Return to tt12 CVS log

Up to [CSRG BSD Unix] / 43BSDReno / share / doc / usd / 25.trofftut

Annotation of 43BSDReno/share/doc/usd/25.trofftut/tt12, revision 1.1

1.1     ! root        1: .\"    @(#)tt12        6.1 (Berkeley) 5/23/86
        !             2: .\"
        !             3: .NH
        !             4: Conditionals
        !             5: .PP
        !             6: Suppose we want the
        !             7: .BD .SH
        !             8: macro to leave two extra inches of space just before section 1,
        !             9: but nowhere else.
        !            10: The cleanest way to do that is to test inside the
        !            11: .BD .SH
        !            12: macro
        !            13: whether
        !            14: the section number is 1,
        !            15: and add some space if it is.
        !            16: The
        !            17: .BD .if
        !            18: command provides the conditional test
        !            19: that we can add
        !            20: just before the heading line is output:
        !            21: .P1 4
        !            22: ^if \e\en(SH=1 ^sp 2i  \e" first section only
        !            23: .P2
        !            24: .PP
        !            25: The condition after the
        !            26: .BD .if
        !            27: can be any arithmetic or logical expression.
        !            28: If the condition is logically true, or arithmetically greater than zero,
        !            29: the rest of the line is treated as if
        !            30: it were text _
        !            31: here a command.
        !            32: If the condition is false, or zero or negative,
        !            33: the rest of the line is skipped.
        !            34: .PP
        !            35: It is possible to do more than one command if a condition is true.
        !            36: Suppose several operations are to be done before section 1.
        !            37: One possibility is to define a macro 
        !            38: .BD .S1
        !            39: and invoke it
        !            40: if we are about to do section 1
        !            41: (as determined by an
        !            42: .BD .if ).
        !            43: .P1
        !            44: ^de S1
        !            45: ---  processing for section 1 ---
        !            46: ^^
        !            47: ^de SH
        !            48: ^^^
        !            49: ^if \e\en(SH=1 ^S1
        !            50: ^^^
        !            51: ^^
        !            52: .P2
        !            53: .PP
        !            54: An alternate way is to use the
        !            55: extended form of the
        !            56: .BD .if ,
        !            57: like this:
        !            58: .P1
        !            59: ^if \e\en(SH=1 \e{--- processing
        !            60: for section 1 ----\e}
        !            61: .P2
        !            62: The braces
        !            63: .BD \e{
        !            64: and
        !            65: .BD \e}
        !            66: must occur in the positions shown
        !            67: or you will get unexpected extra lines in your output.
        !            68: .UL troff
        !            69: also provides
        !            70: an `if-else' construction,
        !            71: which we will not go into here.
        !            72: .PP
        !            73: A condition can be negated by preceding it with
        !            74: .BD ! ;
        !            75: we get the same effect as above (but less clearly) by using
        !            76: .P1
        !            77: ^if !\e\en(SH>1 ^S1
        !            78: .P2
        !            79: .PP
        !            80: There are a handful of 
        !            81: other conditions that can be tested with
        !            82: .BD .if .
        !            83: For example, is the current page even or odd?
        !            84: .P1
        !            85: ^if o ^tl 'odd page title''- % -'
        !            86: ^if e ^tl '- % -''even page title'
        !            87: .P2
        !            88: gives facing pages different titles and page numbers on the
        !            89: outside edge when used inside an appropriate new page macro.
        !            90: .PP
        !            91: Two other conditions
        !            92: are
        !            93: .BD t
        !            94: and
        !            95: .BD n ,
        !            96: which tell you whether the formatter is
        !            97: .UL troff
        !            98: or
        !            99: .UL nroff . 
        !           100: .P1
        !           101: ^if t troff stuff ...
        !           102: ^if n nroff stuff ...
        !           103: .P2
        !           104: .PP
        !           105: Finally, string comparisons may be made in an
        !           106: .BD .if :
        !           107: .P1
        !           108: ^if  'string1'string2'  stuff
        !           109: .P2
        !           110: does `stuff' if
        !           111: .ul
        !           112: string1
        !           113: is the same as
        !           114: .ul
        !           115: string2.
        !           116: The character separating the strings can be anything
        !           117: reasonable that is
        !           118: not contained in either string.
        !           119: The strings themselves can reference strings with
        !           120: .BD \e* ,
        !           121: arguments with 
        !           122: .BD \e$ ,
        !           123: and so on.

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.