Guide to LaTeX (4th Edition) (Tools and Techniques

194 Chapter 8. User Customizations
Testing text
To test if two commands evaluate to the same piece of text, or if a
command is defined as a certain string of text, use
\equal{string1}{string2}
where string1 and string2 are texts or commands that reduce to text. For
example, with
\ifthenelse {\equal{\name}{Fred}} {Frederick} {??}
the text Frederick is inserted if \name has been defined to be Fred (with
\newcommand), otherwise two question marks are printed.
Testing lengths
Another logical statement compares two lengths.
\lengthtest{relation}
where relation consists of two lengths or length commands separated by
a relational operator . For example,
\newlength{\horiz} \newlength{\vert}
\newlength{\min}
. . . . . . .
\ifthenelse {\lengthtest{\horiz > \vert}}
{\setlength{\min}{\vert}} {\setlength{\min}{\horiz}
sets \min to be the smaller of \horiz and \vert.
Testing switches
A boolean switch is a parameter that is either 〈true〉 or 〈false〉, also called
a flag. Three commands exist to handle them:
\newboolean{string} creates a new switch
\setboolean{string}{value} assigns a value true or false
\boolean{string} tests its value
The last of these is used as test in \ifthenelse and \whiledo.
There are a number of internal L AT E X switches that may also be tested
(but never reset!). The most useful of these are @twoside and @twocolumn
for checking if two-side or two-column modes are active. Since they
contain the character @, they may only be used inside a class or package
file (Appendix D).