The teTeX HOWTO: The Linux-teTeX Local Guide: LaTeX commands.

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## 4. LaTeX commands.

## 4.1 Document structure.

Documents formatted for LaTeX have a few more rules, but with complex documents, LaTeX can greatly simplify the formatting process.

Essentially, LaTeX is a document markup language which tries to separate the output style from the document's logical content. For example, formatting a section heading with TeX would require specifying 36 points of white space above the heading, then the heading itself set in bold, 24-point type, then copying the heading text and page number to the Table of Contents, then leaving 24 points of white space after the heading. By contrast, LaTeX has the `\section{}` command, which does all of the work for you. If you need to change the format of the section headings throughout your document, you can change the definition of `\section{}` instead of the text in the document. You can see where this would save hours of reformatting for documents of more than a dozen pages in length.

All LaTeX documents have three sections: a preamble, the body text, and a postamble. These terms are standard jargon and are widely used by TeXperts.

The preamble, at a minimum, specifies the type of document to be produced---the document class---and a statement which signals the beginning of the document's body text. For example:

    \documentclass{article}
    \begin{document}

The document's postamble is usually very simple. Except in specialized cases, it contains only the statement:

    \end{document}

Note the `\begin{document}` and `\end{document}` pairing. In LaTeX, this is called an environment. All text must appear within an environment, and many commands are effective only in the environments in which they're called. The `document` environment is the only instance where LaTeX enforces this convention, however. That is, it's the only environment that is required in a document. (An exception is `letter` class, which also requires you to declare `\begin{letter}` and `\end{letter}`. See the section Letters.) However, many formatting features are specified as environments. They're described in the following sections.

The document classes can be called with arguments. For example, instead of the default, 10-point type used as the base point size, as in the previous example, we could have specified

    \documentclass[12pt]{article}

to produce the document using 12 points as the base point size. The document class, article, makes the necessary adjustments.

There are a few document classes which are commonly used. They're described below. The report class is similar to article class, but produces a title page and starts each section on a new page. The letter class includes special definitions for addresses, salutations, and closings, a few of which are described below.

You can include canned LaTeX code, commonly known as a package, with the `\usepackage{}` command.

    \usepackage{fancyhdr}

The command above would include the LaTeX style file `fancyhdr.sty` from one of the `TEXINPUTS` directories, which you and teTeX specified during installation and setup processes.

    \documentclass{article}
    \usepackage{fancyhdr}
    \begin{document}

Note that the `\usepackage{}` declarations are given before the `\begin{document}` statement; that is, in the document preamble.

`fancyhdr.sty` extends the `\pagestyle{}` command so that you can create custom headers and footers. Most LaTeX document classes provide headers and footers of the following standard page styles:

    \pagestyle{plain}       % default pages style -- page number centered at
                            % the bottom of the page.
    \pagestyle{empty}       % no headers or footers
    \pagestyle{headings}    % print section number and page number at the
                            % top of the page.
    \pagestyle{myheadings}  % print custom information in the page heading.

Everything on a line to the right of the percent sign is a comment.

The `\pagestyle{}` command doesn't take effect until the following page. To change the headers and footers on the current page, use the command

    \thispagestyle{the_pagestyle}

## 4.2 Characters and type styles.

Character styles are partially a function of the fonts specified in the document. However, bold and italic character emphasis should be available for every font present on the system. Underlining, too, can be used, though its formatting presents special problems. See section LaTeX extension packages and other resources, below.

You can specify text to be emphasized in several ways. The most portable is the `\em` command. All text within its scope is italicized by default. For example:

    This word will be {\em emphasized.}

If you have italicized text that runs into text which is not italicized, you can specify an italic correction factor to be used. The command for this is `\/`; that is, a backslash and a forward slash.

    This example {\em will\/} print correctly.

    This example will {\em not} print correctly.

Slightly less portable, but still acceptable in situations where they're used singly, are the commands `\it`, `\bf`, and `\tt`, which specify that the characters within their scope be printed using italic, bold, and monospaced (teletype) typefaces, respectively.

    {\tt This text will be printed monospaced,}
    {\it this text will be italic,} and
    {\bf this text will be bold\dots} all in one paragraph.

The command `\dots` prints a series of three periods for ellipses, which will not break across a line.

The most recent version of LaTeX, which is what you have, includes commands which account for instances where one emphasis command would supersede another.

    This is {\it not {\bf bold italic!}}

What happens is that teTeX formats the text with the italic typeface until it encounters the `\bf` command, at which point it switches to boldface type.

To get around this, the NFSS scheme of selecting font shapes requires three parameters for each typeface: shape, series, and family. Not all font sets will include all of these styles. LaTeX will print a warning, however, if it needs to substitute another font.

You can specify the following font shapes:

    \textup{text}           % upright shape (the default)
    \textit{text}           % italic
    \textsl{text}           % slanted
    \textsc{text}           % small caps

These are the two series that most fonts have:

    \textmd{text}           % medium series (the default)
    \textbf{text}           % boldface series.

There are generally three families of type available.

    \textrm{text}           % Roman (the default)
    \textsf{text}           % sans serif
    \texttt{text}           % typewriter (monospaced, Courier-like)

Setting font styles using these parameters, you can combine effects.

    \texttt{\textit{This example likely will result in a font
    substitution, because many fonts don't include a typewriter italic
    typeface.}}

The font family defaults to Computer Modern, which is a bit-mapped font. Other font families are usually Postscript-format Type 1 fonts. See section Using PostScript fonts for details on how to specify them.

There are also many forms of accents and special characters which are available for typesetting. This is only a few of them. (Try typesetting these on your own printer.)

    \'{o}   \`{e}   \^{o}   \"{u}   \={o}   \c{c}   `? `!
    \copyright      \pounds         \dag

Finally, there are characters which are used as meta- or escape characters in TeX and LaTeX. One of them, the dollar sign, is mentioned above. The complete set of meta characters, which need to be escaped with a backslash to be used literally, is:

    # $ % & _ { }

There are also different alphabets available, like Greek and Cyrillic. LaTeX provides many facilities for setting non-English text, which are covered by some of the other references mentioned here

## 4.3 Margins and line spacing.

Changing margins in a TeX or LaTeX document is not a straightforward task. A lot depends on the relative indent of the text you're trying to adjust the margin for. The placement of the margin-changing command is also significant.

For document-wide changes to LaTeX documents, the `\evensidemargin` and `\oddsidemargin` commands are available. They affect the left-hand margins of the even-numbered and odd-numbered pages, respectively. For example,

    \evensidemargin=1in
    \oddsidemargin=1in

adds on inch to the left-hand margin of the even and odd pages in addition to the standard one-inch, left-hand margin. These commands affect the entire document and will shift the entire body of the text right and left across a page, regardless of any local indent, so they're safe to use with LaTeX environments like `verse` and `list`.

Below is a set of margin-changing macros which I wrote. They have a different effect than the commands mentioned above. Because they use plain TeX commands, they're not guaranteed to honor the margins of any LaTeX environments which may be in effect, but you can place them anywhere in a document and change the margins from that point on.

    %%  margins.sty -- v. 0.1   by Robert Kiesling
    %%  Copies of this code may be freely distributed in verbatim form.
    %%
    %%  Some elementary plain TeX margin-changing commands. Lengths are
    %%  in inches:
    %%  \leftmargin{1}   %% sets the document's left margin in 1 inch.
    %%  \leftindent{1}   %% sets the following paragraphs' indent in
    %%                     1 inch.
    %%  \rightindent{1}  %% sets the following paragraphs' right margins
    %%                   %% in 1 inch.
    %%  \llength{3}      %% sets the following lines' lengths to 3 inches.
    %%
    \message{Margins macros...}
    \def\lmargin#1{\hoffset = #1 in}
    \def\lindent#1{\leftskip = #1 in}
    \def\rindent#1{\rightskip = #1 in}
    \def\llength#1{\hsize = #1 in}
    %%
    %% (End of margins macros.}

Place this code in a file called `margins.sty` in your local `$TEXINPUTS` directory. The commands are explained in the commented section of the file. To include them in a document, use the command

    \usepackage{margins}

in the document preamble.

While we're on the subject, if you don't want the right margin to be justified, which is the default, you can tell LaTeX to use ragged right margins by giving the command:

    \raggedright

Setting line spacing also has its complexities.

The baselineskip measurement is the distance between lines of text. It is given as an absolute measurement. For example,

    \baselineskip=24pt

or even better:

    \setlength{\baselineskip}{24pt}

The difference between the two forms is that setlength will respect any scoping rules that may be in effect when you use the command.

The problem with using baselineskip is that it also affects the distance between section headings, footnotes, and the like. You need to take care that baselineskip is correct for whatever text elements you're formatting. There are, however, LaTeX macro packages, like `setspace.sty,` which will help you in these circumstances. See section LaTeX extension packages and other resources.

## 4.4 Document classes.

LaTeX provides document classes which provide standardized formats for documents. They provide environments to format lists, quotations, footnotes, and other text elements. Commonly used document classes are covered in the following sections.

### Articles and reports.

As mentioned above, the `article` class and the `report` class are similar. The main differences are that the report class creates a title page by default and begins each section on a new page. Mostly, though, the two document classes are similar.

To create titles, abstracts, and bylines in these document classes, you can type, for example,

    \title{The Breeding Habits of Cacti}
    \author{John Q. Public}
    \abstract{Description of how common desert cacti search
    for appropriate watering holes to perform their breeding
    rituals.}

in the document preamble. Then, the command

    \maketitle

given at the start of the text, will generate either a title page in the report class, or the title and abstract at the top of the first page, in the article class.

Sections can be defined with commands that include the following:

    \section
    \subsection
    \subsubsection

These commands will produce the standard, numbered sections used in technical documents. For unnumbered sections, use

    \section*
    \subsection*
    \subsubsection*

and so on.

LaTeX provides many environments for formatting displayed material. You can include quoted text with the `quotation` environment.

    \begin{quotation}
    Start of paragraph to be quoted...

    ... end of paragraph.
    \end{quotation}

For shorter quotes, you can use the `quote` environment.

To format verse, use the `verse` environment.

    \begin{verse}
    Because I could not stop for death\\
    He kindly stopped for me
    \end{verse}

Notice that you must use the double backslashes to break lines in the correct places. Otherwise, LaTeX fills the lines in a verse environment, just like any other environment.

Lists come in several flavors. To format a bulleted list, the `list` environment is used:

    \begin{list}
    \item
    This is the first item of the list.
    \item
    This is the second item of the list...
    \item
    ... and so on.
    \end{list}

A numbered list uses the `enumerate` environment:

    \begin{enumerate}
    \item
    Item No. 1.
    \item
    Item No. 2.
    \item
    \dots
    \end{enumerate}

A descriptive list uses the `description` environment.

    \begin{description}
    \item{Oven} Dirty, needs new burner.
    \item{Refrigerator}  Dirty.  Sorry.
    \item{Sink and drainboard}  Stained, drippy, cold water faucet.
    \end{description}

### Letters.

The `letter` class uses special definitions to format business letters.

The `letter` environment takes one argument, the address of the letter's addressee. The `address` command, which must appear in the document preamble, defines the return address. The `signature` command defines the sender's name as it appears after the closing.

The LaTeX source of a simple business letter might look like this.

    \documentclass[12pt]{letter}
    \signature{John Q. Public}
    \address{123 Main St.\\Los Angeles, CA.  96005\\Tel: 123/456-7890}
    \begin{document}
    \begin{letter}{ACME Brick Co.\\100 Ash St.\\San Diego, CA 96403}
    \opening{Dear Sir/Madam:}

    With regard to one of your bricks that I found on my living room
    carpet surrounded by shards of my broken front window...

    (Remainder of the body of the letter.)

    \closing{Sincerely,}

    \end{letter}
    \end{document}

Note that the addresses include double backslashes, which specify where the line breaks should occur.

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