LaTeX/Customizing LaTeX
From Wikibooks, the open-content textbooks collection
Documents produced with the commands you have learned up to this point will look acceptable to a large audience. While they are not fancy-looking, they obey all the established rules of good typesetting, which will make them easy to read and pleasant to look at. However, there are situations where LaTeX does not provide a command or environment that matches your needs, or the output produced by some existing command may not meet your requirements.
In this chapter, I will try to give some hints on how to teach LaTeX new tricks and how to make it produce output that looks different from what is provided by default.
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[edit] New commands
To add your own commands, use the
\newcommand{name}[num]{definition}
command. Basically, the command requires two arguments: the name of the command you want to create, and the definition of the command. The num argument in square brackets is optional and specifies the number of arguments the new command takes (up to 9 are possible). If missing it defaults to 0, i.e. no argument allowed.
The following two examples should help you to get the idea. The first example defines a new command called \wbal that will print "The Wikibook about LaTeX". Such a command could come in handy if you had to write the title of this book over and over again.
\newcommand{\wbal}{The Wikibook about LaTeX} This is ‘‘\wbal'' \ldots{} ‘‘\wbal'' |
This is “The Wikibook about LaTeX” … “The Wikibook about LaTeX” |
The next example illustrates how to define a new command that takes one argument. The #1 tag gets replaced by the argument you specify. If you wanted to use more than one argument, use #2 and so on, these arguments are added in an extra set of brackets.
\newcommand{\wbalsup}[1] {This is the Wikibook about LaTeX supported by #1} \newcommand{\wbalTwo}[2] {This is the Wikibook about LaTeX supported by #1 #2} % in the document body: \begin{itemize} \item \wbalsup{Wikimedia} \item \wbalsup{lots of users!} \item \wbalTwo{John}{Doe} \end{itemize} |
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LaTeX will not allow you to create a new command that would overwrite an existing one. But there is a special command in case you explicitly want this: \renewcommand. It uses the same syntax as the \newcommand command.
In certain cases you might also want to use the \providecommand command. It works like \newcommand, but if the command is already defined, LaTeX will silently ignore it.
With LaTex2e, it is also possible to add a default parameter to a command with the following syntax:
\newcommand{name}[num][default]{definition}
If the default parameter of \newcommand is present, then the first of the number of arguments specified by num is optional with a default value of default; if absent, then all of the arguments are required.
\newcommand{\wbalTwo}[2][Wikimedia]{This is the Wikibook about LaTeX supported by {#1} and {#2}!} % in the document body: \begin{itemize} \item \wbalTwo{John Doe} \item \wbalTwo[a lots of users]{John Doe} \end{itemize} |
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NOTE: when the command is used with an explicit first parameter it is given enclosed with brackets ( "[a lots of users]" ).
[edit] New Environments
Just as with the \newcommand command, there is a command to create your own environments. The \newenvironment command uses the following syntax:
\newenvironment{name}[num]{before}{after}
Again \newenvironment can have an optional argument. The material specified in the before argument is processed before the text in the environment gets processed. The material in the after argument gets processed when the \end{name} command is encountered.
The num argument is used the same way as in the \newcommand command. LaTeX makes sure that you do not define an environment that already exists. If you ever want to change an existing command, you can use the \renewenvironment command. It uses the same syntax as the \newenvironment command.
The example below illustrates the usage of the \newenvironment command:
\newenvironment{king} {\rule{1ex}{1ex}\hspace{\stretch{1}}} {\hspace{\stretch{1}}\rule{1ex}{1ex}} \begin{king} My humble subjects \ldots \end{king} |
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[edit] Extra space
When creating a new environment you may easily get bitten by extra spaces creeping in, which can potentially have fatal effects. For example when you want to create a title environment which suppresses its own indentation as well as the one on the following paragraph. The \ignorespaces command in the begin block of the environment will make it ignore any space after executing the begin block. The end block is a bit more tricky as special processing occurs at the end of an environment. With the \ignorespacesafterend LaTeX will issue an \ignorespaces after the special ‘end’ processing has occurred.
\newenvironment{simple}% {\noindent}% {\par\noindent} \begin{simple} See the space\\to the left. \end{simple} Same\\here. |
See the space to the left. Same here. |
\newenvironment{correct}% {\noindent\ignorespaces}% {\par\noindent% \ignorespacesafterend} \begin{correct} No space\\to the left. \end{correct} Same\\here. |
No space to the left. Same here. |
[edit] Command-line LaTeX
If you work on a Unix-like OS, you might be using Makefiles or any kind of script to build your LaTeX projects. In that connection it might be interesting to produce different versions of the same document by calling LaTeX with command-line parameters. If you add the following structure to your document:
\usepackage{ifthen} \ifthenelse{\equal{\blackandwhite}{true}}{ % "black and white" mode; do something.. }{ % "color" mode; do something different.. }
Now you can call LaTeX like this:
latex '\newcommand{\blackandwhite}{true}\input{test.tex}'
First the command \blackandwhite gets defined and then the actual file is read with input. By setting \blackandwhite to false the color version of the document would be produced.
[edit] Creating your own package
If you define a lot of new environments and commands, the preamble of your document will get quite long. In this situation, it is a good idea to create a LaTeX package containing all your command and environment definitions. You can then use the \usepackage command to make the package available in your document. Writing a package basically consists of copying the contents of your document preamble into a separate file with a name ending in .sty.
It is very simple, just follow the steps:
- create a simple text file called mypack.sty (or any other name you like) and open it with any text editor
- at the very beginning of the text document just write
\ProvidesPackage{mypack}
- note: it has to have the same name of the file without the extension. It tells LaTeX the name of the package and will allow it to issue a sensible error message when you try to include a package twice.
- write whatever you want in it using all the LaTeX commands you know. Normally you should define new commands or import other packages.
- import your new package with the known command
\usepackage{mypack}
the file mypack.sty and the LaTeX source you are compiling must be in the same directory. It will be like that all you have written within your package were within the document itself.
See also:
[edit] Creating your own style
It is also possible to create your own style file. The process is similar to the creation of your own package, you can call your own style file in the preamble of any document by the command:
\documentclass{mystyle}
The name of the style file is then mystyle.cls and can be opened with any text editor. At the beginning of this file, the following line has to be provided:
\ProvidesClass{mystyle}
again, within the style files other files or packages are imported by the requirepackage command.
[edit] Spacing
[edit] Line Spacing
If you want to use larger inter-line spacing in a document, you can change its value by putting the
\linespread{factor}
command into the preamble of your document. Use \linespread{1.3} for "one and a half" line spacing, and \linespread{1.6} for "double" line spacing. Normally the lines are not spread, so the default line spread factor is 1.
The setspace package allows more fine-grained control over line spacing. To set "one and a half" line spacing document-wide, but not where it is usually unnecessary (e.g. footnotes, captions):
\usepackage{setspace} %\singlespacing \onehalfspacing %\doublespacing %\setstretch{1.1}
To change line spacing within the document, the setspace package provides the environments singlespace, onehalfspace, doublespace and spacing:
This paragraph has \\ default \\ line spacing. \begin{doublespace} This paragraph has \\ double \\ line spacing. \end{doublespace} \begin{spacing}{2.5} This paragraph has \\ huge gaps \\ between lines. \end{spacing}
[edit] Paragraph formatting
In LaTeX, there are two parameters influencing paragraph layout. By placing a definition like:
\setlength{\parindent}{0pt} \setlength{\parskip}{1ex plus 0.5ex minus 0.2ex}
in the preamble of the input file, you can change the layout of paragraphs. These two commands increase the space between two paragraphs while setting the paragraph indent to zero.
The plus and minus parts of the length above tell TeX that it can compress and expand the inter paragraph skip by the amount specified, if this is necessary to properly fit the paragraphs onto the page. In continental Europe, paragraphs are often separated by some space and not indented. But beware, this also has its effect on the table of contents. Its lines get spaced more loosely now as well. To avoid this, you might want to move the two commands from the preamble into your document to some place below the command \tableofcontents or to not use them at all, because you’ll find that most professional books use indenting and not spacing to separate paragraphs.
If you want to indent a paragraph that is not indented, you can use
\indent
at the beginning of the paragraph. Obviously, this will only have an effect when \parindent is not set to zero. If you want to indent the beginning of every section, you can use the indentfirst package, see the chapter about LaTeX/Packages for more information.
To create a non-indented paragraph, you can use
\noindent
as the first command of the paragraph. This might come in handy when you start a document with body text and not with a sectioning command.
[edit] Horizontal Space
LaTeX determines the spaces between words and sentences automatically. To add horizontal space, use:
\hspace{length}
If such a space should be kept even if it falls at the end or the start of a line, use \hspace* instead of \hspace. The length in the simplest case is just a number plus a unit, e.g. \hspace{1.5 cm}. For a list of the possible units, see the Useful Measurement Macros appendix.
The command:
\stretch{n}
generates a special rubber space. It stretches until all the remaining space on a line is filled up. If two \hspace{\stretch{n}} commands are issued on the same line, they grow according to the stretch factor.
x\hspace{\stretch{1}} x\hspace{\stretch{3}} x |
x x x |
[edit] Vertical Space
The space between paragraphs, sections, subsections, etc. is determined automatically by LATEX. If necessary, additional vertical space between two paragraphs can be added with the command:
\vspace{length}
This command should normally be used between two empty lines. If the space should be preserved at the top or at the bottom of a page, use the starred version of the command, \vspace*, instead of \vspace. The \stretch command, in connection with \pagebreak, can be used to typeset text on the last line of a page, or to center text vertically on a page.
Additional space between two lines of the same paragraph or within a table is specified with the
\\[length]
command.
If you want to add space at the beginning of the document, without anything else written before, then you may use
{ \phantom{.} \vspace{length} }
It's important you use the \phantom command and the brackets, otherwise you'll get an error.
