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Annotation of 43BSDReno/share/doc/usd/12.edtut/e6, revision 1.1

1.1     ! root        1: .\"    @(#)e6  6.1 (Berkeley) 5/22/86
        !             2: .\"
        !             3: .SH
        !             4: Special Characters
        !             5: .PP
        !             6: You may have noticed that things just don't work right when you used
        !             7: some characters like
        !             8: \*.,
        !             9: .UL * ,
        !            10: .UL $ ,
        !            11: and others in
        !            12: context searches and the substitute command.
        !            13: The reason is rather complex, although the cure is simple.
        !            14: Basically,
        !            15: .ul
        !            16: ed
        !            17: treats these characters as special, with special meanings.
        !            18: For instance,
        !            19: .ul
        !            20: in a context search or the first string of the substitute command only,
        !            21: \*.
        !            22: means ``any character,'' not a period, so
        !            23: .P1
        !            24: /x\*.y/
        !            25: .P2
        !            26: means ``a line with an
        !            27: .UL x ,
        !            28: .ul
        !            29: any character,
        !            30: and a
        !            31: .UL y ,''
        !            32: .ul
        !            33: not
        !            34: just ``a line with an
        !            35: .UL x ,
        !            36: a period, and a
        !            37: .UL y .''
        !            38: A complete list of the special characters
        !            39: that can cause trouble is the following:
        !            40: .P1
        !            41: ^    \*.    $    [    *    \e
        !            42: .P2
        !            43: .ul
        !            44: Warning:
        !            45: The backslash character
        !            46: .UL \e
        !            47: is special to
        !            48: .ul
        !            49: ed.
        !            50: For safety's sake, 
        !            51: avoid it where possible.
        !            52: If you have to use one of the special characters
        !            53: in a substitute command,
        !            54: you can turn off its magic meaning temporarily
        !            55: by preceding it with the backslash.
        !            56: Thus
        !            57: .P1
        !            58: s/\e\e\e\*.\e*/backslash dot star/
        !            59: .P2
        !            60: will change
        !            61: .UL \e.*
        !            62: into ``backslash dot star''.
        !            63: .PP
        !            64: Here is a hurried synopsis of the other special characters.
        !            65: First, the circumflex
        !            66: .UL ^
        !            67: signifies
        !            68: the beginning of a line.
        !            69: Thus
        !            70: .P1
        !            71: /^string/
        !            72: .P2
        !            73: finds
        !            74: .UL string
        !            75: only if it is at the beginning of a line:
        !            76: it will find
        !            77: .P1
        !            78: string
        !            79: .P2
        !            80: but not
        !            81: .P1
        !            82: the string...
        !            83: .P2
        !            84: The dollar-sign
        !            85: .UL $
        !            86: is just the opposite of the circumflex;
        !            87: it means the end of a line:
        !            88: .P1
        !            89: /string$/
        !            90: .P2
        !            91: will only find an occurrence of
        !            92: .UL string
        !            93: that is at the end of some line.
        !            94: This implies, of course,
        !            95: that
        !            96: .P1
        !            97: /^string$/
        !            98: .P2
        !            99: will find only a line that contains just
        !           100: .UL string ,
        !           101: and
        !           102: .P1
        !           103: /^\*.$/
        !           104: .P2
        !           105: finds a line containing exactly one character.
        !           106: .PP
        !           107: The character
        !           108: .UL . ,
        !           109: as we mentioned above,
        !           110: matches anything;
        !           111: .P1
        !           112: /x\*.y/
        !           113: .P2
        !           114: matches any of
        !           115: .P1
        !           116: x+y
        !           117: x-y
        !           118: x y
        !           119: x\*.y
        !           120: .P2
        !           121: This is useful in conjunction with
        !           122: .UL * ,
        !           123: which is a repetition character;
        !           124: .UL a*
        !           125: is a shorthand for ``any number of
        !           126: .UL a 's,''
        !           127: so 
        !           128: .UL .*
        !           129: matches any number of anythings.
        !           130: This is used like this:
        !           131: .P1
        !           132: s/\*.*/stuff/
        !           133: .P2
        !           134: which changes an entire line,
        !           135: or
        !           136: .P1
        !           137: s/\*.*,//
        !           138: .P2
        !           139: which deletes all characters in the line up to and
        !           140: including the last comma.
        !           141: (Since
        !           142: .UL .*
        !           143: finds the longest possible match,
        !           144: this goes up to the last comma.)
        !           145: .PP
        !           146: .UL [
        !           147: is used with
        !           148: .UL ]
        !           149: to form ``character classes'';
        !           150: for example,
        !           151: .P1
        !           152: /[0123456789]/
        !           153: .P2
        !           154: matches any single digit \-
        !           155: any one of the characters inside the braces
        !           156: will cause a match.
        !           157: This can be abbreviated to
        !           158: .UL [0\-9] .
        !           159: .PP
        !           160: Finally, the
        !           161: .UL &
        !           162: is another shorthand character \-
        !           163: it is used only on the right-hand part of a substitute command
        !           164: where it means ``whatever was matched on the left-hand side''.
        !           165: It is used to save typing.
        !           166: Suppose the current line contained
        !           167: .P1
        !           168: Now is the time
        !           169: .P2
        !           170: and you wanted to put parentheses around it.
        !           171: You could just retype the line, but
        !           172: this is tedious.
        !           173: Or you could say
        !           174: .P1
        !           175: s/^/(/
        !           176: s/$/)/
        !           177: .P2
        !           178: using your knowledge of
        !           179: .UL ^
        !           180: and
        !           181: .UL $ .
        !           182: But the easiest way uses the
        !           183: .UL & :
        !           184: .P1
        !           185: s/\*.*/(&)/
        !           186: .P2
        !           187: This says ``match the whole line, and replace it
        !           188: by itself surrounded by parentheses.''
        !           189: The
        !           190: .UL &
        !           191: can be used several times in a line;
        !           192: consider
        !           193: using
        !           194: .P1
        !           195: s/\*.*/&?  &!!/
        !           196: .P2
        !           197: to produce
        !           198: .P1
        !           199: Now is the time?  Now is the time!!
        !           200: .P2
        !           201: .PP
        !           202: You don't have to match the whole line, of course:
        !           203: if the buffer contains
        !           204: .P1
        !           205: the end of the world
        !           206: .P2
        !           207: you could type
        !           208: .P1
        !           209: /world/s//& is at hand/
        !           210: .P2
        !           211: to produce
        !           212: .P1
        !           213: the end of the world is at hand
        !           214: .P2
        !           215: Observe this expression carefully,
        !           216: for it illustrates how to take advantage of
        !           217: .ul
        !           218: ed
        !           219: to save typing.
        !           220: The string
        !           221: .UL /world/
        !           222: found the desired line;
        !           223: the shorthand
        !           224: .UL //
        !           225: found the same
        !           226: word in the line;
        !           227: and the
        !           228: .UL &
        !           229: saves you from typing it again.
        !           230: .PP
        !           231: The
        !           232: .UL &
        !           233: is a special character only within
        !           234: the replacement text of a substitute command,
        !           235: and has no special meaning elsewhere.
        !           236: You can turn off the special meaning of
        !           237: .UL &
        !           238: by preceding it with a
        !           239: .UL \e :
        !           240: .P1
        !           241: s/ampersand/\e&/
        !           242: .P2
        !           243: will convert the word ``ampersand'' into the literal symbol
        !           244: .UL &
        !           245: in the current line.

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