latex Basic definition of macros


Define a new basic command

A macro can be defined using \newcommand. For example:

\newcommand{\foo}{Just foo, you see?}

defines a macro \foo that expands to Just foo, you see?. It can then be used like any built-in command, for example after that definition:

He said: ``\foo''

expands to

He said: ``Just foo, you see?''

Define a new command with arguments

Macros can also have arguments. The number of arguments is given as optional argument between the command name and the replacement text. In the replacement text, the arguments are accessed with #1, #2 etc. For example:

\newcommand{\better}[2]{A #1 is better than a #2.}
\better{solution}{problem} % gives: A solution is better than a problem

Redefining an existing command

If a macro has already been defined, \newcommand gives an error. To give a new definition for an existing command, \renewcommand is used instead. Other than the different name, the syntax is exactly the same. For example, after the definition of \foo above, one could use:

\renewcommand{\foo}{Another foo, please.}

After that redefinition, the macro \foo no longer expands to Just foo, you see? but to Another foo, please.