+File: xemacs.info, Node: Regexps, Next: Search Case, Prev: Regexp Search, Up: Search
+
+Syntax of Regular Expressions
+=============================
+
+ Regular expressions have a syntax in which a few characters are
+special constructs and the rest are "ordinary". An ordinary character
+is a simple regular expression that matches that character and nothing
+else. The special characters are `.', `*', `+', `?', `[', `]', `^',
+`$', and `\'; no new special characters will be defined in the future.
+Any other character appearing in a regular expression is ordinary,
+unless a `\' precedes it.
+
+ For example, `f' is not a special character, so it is ordinary, and
+therefore `f' is a regular expression that matches the string `f' and
+no other string. (It does _not_ match the string `ff'.) Likewise, `o'
+is a regular expression that matches only `o'.
+
+ Any two regular expressions A and B can be concatenated. The result
+is a regular expression that matches a string if A matches some amount
+of the beginning of that string and B matches the rest of the string.
+
+ As a simple example, we can concatenate the regular expressions `f'
+and `o' to get the regular expression `fo', which matches only the
+string `fo'. Still trivial. To do something more powerful, you need
+to use one of the special characters. Here is a list of them:
+
+`. (Period)'
+ is a special character that matches any single character except a
+ newline. Using concatenation, we can make regular expressions
+ like `a.b', which matches any three-character string that begins
+ with `a' and ends with `b'.
+
+`*'
+ is not a construct by itself; it is a quantifying suffix operator
+ that means to repeat the preceding regular expression as many
+ times as possible. In `fo*', the `*' applies to the `o', so `fo*'
+ matches one `f' followed by any number of `o's. The case of zero
+ `o's is allowed: `fo*' does match `f'.
+
+ `*' always applies to the _smallest_ possible preceding
+ expression. Thus, `fo*' has a repeating `o', not a repeating `fo'.
+
+ The matcher processes a `*' construct by matching, immediately, as
+ many repetitions as can be found; it is "greedy". Then it
+ continues with the rest of the pattern. If that fails,
+ backtracking occurs, discarding some of the matches of the
+ `*'-modified construct in case that makes it possible to match the
+ rest of the pattern. For example, in matching `ca*ar' against the
+ string `caaar', the `a*' first tries to match all three `a's; but
+ the rest of the pattern is `ar' and there is only `r' left to
+ match, so this try fails. The next alternative is for `a*' to
+ match only two `a's. With this choice, the rest of the regexp
+ matches successfully.
+
+ Nested repetition operators can be extremely slow if they specify
+ backtracking loops. For example, it could take hours for the
+ regular expression `\(x+y*\)*a' to match the sequence
+ `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz'. The slowness is because
+ Emacs must try each imaginable way of grouping the 35 `x''s before
+ concluding that none of them can work. To make sure your regular
+ expressions run fast, check nested repetitions carefully.
+
+`+'
+ is a quantifying suffix operator similar to `*' except that the
+ preceding expression must match at least once. It is also
+ "greedy". So, for example, `ca+r' matches the strings `car' and
+ `caaaar' but not the string `cr', whereas `ca*r' matches all three
+ strings.
+
+`?'
+ is a quantifying suffix operator similar to `*', except that the
+ preceding expression can match either once or not at all. For
+ example, `ca?r' matches `car' or `cr', but does not match anything
+ else.
+
+`*?'
+ works just like `*', except that rather than matching the longest
+ match, it matches the shortest match. `*?' is known as a
+ "non-greedy" quantifier, a regexp construct borrowed from Perl.
+
+ This construct is very useful for when you want to match the text
+ inside a pair of delimiters. For instance, `/\*.*?\*/' will match
+ C comments in a string. This could not easily be achieved without
+ the use of a non-greedy quantifier.
+
+ This construct has not been available prior to XEmacs 20.4. It is
+ not available in FSF Emacs.
+
+`+?'
+ is the non-greedy version of `+'.
+
+`??'
+ is the non-greedy version of `?'.
+
+`\{n,m\}'
+ serves as an interval quantifier, analogous to `*' or `+', but
+ specifies that the expression must match at least N times, but no
+ more than M times. This syntax is supported by most Unix regexp
+ utilities, and has been introduced to XEmacs for the version 20.3.
+
+ Unfortunately, the non-greedy version of this quantifier does not
+ exist currently, although it does in Perl.
+
+`[ ... ]'
+ `[' begins a "character set", which is terminated by a `]'. In
+ the simplest case, the characters between the two brackets form
+ the set. Thus, `[ad]' matches either one `a' or one `d', and
+ `[ad]*' matches any string composed of just `a's and `d's
+ (including the empty string), from which it follows that `c[ad]*r'
+ matches `cr', `car', `cdr', `caddaar', etc.
+
+ The usual regular expression special characters are not special
+ inside a character set. A completely different set of special
+ characters exists inside character sets: `]', `-' and `^'.
+
+ `-' is used for ranges of characters. To write a range, write two
+ characters with a `-' between them. Thus, `[a-z]' matches any
+ lower case letter. Ranges may be intermixed freely with individual
+ characters, as in `[a-z$%.]', which matches any lower case letter
+ or `$', `%', or a period.
+
+ To include a `]' in a character set, make it the first character.
+ For example, `[]a]' matches `]' or `a'. To include a `-', write
+ `-' as the first character in the set, or put it immediately after
+ a range. (You can replace one individual character C with the
+ range `C-C' to make a place to put the `-'.) There is no way to
+ write a set containing just `-' and `]'.
+
+ To include `^' in a set, put it anywhere but at the beginning of
+ the set.
+
+`[^ ... ]'
+ `[^' begins a "complement character set", which matches any
+ character except the ones specified. Thus, `[^a-z0-9A-Z]' matches
+ all characters _except_ letters and digits.
+
+ `^' is not special in a character set unless it is the first
+ character. The character following the `^' is treated as if it
+ were first (thus, `-' and `]' are not special there).
+
+ Note that a complement character set can match a newline, unless
+ newline is mentioned as one of the characters not to match.
+
+`^'
+ is a special character that matches the empty string, but only at
+ the beginning of a line in the text being matched. Otherwise it
+ fails to match anything. Thus, `^foo' matches a `foo' that occurs
+ at the beginning of a line.
+
+ When matching a string instead of a buffer, `^' matches at the
+ beginning of the string or after a newline character `\n'.
+
+`$'
+ is similar to `^' but matches only at the end of a line. Thus,
+ `x+$' matches a string of one `x' or more at the end of a line.
+
+ When matching a string instead of a buffer, `$' matches at the end
+ of the string or before a newline character `\n'.
+
+`\'
+ has two functions: it quotes the special characters (including
+ `\'), and it introduces additional special constructs.
+
+ Because `\' quotes special characters, `\$' is a regular
+ expression that matches only `$', and `\[' is a regular expression
+ that matches only `[', and so on.
+
+ *Please note:* For historical compatibility, special characters are
+treated as ordinary ones if they are in contexts where their special
+meanings make no sense. For example, `*foo' treats `*' as ordinary
+since there is no preceding expression on which the `*' can act. It is
+poor practice to depend on this behavior; quote the special character
+anyway, regardless of where it appears.
+
+ For the most part, `\' followed by any character matches only that
+character. However, there are several exceptions: characters that,
+when preceded by `\', are special constructs. Such characters are
+always ordinary when encountered on their own. Here is a table of `\'
+constructs:
+
+`\|'
+ specifies an alternative. Two regular expressions A and B with
+ `\|' in between form an expression that matches anything that
+ either A or B matches.
+
+ Thus, `foo\|bar' matches either `foo' or `bar' but no other string.
+
+ `\|' applies to the largest possible surrounding expressions.
+ Only a surrounding `\( ... \)' grouping can limit the grouping
+ power of `\|'.
+
+ Full backtracking capability exists to handle multiple uses of
+ `\|'.
+
+`\( ... \)'
+ is a grouping construct that serves three purposes:
+
+ 1. To enclose a set of `\|' alternatives for other operations.
+ Thus, `\(foo\|bar\)x' matches either `foox' or `barx'.
+
+ 2. To enclose an expression for a suffix operator such as `*' to
+ act on. Thus, `ba\(na\)*' matches `bananana', etc., with any
+ (zero or more) number of `na' strings.
+
+ 3. To record a matched substring for future reference.
+
+ This last application is not a consequence of the idea of a
+ parenthetical grouping; it is a separate feature that happens to be
+ assigned as a second meaning to the same `\( ... \)' construct
+ because there is no conflict in practice between the two meanings.
+ Here is an explanation of this feature:
+
+`\DIGIT'
+ matches the same text that matched the DIGITth occurrence of a `\(
+ ... \)' construct.
+
+ In other words, after the end of a `\( ... \)' construct. the
+ matcher remembers the beginning and end of the text matched by that
+ construct. Then, later on in the regular expression, you can use
+ `\' followed by DIGIT to match that same text, whatever it may
+ have been.
+
+ The strings matching the first nine `\( ... \)' constructs
+ appearing in a regular expression are assigned numbers 1 through 9
+ in the order that the open parentheses appear in the regular
+ expression. So you can use `\1' through `\9' to refer to the text
+ matched by the corresponding `\( ... \)' constructs.
+
+ For example, `\(.*\)\1' matches any newline-free string that is
+ composed of two identical halves. The `\(.*\)' matches the first
+ half, which may be anything, but the `\1' that follows must match
+ the same exact text.
+
+`\(?: ... \)'
+ is called a "shy" grouping operator, and it is used just like `\(
+ ... \)', except that it does not cause the matched substring to be
+ recorded for future reference.
+
+ This is useful when you need a lot of grouping `\( ... \)'
+ constructs, but only want to remember one or two - or if you have
+ more than nine groupings and need to use backreferences to refer to
+ the groupings at the end.
+
+ Using `\(?: ... \)' rather than `\( ... \)' when you don't need
+ the captured substrings ought to speed up your programs some,
+ since it shortens the code path followed by the regular expression
+ engine, as well as the amount of memory allocation and string
+ copying it must do. The actual performance gain to be observed
+ has not been measured or quantified as of this writing.
+
+ The shy grouping operator has been borrowed from Perl, and has not
+ been available prior to XEmacs 20.3, nor is it available in FSF
+ Emacs.
+
+`\w'
+ matches any word-constituent character. The editor syntax table
+ determines which characters these are. *Note Syntax::.
+
+`\W'
+ matches any character that is not a word constituent.
+
+`\sCODE'
+ matches any character whose syntax is CODE. Here CODE is a
+ character that represents a syntax code: thus, `w' for word
+ constituent, `-' for whitespace, `(' for open parenthesis, etc.
+ *Note Syntax::, for a list of syntax codes and the characters that
+ stand for them.
+
+`\SCODE'
+ matches any character whose syntax is not CODE.
+
+ The following regular expression constructs match the empty
+string--that is, they don't use up any characters--but whether they
+match depends on the context.
+
+`\`'
+ matches the empty string, but only at the beginning of the buffer
+ or string being matched against.
+
+`\''
+ matches the empty string, but only at the end of the buffer or
+ string being matched against.
+
+`\='
+ matches the empty string, but only at point. (This construct is
+ not defined when matching against a string.)
+
+`\b'
+ matches the empty string, but only at the beginning or end of a
+ word. Thus, `\bfoo\b' matches any occurrence of `foo' as a
+ separate word. `\bballs?\b' matches `ball' or `balls' as a
+ separate word.
+
+`\B'
+ matches the empty string, but _not_ at the beginning or end of a
+ word.
+
+`\<'
+ matches the empty string, but only at the beginning of a word.
+
+`\>'
+ matches the empty string, but only at the end of a word.
+
+ Here is a complicated regexp used by Emacs to recognize the end of a
+sentence together with any whitespace that follows. It is given in Lisp
+syntax to enable you to distinguish the spaces from the tab characters.
+In Lisp syntax, the string constant begins and ends with a
+double-quote. `\"' stands for a double-quote as part of the regexp,
+`\\' for a backslash as part of the regexp, `\t' for a tab and `\n' for
+a newline.
+
+ "[.?!][]\"')]*\\($\\|\t\\| \\)[ \t\n]*"
+
+This regexp contains four parts: a character set matching period, `?'
+or `!'; a character set matching close-brackets, quotes or parentheses,
+repeated any number of times; an alternative in backslash-parentheses
+that matches end-of-line, a tab or two spaces; and a character set
+matching whitespace characters, repeated any number of times.
+
+\1f
+File: xemacs.info, Node: Search Case, Next: Replace, Prev: Regexps, Up: Search
+
+Searching and Case
+==================
+
+ All searches in Emacs normally ignore the case of the text they are
+searching through; if you specify searching for `FOO', `Foo' and `foo'
+are also considered a match. Regexps, and in particular character
+sets, are included: `[aB]' matches `a' or `A' or `b' or `B'.
+
+ If you want a case-sensitive search, set the variable
+`case-fold-search' to `nil'. Then all letters must match exactly,
+including case. `case-fold-search' is a per-buffer variable; altering
+it affects only the current buffer, but there is a default value which
+you can change as well. *Note Locals::. You can also use Case
+Sensitive Search from the Options menu on your screen.
+
+\1f
+File: xemacs.info, Node: Replace, Next: Other Repeating Search, Prev: Search Case, Up: Search
+
+Replacement Commands
+====================
+
+ Global search-and-replace operations are not needed as often in
+Emacs as they are in other editors, but they are available. In
+addition to the simple `replace-string' command which is like that
+found in most editors, there is a `query-replace' command which asks
+you, for each occurrence of a pattern, whether to replace it.
+
+ The replace commands all replace one string (or regexp) with one
+replacement string. It is possible to perform several replacements in
+parallel using the command `expand-region-abbrevs'. *Note Expanding
+Abbrevs::.
+
+* Menu:
+
+* Unconditional Replace:: Replacing all matches for a string.
+* Regexp Replace:: Replacing all matches for a regexp.
+* Replacement and Case:: How replacements preserve case of letters.
+* Query Replace:: How to use querying.
+
+\1f
+File: xemacs.info, Node: Unconditional Replace, Next: Regexp Replace, Prev: Replace, Up: Replace
+
+Unconditional Replacement
+-------------------------
+
+`M-x replace-string <RET> STRING <RET> NEWSTRING <RET>'
+ Replace every occurrence of STRING with NEWSTRING.
+
+`M-x replace-regexp <RET> REGEXP <RET> NEWSTRING <RET>'
+ Replace every match for REGEXP with NEWSTRING.
+
+ To replace every instance of `foo' after point with `bar', use the
+command `M-x replace-string' with the two arguments `foo' and `bar'.
+Replacement occurs only after point: if you want to cover the whole
+buffer you must go to the beginning first. By default, all occurrences
+up to the end of the buffer are replaced. To limit replacement to part
+of the buffer, narrow to that part of the buffer before doing the
+replacement (*note Narrowing::).
+
+ When `replace-string' exits, point is left at the last occurrence
+replaced. The value of point when the `replace-string' command was
+issued is remembered on the mark ring; `C-u C-<SPC>' moves back there.
+
+ A numeric argument restricts replacement to matches that are
+surrounded by word boundaries.
+
+\1f
+File: xemacs.info, Node: Regexp Replace, Next: Replacement and Case, Prev: Unconditional Replace, Up: Replace
+
+Regexp Replacement
+------------------
+
+ `replace-string' replaces exact matches for a single string. The
+similar command `replace-regexp' replaces any match for a specified
+pattern.
+
+ In `replace-regexp', the NEWSTRING need not be constant. It can
+refer to all or part of what is matched by the REGEXP. `\&' in
+NEWSTRING stands for the entire text being replaced. `\D' in
+NEWSTRING, where D is a digit, stands for whatever matched the D'th
+parenthesized grouping in REGEXP. For example,
+
+ M-x replace-regexp <RET> c[ad]+r <RET> \&-safe <RET>
+
+would replace (for example) `cadr' with `cadr-safe' and `cddr' with
+`cddr-safe'.
+
+ M-x replace-regexp <RET> \(c[ad]+r\)-safe <RET> \1 <RET>
+
+would perform exactly the opposite replacements. To include a `\' in
+the text to replace with, you must give `\\'.
+
+\1f
+File: xemacs.info, Node: Replacement and Case, Next: Query Replace, Prev: Regexp Replace, Up: Replace
+
+Replace Commands and Case
+-------------------------
+
+ If the arguments to a replace command are in lower case, the command
+preserves case when it makes a replacement. Thus, the following
+command:
+
+ M-x replace-string <RET> foo <RET> bar <RET>
+
+replaces a lower-case `foo' with a lower case `bar', `FOO' with `BAR',
+and `Foo' with `Bar'. If upper-case letters are used in the second
+argument, they remain upper-case every time that argument is inserted.
+If upper-case letters are used in the first argument, the second
+argument is always substituted exactly as given, with no case
+conversion. Likewise, if the variable `case-replace' is set to `nil',
+replacement is done without case conversion. If `case-fold-search' is
+set to `nil', case is significant in matching occurrences of `foo' to
+replace; also, case conversion of the replacement string is not done.
+
+\1f
+File: xemacs.info, Node: Query Replace, Prev: Replacement and Case, Up: Replace
+
+Query Replace
+-------------
+
+`M-% STRING <RET> NEWSTRING <RET>'
+`M-x query-replace <RET> STRING <RET> NEWSTRING <RET>'
+ Replace some occurrences of STRING with NEWSTRING.
+
+`M-x query-replace-regexp <RET> REGEXP <RET> NEWSTRING <RET>'
+ Replace some matches for REGEXP with NEWSTRING.
+
+ If you want to change only some of the occurrences of `foo' to
+`bar', not all of them, you can use `query-replace' instead of `M-%'.
+This command finds occurrences of `foo' one by one, displays each
+occurrence, and asks you whether to replace it. A numeric argument to
+`query-replace' tells it to consider only occurrences that are bounded
+by word-delimiter characters.
+
+ Aside from querying, `query-replace' works just like
+`replace-string', and `query-replace-regexp' works just like
+`replace-regexp'.
+
+ The things you can type when you are shown an occurrence of STRING
+or a match for REGEXP are:
+
+`<SPC>'
+ to replace the occurrence with NEWSTRING. This preserves case,
+ just like `replace-string', provided `case-replace' is non-`nil',
+ as it normally is.
+
+`<DEL>'
+ to skip to the next occurrence without replacing this one.
+
+`, (Comma)'
+ to replace this occurrence and display the result. You are then
+ prompted for another input character. However, since the
+ replacement has already been made, <DEL> and <SPC> are equivalent.
+ At this point, you can type `C-r' (see below) to alter the
+ replaced text. To undo the replacement, you can type `C-x u'.
+ This exits the `query-replace'. If you want to do further
+ replacement you must use `C-x ESC' to restart (*note Repetition::).
+
+`<ESC>'
+ to exit without doing any more replacements.
+
+`. (Period)'
+ to replace this occurrence and then exit.
+
+`!'
+ to replace all remaining occurrences without asking again.
+
+`^'
+ to go back to the location of the previous occurrence (or what
+ used to be an occurrence), in case you changed it by mistake.
+ This works by popping the mark ring. Only one `^' in a row is
+ allowed, because only one previous replacement location is kept
+ during `query-replace'.
+
+`C-r'
+ to enter a recursive editing level, in case the occurrence needs
+ to be edited rather than just replaced with NEWSTRING. When you
+ are done, exit the recursive editing level with `C-M-c' and the
+ next occurrence will be displayed. *Note Recursive Edit::.
+
+`C-w'
+ to delete the occurrence, and then enter a recursive editing level
+ as in `C-r'. Use the recursive edit to insert text to replace the
+ deleted occurrence of STRING. When done, exit the recursive
+ editing level with `C-M-c' and the next occurrence will be
+ displayed.
+
+`C-l'
+ to redisplay the screen and then give another answer.
+
+`C-h'
+ to display a message summarizing these options, then give another
+ answer.
+
+ If you type any other character, Emacs exits the `query-replace', and
+executes the character as a command. To restart the `query-replace',
+use `C-x <ESC>', which repeats the `query-replace' because it used the
+minibuffer to read its arguments. *Note C-x ESC: Repetition.
+
+\1f
+File: xemacs.info, Node: Other Repeating Search, Prev: Replace, Up: Search
+
+Other Search-and-Loop Commands
+==============================
+
+ Here are some other commands that find matches for a regular
+expression. They all operate from point to the end of the buffer.
+
+`M-x occur'
+ Print each line that follows point and contains a match for the
+ specified regexp. A numeric argument specifies the number of
+ context lines to print before and after each matching line; the
+ default is none.
+
+ The buffer `*Occur*' containing the output serves as a menu for
+ finding occurrences in their original context. Find an occurrence
+ as listed in `*Occur*', position point there, and type `C-c C-c';
+ this switches to the buffer that was searched and moves point to
+ the original of the same occurrence.
+
+`M-x list-matching-lines'
+ Synonym for `M-x occur'.
+
+`M-x count-matches'
+ Print the number of matches following point for the specified
+ regexp.
+
+`M-x delete-non-matching-lines'
+ Delete each line that follows point and does not contain a match
+ for the specified regexp.
+
+`M-x delete-matching-lines'
+ Delete each line that follows point and contains a match for the
+ specified regexp.
+
+\1f
+File: xemacs.info, Node: Fixit, Next: Files, Prev: Search, Up: Top
+
+Commands for Fixing Typos
+*************************
+
+ This chapter describes commands that are especially useful when you
+catch a mistake in your text just after you have made it, or when you
+change your mind while composing text on line.
+
+* Menu:
+
+* Kill Errors:: Commands to kill a batch of recently entered text.
+* Transpose:: Exchanging two characters, words, lines, lists...
+* Fixing Case:: Correcting case of last word entered.
+* Spelling:: Apply spelling checker to a word, or a whole file.
+
+\1f
+File: xemacs.info, Node: Kill Errors, Next: Transpose, Prev: Fixit, Up: Fixit
+
+Killing Your Mistakes
+=====================
+
+`<DEL>'
+ Delete last character (`delete-backward-char').
+
+`M-<DEL>'
+ Kill last word (`backward-kill-word').
+
+`C-x <DEL>'
+ Kill to beginning of sentence (`backward-kill-sentence').
+
+ The <DEL> character (`delete-backward-char') is the most important
+correction command. When used among graphic (self-inserting)
+characters, it can be thought of as canceling the last character typed.
+
+ When your mistake is longer than a couple of characters, it might be
+more convenient to use `M-<DEL>' or `C-x <DEL>'. `M-<DEL>' kills back
+to the start of the last word, and `C-x <DEL>' kills back to the start
+of the last sentence. `C-x <DEL>' is particularly useful when you are
+thinking of what to write as you type it, in case you change your mind
+about phrasing. `M-<DEL>' and `C-x <DEL>' save the killed text for
+`C-y' and `M-y' to retrieve. *Note Yanking::.
+
+ `M-<DEL>' is often useful even when you have typed only a few
+characters wrong, if you know you are confused in your typing and aren't
+sure exactly what you typed. At such a time, you cannot correct with
+<DEL> except by looking at the screen to see what you did. It requires
+less thought to kill the whole word and start over.
+
+\1f
projects / chise / xemacs-chise.git / blobdiff