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     Elvis 1.4               REGULAR EXPRESSIONS                Page 4-1


E4.  REGULAR EXPRESSIONSF

        Elvis uses regular expressions for searching and substututions.  


   E4.1  SyntaxF

        Elvis' regexp package treats the following one- or two-character 
     strings (called meta-characters) in special ways: 

                \( \)   Used to delimit subexpressions
                ^       Matches the beginning of a line
                $       Matches the end of a line
                \<      Matches the beginning of a word
                \>      Matches the end of a word
                [ ]     Matches any single character inside the brackets
                *       The preceding may be repeated 0 or more times
                \+      The preceding may be repeated 1 or more times
                \?      The preceding is optional

        Anything  else is treated as a normal character which must match
     exactly.  The special strings may all be preceded by a backslash to 
     force them to be treated normally.  


   E4.2  OptionsF

        Elvis has two options which affect the way  regular  expressions
     are used.    These  options  may  be  examined  or set via the :set
     command.  

        The first option is called  "[no]magic".    This  is  a  boolean
     option, and  it is "magic" (TRUE) by default.  While in magic mode,
     all of the meta-characters behave as described above.   In  nomagic
     mode, only ^ and $ retain their special meaning.  

        The second option is called "[no]ignorecase".  This is a boolean 
     option, and  it  is  "noignorecase"  (FALSE)  by default.  While in
     ignorecase mode,  the  searching  mechanism  will  not  distinguish
     between an   uppercase   letter   and   its  lowercase  form.    In
     noignorecase mode, uppercase and lowercase  are  treated  as  being
     different.  

        Also, the "[no]wrapscan" option affects searches.  


   E4.3  SubstitutionsF

        The :s command has at least two arguments: a regular expression, 
     and a  substitution  string.    The  text  that matched the regular
     expression  is  replaced  by  text  which  is  derived   from   the
     substitution string.  











     Elvis 1.4               REGULAR EXPRESSIONS                Page 4-2


        Most  characters  in the substitution string are copied into the
     text literally but a few have special meaning: 

        &       Insert a copy of the original text
        ~       Insert a copy of the previous replacement text
        \1      Insert a copy of that portion of the original text which
                matched the first set of \( \) parentheses.
        \2 - \9 Does the same for the second (etc.) pair of \( \).
        \U      Convert all chars of any later &, ~, or \# to uppercase
        \L      Convert all chars of any later &, ~, or \# to lowercase
        \E      End the effect of \U or \L
        \u      Convert the first char of the next &, ~ or \# to uppercase
        \l      Convert the first char of the next &, ~ or \# to lowercase

        These may be preceded by a backslash to force them to be treated 
     normally.  If "nomagic" mode is in effect, then &  and  ~  will  be
     treated normally, and you must write them as \& and \~ form them to 
     have special meaning.  


   E4.4  ExamplesF

        This example changes every occurence of "utilize" to "use": 

            :%s/utilize/use/g

        This  example deletes all whitespace that occurs at the end of a
     line anywhere in the file.  (The brackets contain  a  single  space
     and a single tab.): 

            :%s/[   ]\+$//

        This example converts the current line to uppercase: 

            :s/.*/\U&/

        This  example  underlines  each  letter  in the current line, by
     changing it into an "underscore backspace letter" sequence.    (The
     ^H is entered as "control-V backspace".): 

            :s/[a-zA-Z]/_^H&/g

        This  example  locates  the  last colon in a line, and swaps the
     text before the colon with the text after the colon.  The first  \(
     \)  pair  is  used to delineate the stuff before the colon, and the
     second pair delineates the stuff after.  In the substitution  text,
     \1 and \2 are given in reverse order, to perform the swap: 

            :s/\(.*\):\(.*\)/\2:\1/
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