Wordsplitting: How Your Shell Splits Command-Line Arguments

The user’s shell splits the command-line string into words before passing them as command-line arguments to Python, which assigns them to sys.argv.

../_images/argument_parser.png
  1. sys.argv[0] contains the program name
  2. sys.arg[1:] contains the list of command-line arguments

Note

The interpretation of command-line arguments, including word-splitting is dependent on the shell; not every shell parses the command-line string the same way. Generically speaking however, it splits words at whitespaces and trims any left over whitespace from the ends.

Info on how shells/consoles parse command-line arguments:

If it’s not in the list you’ll need to manually search for documentation specific to your shell.

Quoting & Escape Characters

Quoting can be used to:

  • Disable special treatment for special characters.
  • To prevent reserved words from being recognized as such.
  • To prevent parameter expansion.
  • To protect multi-word arguments from word spliting.

Escape characters can be used to:

  • Disable special treatment for a single special character.

Bash provides two types of quoting:

  1. Weak quoting: double-quotes
  2. Strong quoting: single-quotes

Windows only allows double-quotes

You don’t necessarily need to understand the details of each shell, but if you support command-utilities and a it’s helpful to know how the shells parse the command string before it ever gets to your Python program.