection

stdin/stdout/stderr, file descriptors, redirection operators, here-documents, process substitution.

Critical

All Engineering

Zsh Features

Extended globbing, array syntax differences, prompt customization, completion system, oh-my-zsh.

Medium

Shell Developer, Power User

Pipes / Composition

Advanced

Multi-stage pipelines (cmd1 | cmd2 | cmd3); avoid UUOC; reduce pipe stages (grep+awk = just awk); tee for stream splitting

CLI Mastery Path

No named pipes (FIFOs) for complex IPC, no coproc

Process Substitution

Advanced

diff <(cmd1) <(cmd2), paste file <(cmd); treat command output as file without temp files; used for comparing config states

Bash Reference

No complex process substitution chains, still reaching for temp files occasionally

Parameter Expansion

Advanced

${var:-default}, ${var##pattern}, ${var%%pattern}, ${#var}, ${var/old/new}; array slicing; used in shell scripts for string manipulation without external tools

Bash Reference

No indirect expansion (${!var}), no namerefs in scripts

Heredocs

Advanced

Heredoc commits (gach/gacp), multi-line config generation, EOF with variable expansion control ('EOF' vs EOF); daily workflow for git commits

Bash Reference, Git Reference

Fully comfortable — no significant gaps