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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.
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.
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.
matches any word-constituent character. The editor syntax table
determines which characters these are. *Note Syntax Tables::.
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.