Automating with scripts.
WHAT A SCRIPT IS
A file of commands, run in sequence.
WHAT THE FIRST LINE SHOULD BE
A shebang naming the interpreter.
WHY
It ensures the script runs under the shell you wrote it for.
WHAT TO SET AT THE TOP OF ANY SERIOUS SCRIPT
Exit on error Exit on undefined variables Failure of any command in a pipeline
WHY THOSE THREE
Without them, a script continues after failures and produces wrong results silently.
WHAT VARIABLES LOOK LIKE
A name, an equals sign, no spaces around it.
HOW TO USE ONE
A dollar sign, and braces around the name.
WHY BRACES
They remove ambiguity when adjacent to other text.
WHAT TO ALWAYS DO WITH VARIABLES IN COMMANDS
Quote them.
WHY
Unquoted variables break on spaces and expand wildcards unexpectedly.
WHAT CONDITIONALS LOOK LIKE
if, a test, then, and fi.
WHAT TESTS ARE COMMON
Whether a file exists Whether a string is empty Numeric comparison
WHAT LOOPS LOOK LIKE
for over a list, or while on a condition.
WHAT EXIT CODES MEAN
Zero is success; anything else is failure.
WHAT TO RETURN
A non-zero code when your script fails.
WHY
Whatever runs it needs to know.
