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Info file elisp, produced by Makeinfo, -*- Text -*- from 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: Indent Tabs, Next: Motion by Indent, Prev: Relative Indent, Up: Indentation
Adjustable "Tab Stops"
----------------------
This section explains the mechanism for user-specified "tab stops"
and the mechanisms which use and set them. The name "tab stops" is
used because the feature is similar to that of the tab stops on a
typewriter. The feature works by inserting an appropriate number of
spaces and tab characters to reach the designated position, like the
other indentation functions; it does not affect the display of tab
characters in the buffer (*note Control Char Display::.). Note that
the TAB character as input uses this tab stop feature only in a few
major modes, such as Text mode.
* Function: tab-to-tab-stop
This function inserts spaces or tabs up to the next tab stop
column defined by `tab-stop-list'. It searches the list for an
element greater than the current column number, and uses that
element as the column to indent to. If no such element is
found, then nothing is done.
* User Option: tab-stop-list
This variable is the list of tab stop columns used by
`tab-to-tab-stops'. The elements should be integers in
increasing order. The tab stop columns need not be evenly spaced.
Use `M-x edit-tab-stops' to edit the location of tab stops
interactively.
File: elisp, Node: Motion by Indent, Prev: Indent Tabs, Up: Indentation
Indentation-Based Motion Commands
---------------------------------
These commands, primarily for interactive use, act based on the
indentation in the text.
* Command: back-to-indentation
This command moves point to the first non-whitespace character
in the current line (which is the line in which point is
located). It returns `nil'.
* Command: backward-to-indentation ARG
This command moves point backward ARG lines and then to the
first nonblank character on that line. It returns `nil'.
* Command: forward-to-indentation ARG
This command moves point forward ARG lines and then to the first
nonblank character on that line. It returns `nil'.
File: elisp, Node: Columns, Next: Case Changes, Prev: Indentation, Up: Text
Counting Columns
================
The column functions convert between a character position
(counting characters from the beginning of the buffer) and a column
position (counting screen characters from the beginning of a line).
Column number computations ignore the width of the window and the
amount of horizontal scrolling. Consequently, a column value can be
arbitrarily high. The first (or leftmost) column is numbered 0.
A character counts according to the number of columns it occupies
on the screen. This means control characters count as occupying 2 or
4 columns, depending upon the value of `ctl-arrow', and tabs count as
occupying a number of columns that depends on the value of
`tab-width' and on the column where the tab begins. *Note Control
Char Display::.
* Function: current-column
This function returns the horizontal position of point, measured
in columns, counting from 0 at the left margin. The column
count is calculated by adding together the widths of all the
displayed representations of the characters between the start of
the current line and point.
For a more complicated example of the use of `current-column',
see the description of `count-lines' in *Note Text Lines::.
* Function: move-to-column COLUMN
This function moves point to COLUMN in the current line. The
calculation of COLUMN takes into account the widths of all the
displayed representations of the characters between the start of
the line and point.
If the argument COLUMN is greater than the column position of
the end of the line, point moves to the end of the line. If
COLUMN is negative, point moves to the beginning of the line.
An error is signaled if COLUMN is not an integer.
The return value is the column number actually moved to.
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 : (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)'.