shell-mastery — Builtins

compgen -b
compgen -b | wc -l

type cd           # cd is a shell builtin
type ls           # ls is /usr/bin/ls (external)
type -a echo      # echo is a shell builtin AND /usr/bin/echo
command -v awk    # /usr/bin/awk (shows path for externals)

# Navigation & environment
cd, pwd, pushd, popd, dirs, export, unset, source (.), hash

# I/O
echo, printf, read, mapfile, readarray

# Flow control
if, for, while, until, case, select, break, continue, return

# Job control
bg, fg, jobs, wait, kill, disown, suspend

# String/test
test ([), [[ ]], (( ))

# History
history, fc, !!, !$, !^, !:n

# Misc power tools
eval, exec, trap, shift, set, shopt, declare, local, readonly

compgen -b              # builtins
compgen -k              # keywords (if, for, while, case)
compgen -a              # aliases
compgen -A function     # defined functions
compgen -c              # ALL commands (builtins + externals + aliases + functions)
compgen -c | wc -l      # total command count
compgen -v              # all variables
compgen -e              # exported variables
compgen -f              # files in current dir
compgen -d              # directories in current dir
compgen -W "start stop restart" -- "st"  # word completion matching "st"