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This is Info file elisp, produced by Makeinfo-1.47 from the input file elisp.texi. This file documents GNU Emacs Lisp. This is edition 1.03 of the GNU Emacs Lisp Reference Manual, for Emacs Version 18. Published by the Free Software Foundation, 675 Massachusetts Avenue, Cambridge, MA 02139 USA Copyright (C) 1990 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. File: elisp, Node: Case Changes, Next: Substitution, Prev: Columns, Up: Text Case Changes ============ The case change commands described here work on text in the current buffer. *Note Character Case::, for case conversion commands that work on strings and characters. -- Command: capitalize-region START END This function capitalizes all words in the region defined by START and END. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. The function returns `nil'. If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word. When `capitalize-region' is called interactively, START and END are point and the mark, with the smallest first. ---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ---------- -- Command: downcase-region START END This function converts all of the letters in the region defined by START and END to lower case. The function returns `nil'. When `downcase-region' is called interactively, START and END are point and the mark, with the smallest first. -- Command: upcase-region START END This function converts all of the letters in the region defined by START and END to upper case. The function returns `nil'. When `upcase-region' is called interactively, START and END are point and the mark, with the smallest first. -- Command: capitalize-word COUNT This function capitalizes COUNT words after point, moving point over as it does. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. If COUNT is negative, the function capitalizes the -COUNT previous words but does not move point. The value is `nil'. If point is in the middle of a word, the part of word the before point (if moving forward) or after point (if operating backward) is ignored. The rest is treated as an entire word. When `capitalize-word' is called interactively, COUNT is set to the numeric prefix argument. -- Command: downcase-word COUNT This function converts the COUNT words after point to all lower case, moving point over as it does. If COUNT is negative, it converts the -COUNT previous words but does not move point. The value is `nil'. When `downcase-word' is called interactively, COUNT is set to the numeric prefix argument. -- Command: upcase-word COUNT This function converts the COUNT words after point to all upper case, moving point over as it does. If COUNT is negative, it converts the -COUNT previous words but does not move point. The value is `nil'. When `upcase-word' is called interactively, COUNT is set to the numeric prefix argument. File: elisp, Node: Substitution, Next: Underlining, Prev: Case Changes, Up: Text Substituting for a Character Code ================================= The following function replaces characters within a specified region based on their character code. -- Function: subst-char-in-region START END OLD-CHAR NEW-CHAR &optional NOUNDO This function replaces all occurrences of the character OLD-CHAR with the character NEW-CHAR in the region of the current buffer defined by START and END. If NOUNDO is non-`nil', then `subst-char-in-region' does not record the change for undo and does not mark the buffer as modified. This feature is useful for changes which are not considered significant, such as when Outline mode changes visible lines to invisible lines and vice versa. `subst-char-in-region' does not move point and returns `nil'. ---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) => nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ---------- File: elisp, Node: Underlining, Next: Registers, Prev: Substitution, Up: Text Underlining =========== The underlining commands are somewhat obsolete. The `underline-region' function actually inserts `_^H' before each appropriate character in the region. This command provides a minimal text formatting feature that might work on your printer; however, we recommend instead that you use more powerful text formatting facilities, such as Texinfo. -- Command: underline-region START END This function underlines all nonblank characters in the region defined by START and END. That is, an underscore character and a backspace character are inserted just before each non-whitespace character in the region. The backspace characters are intended to cause overstriking, but in Emacs they display as either `\010' or `^H', depending on the setting of `ctl-arrow'. There is no way to see the effect of the overstriking within Emacs. The value is `nil'. -- Command: ununderline-region START END This function removes all underlining (overstruck underscores) in the region defined by START and END. The value is `nil'. File: elisp, Node: Registers, Prev: Underlining, Up: Text Registers ========= A register is a sort of variable used in Emacs editing that can hold a marker, a string, or a rectangle. Each register is named by a single character. All characters, including control and meta characters (but with the exception of `C-g'), can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by a character which is its name. The functions in this section return unpredictable values unless otherwise stated. -- Variable: register-alist This variable is an alist of elements of the form `(NAME . CONTENTS)'. Normally, there is one element for each Emacs register that has been used. The object NAME is a character (an integer) identifying the register. The object CONTENTS is a string, marker, or list representing the register contents. A string represents text stored in the register. A marker represents a position. A list represents a rectangle; its elements are strings, one per line of the rectangle. -- Command: view-register REG This command displays what is contained in register REG. -- Function: get-register REG This function returns the contents of the register REG, or `nil' if it has no contents. -- Function: set-register REG VALUE This function sets the contents of register REG to VALUE. A register can be set to any value, but the other register functions expect only strings, markers, and lists. -- Command: point-to-register REG This command stores both the current location of point and the current buffer in register REG as a marker. -- Command: register-to-point REG This command moves point to the position stored in register REG. Since both the buffer and the location within the buffer are stored by the `point-to-register' function, this command can switch you to another buffer. If the register does not contain a saved position (a marker), then an error is signaled. -- Command: insert-register REG &optional BEFOREP This command inserts contents of register REG into the current buffer. Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument BEFOREP is non-`nil', it puts the mark before and point after. You can pass a non-`nil' second argument BEFOREP to this function interactively by supplying any prefix argument. If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines. If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future. -- Command: copy-to-register REG START END &optional DELETE-FLAG This command copies the region from START to END into register REG. If DELETE-FLAG is non-`nil', it deletes the region from the buffer after copying it into the register. -- Command: prepend-to-register REG START END &optional DELETE-FLAG This command prepends the region from START to END into register REG. If DELETE-FLAG is non-`nil', it deletes the region from the buffer after copying it to the register. -- Command: append-to-register REG START END &optional DELETE-FLAG This command appends the region from START to END to the text already in register REG. If DELETE-FLAG is non-`nil', it deletes the region from the buffer after copying it to the register. -- Command: copy-rectangle-to-register REG START END &optional DELETE-FLAG This command copies a rectangular region from START to END into register REG. If DELETE-FLAG is non-`nil', it deletes the region from the buffer after copying it to the register. File: elisp, Node: Searching and Matching, Next: Syntax Tables, Prev: Text, Up: Top Searching and Matching ********************** GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can identify the text matched by parts of the regular expression by examining the "match data". * Menu: * String Search:: Search for an exact match. * Regular Expressions:: Describing classes of strings. * Regexp Search:: Searching for a match for a regexp. * Match Data:: Finding out which part of the text matched various parts of a regexp, after regexp search. * Saving Match Data:: Saving and restoring this information. * Standard Regexps:: Useful regexps for finding sentences, pages,... * Searching and Case:: Case-independent or case-significant searching. File: elisp, Node: String Search, Next: Regular Expressions, Prev: Searching and Matching, Up: Searching and Matching Searching for Strings ===================== These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; LIMIT and NOERROR are set to `nil', and REPEAT is set to 1. -- Command: search-forward STRING &optional LIMIT NOERROR REPEAT This function searches forward from point for an exact match for STRING. It sets point to the end of the occurrence found, and returns `t'. If no match is found, the value and side effects depend on NOERROR. In the following example, point is positioned at the beginning of the line. Then `(search-forward "fox")' is evaluated in the minibuffer and point is left after the last letter of `fox': ---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => t ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ---------- If LIMIT is non-`nil', then it is the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. What happens when the search fails depends on the value of NOERROR. If NOERROR is `nil', a `search-failed' error is signaled. If NOERROR is `t', `search-forward' returns `nil' and doesn't signal an error. If NOERROR is neither `nil' nor `t', then `search-forward' moves point to LIMIT and returns `nil'. If REPEAT is non-`nil', then the search is repeated that many times. Point is positioned at the end of the last match. -- Command: search-backward STRING &optional LIMIT NOERROR REPEAT This function searches backward from point for STRING. It is just like `search-forward' except that it searches backwards and leaves point at the beginning of the match. -- Command: word-search-forward STRING &optional LIMIT NOERROR REPEAT This function searches forward from point for a "word" match for STRING. It sets point to the end of the occurrence found, and returns `t'. A word search differs from a simple string search in that a word search *requires* that the words it searches for are present as entire words (searching for the word `ball' will not match the word `balls'), and punctuation and spacing are ignored (searching for `ball boy' will match `ball. Boy!'). In this example, point is first placed at the beginning of the buffer; the search leaves it between the `y' and the `!'. ---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => t ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ---------- If LIMIT is non-`nil' (it must be a position in the current buffer), then it is the upper bound to the search. The match found must not extend after that position. If NOERROR is `t', then `word-search-forward' returns `nil' when a search fails, instead of signaling an error. If NOERROR is neither `nil' nor `t', then `word-search-forward' moves point to LIMIT and returns `nil'. If REPEAT is non-`nil', then the search is repeated that many times. Point is positioned at the end of the last match. -- Command: word-search-backward STRING &optional LIMIT NOERROR REPEAT This function searches backward from point for a word match to STRING. This function is just like `word-search-forward' except that it searches backward and normally leaves point at the beginning of the match. File: elisp, Node: Regular Expressions, Next: Regexp Search, Prev: String Search, Up: Searching and Matching Regular Expressions =================== A "regular expression" ("regexp", for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them. * Menu: * Syntax of Regexps:: Rules for writing regular expressions. * Regexp Example:: Illustrates regular expression syntax. File: elisp, Node: Syntax of Regexps, Next: Regexp Example, Prev: Regular Expressions, Up: Regular Expressions 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 which 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 which 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 which begins with `a' and ends with `b'. `*' is not a construct by itself; it is a suffix that means the preceding regular expression is to be repeated 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. 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, 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. `+' is a suffix character similar to `*' except that it must match the preceding expression at least once. So, for example, `ca+r' will match the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' would match all three strings. `?' is a suffix character similar to `*' except that it can match the preceding expression either once or not at all. For example, `ca?r' will match `car' or `cr'; nothing else. `[ ... ]' `[' begins a "character set", which is terminated by a `]'. In the simplest case, the characters between the two 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. Character ranges can also be included in a character set, by writing 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 `$', `%' or a period. Note that the usual special characters are not special any more inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'. To include a `]' in a character set, make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `---', which is a range containing only `-', or write `-' as the first character in the range. To include `^', make it other than the first character in the set. `[^ ... ]' `[^' begins a "complement character set", which matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters *except* letters and digits. `^' is not special in a character set unless it is the first character. The character following the `^' is treated as if it were first (thus, `-' and `]' are not special there). Note that a complement character set can match a newline, unless newline is mentioned as one of the characters not to match. `^' is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, `^foo' matches a `foo' which occurs at the beginning of a line. When matching a string, `^' matches at the beginning of the string or after a newline character `\n'. `$' is similar to `^' but matches only at the end of a line. Thus, `x+$' matches a string of one `x' or more at the end of a line. When matching a string, `$' 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 which matches only `$', and `\[' is a regular expression which matches only `[', and so on. Note that `\' also has special meaning in the read syntax of Lisp strings (*note String Type::.), and must be quoted with `\'. For example, the regular expression that matches the `\' character is `\\'. To write a Lisp string that contains `\\', Lisp syntax requires you to quote each `\' with another `\'. Therefore, the read syntax for this string is `"\\\\"'. *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; better to 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 which, 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$x' matches either `foox' or `barx'. 2. To enclose a complicated expression for a suffix character such as `*' to operate on. Thus, `ba$na$*' matches `bananana', etc., with any (zero or more) number of `na' strings. 3. To record a matched substring for future reference. This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature which happens to be assigned as a second meaning to the same `$ ... $' construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature: `\DIGIT' after the end of a `$ ... $' construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use `\' followed by DIGIT to mean "match the same text matched the DIGITth time by the `$ ... $' construct." The strings matching the first nine `$ ... $' constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. `\1' through `\9' can be used to refer to the text matched by the corresponding `$ ... $' construct. For example, `$.*$\1' matches any newline-free string that is composed of two identical halves. The `$.*$' matches the first half, which may be anything, but the `\1' that follows must match the same exact text. `\`' matches the empty string, provided it is at the beginning of the buffer. `\'' matches the empty string, provided it is at the end of the buffer. `\b' matches the empty string, provided it is at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word. `\B' matches the empty string, provided it is *not* at the beginning or end of a word. `\<' matches the empty string, provided it is at the beginning of a word. `\>' matches the empty string, provided it is at the end of a word. `\w' matches any word-constituent character. The editor syntax table determines which characters these are. *Note Syntax Tables::. `\W' matches any character that is not a word-constituent. `\sCODE' matches any character whose syntax is CODE. Here CODE is a character which represents a syntax code: thus, `w' for word constituent, `-' for whitespace, `(' for open parenthesis, etc. *Note Syntax Tables::, for a list of the codes. `\SCODE' matches any character whose syntax is not CODE. Not every string is a valid regular expression. For example, any string with unbalanced square brackets is invalid, and so is a string that ends with a single `\'. If an invalid regular expression is passed to any of the search functions, an `invalid-regexp' error is signaled. -- Function: regexp-quote STRING This function returns a regular expression string which matches exactly STRING and nothing else. This allows you to request an exact string match when calling a function that wants a regular expression. (regexp-quote "^The cat$") => "\\^The cat\\$" One use of `regexp-quote' is to combine an exact string match with context described as a regular expression. For example, this searches for the string which is the value of `string', surrounded by whitespace: (re-search-forward (concat "\\s " (regexp-quote string) "\\s ")) File: elisp, Node: Regexp Example, Prev: Syntax of Regexps, Up: Regular Expressions Complex Regexp Example ---------------------- Here is a complicated regexp, used by Emacs to recognize the end of a sentence together with any whitespace that follows. It is the value of the variable `sentence-end'. First, we show the regexp as a string in Lisp syntax to enable you to distinguish the spaces from the tab characters. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline. "[.?!][]\"')}]*\$$\\|\t\\| \$[ \t\n]*" In contrast, if you evaluate the variable `sentence-end', you will see the following: sentence-end => "[.?!][]\"')}]*\$$\\| \\| \$[ ]*" In this case, the tab and carriage return are the actual characters. This regular expression contains four parts in succession and can be deciphered as follows: `[.?!]' The first part of the pattern consists of three characters, a period, a question mark and an exclamation mark, within square brackets. The match must begin with one of these three characters. `[]\"')}]*' The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The `\"' is Lisp syntax for a double-quote in a string. The `*' at the end indicates that the immediately preceding regular expression (a character set, in this case) may be repeated zero or more times. `\$$\\|\t\\| \$' The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line, or a tab, or two spaces. The double backslashes are needed to prevent Emacs from reading the parentheses and vertical bars as part of the search pattern; the parentheses are used to mark the group and the vertical bars are used to indicated that the patterns to either side of them are alternatives. The dollar sign is used to match the end of a line. The tab character is written using `\t' and the two spaces are written as themselves. `[ \t\n]*' Finally, the last part of the pattern indicates that the end of the line or the whitespace following the period, question mark or exclamation mark may, but need not, be followed by additional whitespace. File: elisp, Node: Regexp Search, Next: Match Data, Prev: Regular Expressions, Up: Searching and Matching Regular Expression Searching ============================ In GNU Emacs, you can search for the next match for a regexp either incrementally or not. Incremental search commands are described in the `The GNU Emacs Manual'. *Note Regular Expression Search: (emacs)Regexp Search. Here we describe only the search functions useful in programs. The principal is `re-search-forward'. -- Command: re-search-forward REGEXP &optional LIMIT NOERROR REPEAT This function searches forward in the current buffer for a string of text that is matched by the regular expression REGEXP. The function skips over any amount of text that is not matched by REGEXP, and leaves point at the end of the first string found that does match. If the search is successful (i.e., if text matching REGEXP is found), then point is left at the end of that text, and the function returns `t'. What happens when the search fails depends on the value of NOERROR. If NOERROR is `nil', a `search-failed' error is signaled. If NOERROR is `t', `re-search-forward' returns `nil' and doesn't signal an error. If NOERROR is neither `nil' nor `t', then `search-forward' moves point to LIMIT and returns `nil'. If LIMIT is non-`nil' (it must be a position in the current buffer), then it is the upper bound to the search. No match extending after that position is accepted. If REPEAT is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). The call succeeds if all these searches succeeded, and point is left at the end of the match found by the last search. Otherwise the search fails. In the following example, point is initially located directly before the `T'. After evaluating the form, point is located at the end of that line (between the `t' of `hat' and before the newline). ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => t ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- -- Command: re-search-backward REGEXP &optional LIMIT NOERROR REPEAT This function searches backward in the current buffer for a string of text that is matched by the regular expression REGEXP, leaving point at the beginning of the first text found. This function is analogous to `re-search-forward', but they are not simple mirror images. `re-search-forward' finds the match whose beginning is as close as possible. If `re-search-backward' were a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible. The reason is that matching a regular expression at a given spot always works from beginning to end, and is done at a specified beginning position. Thus, true mirror-image behavior would require a special feature for matching regexps from end to beginning. -- Function: string-match REGEXP STRING &optional START This function returns the index of the start of the first match for the regular expression REGEXP in STRING, or `nil' if there is no match. If START is non-`nil', the search starts at that index in STRING. For example, (string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 The index of the first character of the string is 0, the index of the second character is 1, and so on. After this function returns, the index of the first character beyond the match is available as `(match-end 0)'. *Note Match Data::. (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32 The `match-end' function is described along with `match-beginning'; see *Note Match Data::. -- Function: looking-at REGEXP This function determines whether the text in the current buffer directly following point matches the regular expression REGEXP. "Directly following" means precisely that: the search is "anchored" and it must succeed starting with the first character following point. The result is `t' if so, `nil' otherwise. Point is not moved, but the match data is updated and can be used with `match-beginning' or `match-end'. *Note Match Data::. In this example, point is located directly before the `T'. If it were anywhere else, the result would be `nil'. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t File: elisp, Node: Match Data, Next: Saving Match Data, Prev: Regexp Search, Up: Searching and Matching The Match Data ============== Emacs keeps track of the positions of the start and end of segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and extract parts of it. -- Function: match-beginning COUNT This function returns the position of the start of text matched by the last regular expression searched for. COUNT, a number, specifies a subexpression whose start position is the value. If COUNT is zero, then the value is the position of the text matched by the whole regexp. If COUNT is greater than zero, then the value is the position of the beginning of the text matched by the COUNTth subexpression, regardless of whether it was used in the final match. Subexpressions of a regular expression are those expressions grouped inside of parentheses, `$...$'. The COUNTth subexpression is found by counting occurrences of `$' from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. The `match-end' function is similar to the `match-beginning' function except that it returns the position of the end of the matched text. Here is an example, with a comment showing the numbers of the positions in the text: (string-match "\\(qu\$\$ick\$" "The quick fox jumped quickly.") => 4 ;^^^^^^^^^^ ;0123456789 (match-beginning 1) ; The beginning of the match => 4 ; with `qu' is at index 4. (match-beginning 2) ; The beginning of the match => 6 ; with `ick' is at index 6. (match-end 1) ; The end of the match => 6 ; with `qu' is at index 6. (match-end 2) ; The end of the match => 9 ; with `ick' is at index 9. Here is another example. Before the form is evaluated, point is located at the beginning of the line. After evaluating the search form, point is located on the line between the space and the word `in'. The beginning of the entire match is at the 9th character of the buffer (`T'), and the beginning of the match for the first subexpression is at the 13th character (`c'). (list (re-search-forward "The \$cat \$") (match-beginning 0) (match-beginning 1)) => (t 9 13) ---------- Buffer: foo ---------- I read "The cat -!-in the hat comes back" twice. ^ ^ 9 13 ---------- Buffer: foo ---------- (Note that in this case, the index returned is a buffer position; the first character of the buffer counts as 1.) It is essential that `match-beginning' be called after the search desired, but before any other searches are performed. `match-beginning' may not give the desired results if any other Lisp programs are executed between the search and it, since they may do other searches. This example shows misuse of `match-beginning'. (re-search-forward "The \$cat \$") => t (foo) ; Perhaps `foo' does more regexp searching. (match-beginning 0) => 61 ; Unexpected result! See the discussion of `store-match-data' for an example of how to save and restore the match data around a search. -- Function: match-end COUNT This function returns the position of the end of text matched by the last regular expression searched for. This function is otherwise similar to `match-beginning'. -- Function: replace-match REPLACEMENT &optional FIXEDCASE LITERAL This function replaces the text matched by the last search with REPLACEMENT. If FIXEDCASE is non-`nil', then the case of the replacement text is not changed; otherwise, the replacement text is converted to a different case depending upon the capitalization of the text to be replaced. If the original text is all upper case, the replacement text is converted to upper case, except when all of the words in the original text are only one character long. In that event, the replacement text is capitalized. If *all* of the words in the original text are capitalized, then all of the words in the replacement text are capitalized. If LITERAL is non-`nil', then REPLACEMENT is inserted exactly as it is, the only alterations being case changes as needed. If it is `nil' (the default), then the character `\' is treated specially. If a `\' appears in REPLACEMENT, then it must be part of one of the following sequences: `\&' `\&' stands for the entire text being replaced. `\N' `\N' stands for the Nth subexpression in the original regexp. Subexpressions are those expressions grouped inside of `$...$'. N is a digit. `\\' `\\' stands for a single `\' in the replacement text. `replace-match' leaves point at the end of the replacement text, and returns `t'. File: elisp, Node: Saving Match Data, Next: Standard Regexps, Prev: Match Data, Up: Searching and Matching Saving and Restoring the Match Data =================================== -- Function: match-data This function returns a new list containing all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression. In general, element number 2N corresponds to `(match-beginning N)'; and element number 2N + 1 corresponds to `(match-end N)'. All the elements are markers, or the integer 0 for a match at the beginning of a string (with `string-match'), or `nil' if there was no match for that subexpression. As with other functions that get information about a search, there must be no possibility of intervening searches between the call to a search function and the call to `match-data' that is intended to save the match-data for that search. (match-data) => (#<marker at 9 in foo> #<marker at 17 in foo> #<marker at 13 in foo> #<marker at 17 in foo>) In version 19, all elements will be markers or `nil' if matching was done on a buffer, and all will be integers or `nil' if matching was done on a string with `string-match'. -- Function: store-match-data MATCH-LIST This function sets the match data within Emacs Lisp from the elements of MATCH-LIST, which should be a list created by a previous call to `match-data'. `store-match-data' may be used together with `match-data' to perform a search without changing the `match-data'. This is useful when such searches occur in subroutines whose callers may not expect searches to go on. Here is how: (let ((data (match-data))) (unwind-protect ... ; May change the original match data. (store-match-data data))) All asynchronous process functions (filters and sentinels) and some modes that use `recursive-edit' should save and restore the match data if they do a search or if they let the user type arbitrary commands. Here is a function which will restore the match data if the buffer associated with it still exists. (defun restore-match-data (data) "Restore the match data DATA unless the buffer is missing." (catch 'foo (let ((d data)) (while d (and (car d) (null (marker-buffer (car d))) ;; match-data buffer is deleted. (throw 'foo nil)) (setq d (cdr d))) (store-match-data data)))) File: elisp, Node: Standard Regexps, Next: Searching and Case, Prev: Saving Match Data, Up: Searching and Matching Standard Regular Expressions Used in Editing ============================================ -- Variable: page-delimiter This is the regexp describing line-beginnings that separate pages. The default value is `"^\014"' (i.e., `"^^L"' or `"^\C-l"'). -- Variable: paragraph-separate This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change `paragraph-start' also.) The default value is `"^[ \t\f]*$"', which is a line that consists entirely of spaces, tabs, and form feeds. -- Variable: paragraph-start This is the regular expression for recognizing the beginning of a line that starts *or* separates paragraphs. The default value is `"^[ \t\n\f]"', which matches a line starting with a space, tab, newline, or form feed. -- Variable: sentence-end This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is: "[.?!][]\"')}]*\$$\\|\t\\| \$[ \t\n]*" This means a period, question mark or exclamation mark, followed by a closing brace, followed by tabs, spaces or new lines. For a detailed explanation of this regular expression, see *Note Regexp Example::. File: elisp, Node: Searching and Case, Prev: Standard Regexps, Up: Searching and Matching Searching and Case ================== By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. Regexps, and in particular character sets, are included: thus, `[aB]' would match `a' or `A' or `b' or `B'. If you do not want this feature, set the variable `case-fold-search' to `nil'. Then all letters must match exactly, including case. This is a per-buffer-local variable; altering the variable affects only the current buffer. (*Note Intro to Buffer-Local::.) Alternatively, you may change the value of `default-case-fold-search', which is the default value of `case-fold-search' for buffers that do not override it. -- User Option: case-replace This variable determines whether `query-replace' should preserve case in replacements. If the variable is `nil', then case need not be preserved. -- User Option: case-fold-search This buffer-local variable determines whether searches should ignore case. If the variable is `nil' they do not ignore case; otherwise they do ignore case. -- Variable: default-case-fold-search The value of this variable is the default value for `case-fold-search' in buffers that do not override it. This is the same as `(default-value 'case-fold-search)'. File: elisp, Node: Syntax Tables, Next: Abbrevs, Prev: Searching and Matching, Up: Top Syntax Tables ************* A "syntax table" provides Emacs with the information that determines the syntactic use of each character in a buffer. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. A syntax table is a vector of 256 elements; it contains one entry for each of the 256 ASCII characters of an 8-bit byte. Each element is an integer that encodes the syntax of the character in question. Syntax tables are used only for moving across text, not for the GNU Emacs Lisp reader. GNU Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed. Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character `;' begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to the each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer which uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. *Note Example Major Modes::, for an example of how to set up a syntax table. -- Function: syntax-table-p OBJECT This function returns `t' if OBJECT is a vector of length 256 elements. This means that the vector may be a syntax table. However, according to this test, any vector of length 256 is considered to be a syntax table, no matter what its contents. * Menu: * Syntax Descriptors:: How characters are classified. * Syntax Table Functions:: How to create, examine and alter syntax tables. * Parsing Expressions:: Parsing balanced expressions using the syntax table. * Standard Syntax Tables:: Syntax tables used by various major modes. * Syntax Table Internals:: How syntax table information is stored. File: elisp, Node: Syntax Descriptors, Next: Syntax Table Functions, Prev: Syntax Tables, Up: Syntax Tables Syntax Descriptors ================== This section describes the syntax classes and flags that denote the syntax of a character, and how they are represented as a "syntax descriptor", which is a Lisp string that you pass to `modify-syntax-entry' to specify the desired syntax. Emacs defines twelve "syntax classes". Each syntax table contains a mapping that puts each character into one class. There is no necessary relationship between the class of a character in one syntax table and its class in any other table. Each class is designated by a mnemonic character which serves as the name of the class when you need to specify a class. Usually the designator character is one which is frequently put in that class; however, its meaning as a designator is unvarying and independent of how it is actually classified. A syntax descriptor is a Lisp string which specifies a syntax class, a matching character (unused except for parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient. Thus, the descriptor for the character `*' in C mode is `. 23' (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of an comment-ender), and the entry for `/' is `. 14' (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender). * Menu: * Syntax Class Table:: Table of syntax classes. * Syntax Flags:: Additional flags each character can have.