9.1.2 @code{sample-code}

Use the @code command to indicate text that is a piece of a program and which consists of entire syntactic tokens. Enclose the text in braces.

Thus, you should use @code for an expression in a program, for the name of a variable or function used in a program, or for a keyword in a programming language.

Use @code for command names in languages that resemble programming languages, such as Texinfo. For example, @code and @samp are produced by writing ‘@code{@@code}’ and ‘@code{@@samp}’ in the Texinfo source, respectively.

It is incorrect to alter the case of a word inside an @code command when it appears at the beginning of a sentence. Most computer languages are case sensitive. In C, for example, Printf is different from the identifier printf, and most likely is a misspelling of it. Even in languages which are not case sensitive, it is confusing to a human reader to see identifiers spelled in different ways. Pick one spelling and always use that. If you do not want to start a sentence with a command name written all in lower case, you should rearrange the sentence.

In the printed manual, @code causes TeX to typeset the argument in a typewriter face. In the Info file, it causes the Info formatting commands to use single quotation marks around the text. For example,

The function returns @code{nil}.

produces this:

The function returns nil.

Here are some cases for which it is preferable not to use @code:

• For shell command names such as ls (use @command).
• For shell options such as ‘-c’ when such options stand alone (use @option).
• Also, an entire shell command often looks better if written using @samp rather than @code. In this case, the rule is to choose the more pleasing format.
• For environment variable such as TEXINPUTS (use @env).
• For a string of characters shorter than a syntactic token. For example, if you are writing about ‘goto-ch’, which is just a part of the name for the goto-char Emacs Lisp function, you should use @samp.
• In general, when writing about the characters used in a token; for example, do not use @code when you are explaining what letters or printable symbols can be used in the names of functions. (Use @samp.) Also, you should not use @code to mark text that is considered input to programs unless the input is written in a language that is like a programming language. For example, you should not use @code for the keystroke commands of GNU Emacs (use @kbd instead) although you may use @code for the names of the Emacs Lisp functions that the keystroke commands invoke.

Since @command, @option, and @env were introduced relatively recently, it is acceptable to use @code or @samp for command names, options, and environment variables. The new commands allow you to express the markup more precisely, but there is no real harm in using the older commands, and of course the long-standing manuals do so.

Ordinarily, TeX will consider breaking lines at ‘-’ and ‘_’ characters within @code and related commands. This can be controlled with @allowcodebreaks (see section @allowcodebreaks).