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Script Checklist    -IAN! idallen@ncf.ca
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This is a list of things to verify in your shell scripts:

- script must start with a complete script header
  (interpreter, syntax, purpose, author, date, PATH, umask)

- validate script command line arguments before using them
  - validate correct number of arguments, correct type (numbers, files,
    pathnames, etc.), correct permissions (if a pathname)
  - issue warnings or errors if arguments are missing, extra arguments
    are present, or if arguments aren't valid

- validate any input received from the user via "read"
  - validate correct type (numbers, files, pathnames, etc.)
  - validate correct permissions (if a pathname)
  - issue warnings or errors if input isn't valid

- issue error messages on stderr (not stdout)
  - error messages must contain the script name as well as useful
    help on (a) exactly what was found and (b) what was expected
  - never say just "illegal input" or "invalid input" or "too many"
  - always specify how many is "too many" or "too few"
  - Example: "$0: Expecting 3 file names; found $# ($*)"

- issue prompts before reading input
  - prompt messages must appear on stderr so they don't get redirected
  - note: some menus might also be considered as prompts

- quote every use of a shell variable, and don't miss any
  - quote every use, every time, to prevent wildcard expansion
  - I mean every use, every time
  - I mean it
  - you might get away with not quoting $$, $#, and $?, but that's all
  - I *really* do mean it

- check the return codes of important commands in the script
  - minimal conditional checking syntax:  command || exit $?
  - no need to check "echo" commands that write to screen
  - pick the important commands (don't clutter the whole script)

- exit the script non-zero (bad status) when things go seriously wrong
  - don't keep processing bad data
  - exit if arguments are incorrect or not valid
  - exit if any important commands fail

- use good programming style
  - indent your code correctly inside control structures
    (basically the same rules as in C language)
  - avoid lines longer than 80 characters
    (break and continue long lines using a backslash to escape the newline)
  - add useful, helpful comments (not useless ones) in front of code blocks
    (don't comment in front of every single line)
  - use good variable names, related to your algorithm
    (don't copy the poor names used by your instructor in examples)
  - don't repeat code (parametrize your algorithm)

- test your scripts with problematic input
  - try wildcards, blanks, dashes, punctuation, empty strings, EOF, etc.
  - try no command line arguments and then hundreds of arguments
  - try short inputs, medium inputs, and huge long inputs
  - look for unquoted variables and put wildcards in them and watch
    your script blow up, then fix it by quoting all your variables
  - no input should cause a shell script to generate an internal error