16.1 Introduction

Command line arguments are available through the command-line function from the (rnrs programs (6)) library. For the purposes of this documentation, command line arguments are divided into three categories:

Option without value

A string selecting a configuration option that can be turned on or off. It can be a single character (brief option) or a full–word (long option).

Option with value

A string selecting a value for a configuration option; an option’s value is a string of any length, including the empty string.

Non–option

A value to be passed to the program.

Let’s assume that:

• -v, -i and -h are brief options that do not require a value.
• -f, -o and -I are brief options that do require a value.
• --verbose, --interactive and --help are long options that do not require a value.
• --file, --output and --include are long options that do require a value.

the following command line chunks are so interpreted:

-vh -o green -i -Iwhite -f red

The -v, -h and -i options without value; the -o option with value ‘green’; the -I option with value ‘white’; the -f option with value ‘red’.

--verbose --help --output=green --interactive

--include white --file=red

The --verbose, --help and --interactive options without value; the --output option with value ‘green’; the --include option with value ‘white’; the --file option with value ‘red’.

The argument -- is recognised as “end of options” marker: all the arguments following it are interpreted as non–options, even if their string starts with a dash or double dash.

Chains of brief options are allowed: the options -v, -i and -h can be selected with the single argument -vih. Notice, though, that only options with no value can be chained; an option with value can appear only as last in the train, with no value attached. For example:

-vihI white

is interpreted as the options -v, -i and -h with no value followed by the option -I with value ‘white’; the following:

-vihIwhite              ;forbidden

could be made possible but, being unreadable, it is forbidden.

Notice that a single dash, ‘-’, is a valid non–option argument.