As it is humanly impossible to memorize the syntax of hundreds of commands, most executable programs intended for command-line use provide a formal piece of documentation called a manual.

Although manual pages may vary in their format, they generally contain:

• The command's name and summary.
• A synopsis.
• A detailed description.
• A list of options.
• A list of exit statuses.

Here is for example, an excerpt of the echo command's manual page:

NAME     echo – write arguments to the standard outputSYNOPSIS     echo [-n] [string ...]DESCRIPTION     The echo utility writes any specified operands, separated by single blank (' ') characters     and followed by a newline ('\n') character, to the standard output.