Control Flow

Core Idea

Control flow is how a shell program chooses what happens next.

Without control flow, a script is just a fixed list of commands. With control flow, scripts can branch on success, repeat work, and stop when checks fail.

Main Tools

• Conditionals: choose a branch with if.
• Loops: repeat commands with for or while.
• Exit status: communicate success or failure.
• One-liners: combine control flow at the prompt when it stays readable.

Example

if [[ -f ~/src/pages/index.md ]]; then
  printf 'source exists\n'
else
  printf 'missing source\n' >&2
  exit 1
fi

Watch Out

Readable control flow beats clever control flow. If the command is hard to explain, make it a script with clear lines.

Docs Pointers

• Run help if, help for, and help while.
• Read if, for, while, and shell scripting.