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Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is incremental; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors.
Besides the usual replace-string command that finds all
occurrences of one string and replaces them with another, Emacs has a
more flexible replacement command called query-replace, which
asks interactively which occurrences to replace. There are also
commands to find and operate on all matches for a pattern.
You can also search multiple files under control of a tags
table (see section Searching and Replacing with Tags Tables) or through the Dired A command
(see section Operating on Files), or ask the grep program to do it
(see section Searching with Grep under Emacs).
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An incremental search begins searching as soon as you type the first character of the search string. As you type in the search string, Emacs shows you where the string (as you have typed it so far) would be found. When you have typed enough characters to identify the place you want, you can stop. Depending on what you plan to do next, you may or may not need to terminate the search explicitly with RET.
Incremental search forward (isearch-forward).
Incremental search backward (isearch-backward).
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C-s starts a forward incremental search. It reads characters from the keyboard, and moves point past the next occurrence of those characters. If you type C-s and then F, that puts the cursor after the first `F' (the first following the starting point, since this is a forward search). Then if you type an O, you will see the cursor move to just after the first `FO' (the `F' in that `FO' may or may not be the first `F'). After another O, the cursor moves to just after the first `FOO' after the place where you started the search. At each step, the buffer text that matches the search string is highlighted, if the terminal can do that; the current search string is always displayed in the echo area.
If you make a mistake in typing the search string, you can cancel characters with DEL. Each DEL cancels the last character of search string. This does not happen until Emacs is ready to read another input character; first it must either find, or fail to find, the character you want to erase. If you do not want to wait for this to happen, use C-g as described below.
When you are satisfied with the place you have reached, you can type RET, which stops searching, leaving the cursor where the search brought it. Also, any command not specially meaningful in searches stops the searching and is then executed. Thus, typing C-a would exit the search and then move to the beginning of the line. RET is necessary only if the next command you want to type is a printing character, DEL, RET, or another character that is special within searches (C-q, C-w, C-r, C-s, C-y, M-y, M-r, M-c, M-e, and some other meta-characters).
When you exit the incremental search, it sets the mark where point was before the search. That is convenient for moving back there. In Transient Mark mode, incremental search sets the mark without activating it, and does so only if the mark is not already active.
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Sometimes you search for `FOO' and find one, but not the one you expected to find. There was a second `FOO' that you forgot about, before the one you were aiming for. In this event, type another C-s to move to the next occurrence of the search string. You can repeat this any number of times. If you overshoot, you can cancel some C-s characters with DEL.
After you exit a search, you can search for the same string again by typing just C-s C-s: the first C-s is the key that invokes incremental search, and the second C-s means "search again."
If a search is failing and you ask to repeat it by typing another C-s, it starts again from the beginning of the buffer. Repeating a failing reverse search with C-r starts again from the end. This is called wrapping around, and `Wrapped' appears in the search prompt once this has happened. If you keep on going past the original starting point of the search, it changes to `Overwrapped', which means that you are revisiting matches that you have already seen.
To reuse earlier search strings, use the search ring. The commands M-p and M-n move through the ring to pick a search string to reuse. These commands leave the selected search ring element in the minibuffer, where you can edit it. To edit the current search string in the minibuffer without replacing it with items from the search ring, type M-e. Type C-s or C-r to terminate editing the string and search for it.
You can change to searching backwards with C-r. For instance, if you are searching forward but you realize you were looking for something above the starting point, you can do this. Repeated C-r keeps looking for more occurrences backwards. A C-s starts going forwards again. C-r in a search can be canceled with DEL.
If you know initially that you want to search backwards, you can use
C-r instead of C-s to start the search, because C-r
as a key runs a command (isearch-backward) to search backward.
A backward search finds matches that end before the starting point,
just as a forward search finds matches that begin after it.
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If your string is not found at all, the echo area says `Failing I-Search'. The cursor is after the place where Emacs found as much of your string as it could. Thus, if you search for `FOOT', and there is no `FOOT', you might see the cursor after the `FOO' in `FOOL'. At this point there are several things you can do. If your string was mistyped, you can rub some of it out and correct it. If you like the place you have found, you can type RET or some other Emacs command to remain there. Or you can type C-g, which removes from the search string the characters that could not be found (the `T' in `FOOT'), leaving those that were found (the `FOO' in `FOOT'). A second C-g at that point cancels the search entirely, returning point to where it was when the search started.
The C-g "quit" character does special things during searches; just what it does depends on the status of the search. If the search has found what you specified and is waiting for input, C-g cancels the entire search. The cursor moves back to where you started the search. If C-g is typed when there are characters in the search string that have not been found--because Emacs is still searching for them, or because it has failed to find them--then the search string characters which have not been found are discarded from the search string. With them gone, the search is now successful and waiting for more input, so a second C-g will cancel the entire search.
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An upper-case letter in the search string makes the search case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. See section Searching and Case.
To search for a newline, type C-j. To search for another control character, such as control-S or carriage return, you must quote it by typing C-q first. This function of C-q is analogous to its use for insertion (see section Inserting Text): it causes the following character to be treated the way any "ordinary" character is treated in the same context. You can also specify a character by its octal code: enter C-q followed by a sequence of octal digits.
M-% typed in incremental search invokes query-replace
or query-replace-regexp (depending on search mode) with the
current search string used as the string to replace. See section Query Replace.
Entering RET when the search string is empty launches nonincremental search (see section Nonincremental Search).
To customize the special characters that incremental search understands,
alter their bindings in the keymap isearch-mode-map. For a list
of bindings, look at the documentation of isearch-mode with
C-h f isearch-mode RET.
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To enter non-ASCII characters in an incremental search, you can use C-q (see the previous section), but it is easier to use an input method (see section Input Methods). If an input method is enabled in the current buffer when you start the search, you can use it in the search string also. Emacs indicates that by including the input method mnemonic in its prompt, like this:
I-search [im]: |
where im is the mnemonic of the active input method.
You can toggle (enable or disable) the input method while you type
the search string with C-\ (isearch-toggle-input-method).
You can turn on a certain (non-default) input method with C-^
(isearch-toggle-specified-input-method), which prompts for the
name of the input method. The input method you enable during
incremental search remains enabled in the current buffer afterwards.
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The characters C-w and C-y can be used in incremental search to grab text from the buffer into the search string. This makes it convenient to search for another occurrence of text at point. C-w copies the character or word after point as part of the search string, advancing point over it. (The decision, whether to copy a character or a word, is heuristic.) Another C-s to repeat the search will then search for a string including that character or word.
C-y is similar to C-w but copies all the rest of the current line into the search string. If point is already at the end of a line, it grabs the entire next line. Both C-y and C-w convert the text they copy to lower case if the search is currently not case-sensitive; this is so the search remains case-insensitive.
C-M-w and C-M-y modify the search string by only one character at a time: C-M-w deletes the last character from the search string and C-M-y copies the character after point to the end of the search string. An alternative method to add the character after point into the search string is to enter the minibuffer by M-e and to type C-f at the end of the search string in the minibuffer.
The character M-y copies text from the kill ring into the search string. It uses the same text that C-y as a command would yank. Mouse-2 in the echo area does the same. See section Yanking.
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When you pause for a little while during incremental search, it
highlights all other possible matches for the search string. This
makes it easier to anticipate where you can get to by typing C-s
or C-r to repeat the search. The short delay before highlighting
other matches helps indicate which match is the current one.
If you don't like this feature, you can turn it off by setting
isearch-lazy-highlight to nil.
You can control how this highlighting looks by customizing the faces
isearch (used for the current match) and lazy-highlight
(for all the other matches).
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You can enable the use of vertical scrolling during incremental
search (without exiting the search) by setting the customizable
variable isearch-allow-scroll to a non-nil value. This
applies to using the vertical scroll-bar and to certain keyboard
commands such as PRIOR (scroll-down),
NEXT (scroll-up) and C-l (recenter).
You must run these commands via their key sequences to stay in the
search--typing M-x will terminate the search. You can give
prefix arguments to these commands in the usual way.
This feature won't let you scroll the current match out of visibility, however.
The feature also affects some other commands, such as C-x 2
(split-window-vertically) and C-x ^
(enlarge-window) which don't exactly scroll but do affect where
the text appears on the screen. In general, it applies to any command
whose name has a non-nil isearch-scroll property. So you
can control which commands are affected by changing these properties.
For example, to make C-h l usable within an incremental search
in all future Emacs sessions, use C-h c to find what command it
runs. (You type C-h c C-h l; it says view-lossage.)
Then you can put the following line in your `.emacs' file
(see section The Init File, `~/.emacs'):
(put 'view-lossage 'isearch-scroll t) |
This feature can be applied to any command that doesn't permanently change point, the buffer contents, the match data, the current buffer, or the selected window and frame. The command must not itself attempt an incremental search.
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Incremental search on a slow terminal uses a modified style of display that is designed to take less time. Instead of redisplaying the buffer at each place the search gets to, it creates a new single-line window and uses that to display the line that the search has found. The single-line window comes into play as soon as point moves outside of the text that is already on the screen.
When you terminate the search, the single-line window is removed. Emacs then redisplays the window in which the search was done, to show its new position of point.
The slow terminal style of display is used when the terminal baud rate is
less than or equal to the value of the variable search-slow-speed,
initially 1200. See also the discussion of the variable baud-rate
(see Customization of Display).
The number of lines to use in slow terminal search display is controlled
by the variable search-slow-window-lines. Its normal value is 1.
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Emacs also has conventional nonincremental search commands, which require you to type the entire search string before searching begins.
Search for string.
Search backward for string.
To do a nonincremental search, first type C-s RET. This enters the minibuffer to read the search string; terminate the string with RET, and then the search takes place. If the string is not found, the search command signals an error.
When you type C-s RET, the C-s invokes incremental
search as usual. That command is specially programmed to invoke
nonincremental search, search-forward, if the string you
specify is empty. (Such an empty argument would otherwise be
useless.) But it does not call search-forward right away. First
it checks the next input character to see if is C-w,
which specifies a word search.
See section Word Search.
C-r RET does likewise, for a reverse incremental search.
Forward and backward nonincremental searches are implemented by the
commands search-forward and search-backward. These
commands may be bound to keys in the usual manner. The feature that you
can get to them via the incremental search commands exists for
historical reasons, and to avoid the need to find separate key sequences
for them.
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Word search searches for a sequence of words without regard to how the words are separated. More precisely, you type a string of many words, using single spaces to separate them, and the string can be found even if there are multiple spaces, newlines, or other punctuation characters between these words.
Word search is useful for editing a printed document made with a text formatter. If you edit while looking at the printed, formatted version, you can't tell where the line breaks are in the source file. With word search, you can search without having to know them.
Search for words, ignoring details of punctuation.
Search backward for words, ignoring details of punctuation.
Word search as a special case of nonincremental search is invoked with C-s RET C-w. This is followed by the search string, which must always be terminated with RET. Being nonincremental, this search does not start until the argument is terminated. It works by constructing a regular expression and searching for that; see Regular Expression Search.
Use C-r RET C-w to do backward word search.
You can also invoke word search with C-s M-e C-w or C-r M-e C-w followed by the search string and terminated with RET, C-s or C-r. This puts word search into incremental mode where you can use all keys available for incremental search. However, when you type more words in incremental word search, it will fail until you type complete words.
Forward and backward word searches are implemented by the commands
word-search-forward and word-search-backward. These
commands may be bound to keys in the usual manner. They are available
via the incremental search commands both for historical reasons and
to avoid the need to find separate key sequences for them.
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A regular expression (regexp, for short) is a pattern that denotes a class of alternative strings to match, possibly infinitely many. GNU Emacs provides both incremental and nonincremental ways to search for a match for a regexp. The syntax of regular expressions is explained in the following section.
Incremental search for a regexp is done by typing C-M-s
(isearch-forward-regexp), by invoking C-s with a
prefix argument (whose value does not matter), or by typing M-r
within a forward incremental search. This command reads a
search string incrementally just like C-s, but it treats the
search string as a regexp rather than looking for an exact match
against the text in the buffer. Each time you add text to the search
string, you make the regexp longer, and the new regexp is searched
for. To search backward for a regexp, use C-M-r
(isearch-backward-regexp), C-r with a prefix argument,
or M-r within a backward incremental search.
All of the control characters that do special things within an ordinary incremental search have the same function in incremental regexp search. Typing C-s or C-r immediately after starting the search retrieves the last incremental search regexp used; that is to say, incremental regexp and non-regexp searches have independent defaults. They also have separate search rings that you can access with M-p and M-n.
If you type SPC in incremental regexp search, it matches any
sequence of whitespace characters, including newlines. If you want to
match just a space, type C-q SPC. You can control what a
bare space matches by setting the variable
search-whitespace-regexp to the desired regexp.
In some cases, adding characters to the regexp in an incremental regexp search can make the cursor move back and start again. For example, if you have searched for `foo' and you add `\|bar', the cursor backs up in case the first `bar' precedes the first `foo'.
Forward and backward regexp search are not symmetrical, because regexp matching in Emacs always operates forward, starting with the beginning of the regexp. Thus, forward regexp search scans forward, trying a forward match at each possible starting position. Backward regexp search scans backward, trying a forward match at each possible starting position. These search methods are not mirror images.
Nonincremental search for a regexp is done by the functions
re-search-forward and re-search-backward. You can invoke
these with M-x, or bind them to keys, or invoke them by way of
incremental regexp search with C-M-s RET and C-M-r
RET.
If you use the incremental regexp search commands with a prefix
argument, they perform ordinary string search, like
isearch-forward and isearch-backward. See section Incremental Search.
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This manual describes regular expression features that users typically want to use. There are additional features that are mainly used in Lisp programs; see (elisp)Regular Expressions section `Regular Expressions' in The Emacs Lisp Reference Manual.
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 same character and nothing else. The special characters are `$', `^', `.', `*', `+', `?', `[', and `\'. The character `]' is special if it ends a character alternative (see later). The character `-' is special inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it. (When you use regular expressions in a Lisp program, each `\' must be doubled, see the example near the end of this section.)
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'. (When case distinctions are being ignored, these regexps also match `F' and `O', but we consider this a generalization of "the same string," rather than an exception.)
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 nontrivial, you need to use one of the special characters. Here is a list of them.
is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like `a.b', which matches any three-character string that begins with `a' and ends with `b'.
is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, `o*' matches any number of `o's (including no `o's).
`*' always applies to the smallest possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. It matches `f', `fo', `foo', and so on.
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, in matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully.
is a postfix operator, similar to `*' except that it must match the preceding expression at least once. So, for example, `ca+r' matches the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' matches all three strings.
is a postfix operator, similar to `*' except that it can match the preceding expression either once or not at all. For example, `ca?r' matches `car' or `cr'; nothing else.
are non-greedy variants of the operators above. The normal operators `*', `+', `?' are greedy in that they match as much as they can, as long as the overall regexp can still match. With a following `?', they are non-greedy: they will match as little as possible.
Thus, both `ab*' and `ab*?' can match the string `a' and the string `abbbb'; but if you try to match them both against the text `abbb', `ab*' will match it all (the longest valid match), while `ab*?' will match just `a' (the shortest valid match).
Non-greedy operators match the shortest possible string starting at a given starting point; in a forward search, though, the earliest possible starting point for match is always the one chosen. Thus, if you search for `a.*?$' against the text `abbab' followed by a newline, it matches the whole string. Since it can match starting at the first `a', it does.
is a postfix operator that specifies repetition n times--that is, the preceding regular expression must match exactly n times in a row. For example, `x\{4\}' matches the string `xxxx' and nothing else.
is a postfix operator that specifies repetition between n and
m times--that is, the preceding regular expression must match
at least n times, but no more than m times. If m is
omitted, then there is no upper limit, but the preceding regular
expression must match at least n times.
`\{0,1\}' is
equivalent to `?'.
`\{0,\}' is equivalent to
`*'.
`\{1,\}' is equivalent to `+'.
is a character set, which begins with `[' and is terminated by `]'. In the simplest case, the characters between the two brackets are what this set can match.
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.
You can also include character ranges in a character set, by writing the starting and ending characters with a `-' between them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower-case ASCII letter or `$', `%' or period.
Note that the usual regexp special characters are not special inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'.
To include a `]' in a character set, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character of the set, or put it after a range. Thus, `[]-]' matches both `]' and `-'.
To include `^' in a set, put it anywhere but at the beginning of the set. (At the beginning, it complements the set--see below.)
When you use a range in case-insensitive search, you should write both ends of the range in upper case, or both in lower case, or both should be non-letters. The behavior of a mixed-case range such as `A-z' is somewhat ill-defined, and it may change in future Emacs versions.
`[^' begins a complemented character set, which matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters except ASCII 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 (in other words, `-' and `]' are not special there).
A complemented character set can match a newline, unless newline is
mentioned as one of the characters not to match. This is in contrast to
the handling of regexps in programs such as grep.
is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, `^foo' matches a `foo' that occurs at the beginning of a line.
For historical compatibility reasons, `^' can be used with this meaning only at the beginning of the regular expression, or after `\(' or `\|'.
is similar to `^' but matches only at the end of a line. Thus, `x+$' matches a string of one `x' or more at the end of a line.
For historical compatibility reasons, `$' can be used with this meaning only at the end of the regular expression, or before `\)' or `\|'.
has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs.
Because `\' quotes special characters, `\$' is a regular expression that matches only `$', and `\[' is a regular expression that matches only `[', and so on.
See the following section for the special constructs that begin with `\'.
Note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; it is better to quote the special character anyway, regardless of where it appears.
As a `\' is not special inside a character alternative, it can
never remove the special meaning of `-' or `]'. So you
should not quote these characters when they have no special meaning
either. This would not clarify anything, since backslashes can
legitimately precede these characters where they have special
meaning, as in `[^\]' ("[^\\]" for Lisp string syntax),
which matches any single character except a backslash.
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For the most part, `\' followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with `\' that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of `\' constructs.
specifies an alternative. Two regular expressions a and b with `\|' in between form an expression that matches some text if either a matches it or b matches it. It works by trying to match a, and if that fails, by trying to match b.
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:
To enclose a set of `\|' alternatives for other operations. Thus, `\(foo\|bar\)x' matches either `foox' or `barx'.
To enclose a complicated expression for the postfix operators `*', `+' and `?' to operate on. Thus, `ba\(na\)*' matches `bananana', etc., with any (zero or more) number of `na' strings.
To record a matched substring for future reference.
This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same `\( … \)' construct. In practice there is usually no conflict between the two meanings; when there is a conflict, you can use a "shy" group.
specifies a "shy" group that does not record the matched substring; you can't refer back to it with `\d'. This is useful in mechanically combining regular expressions, so that you can add groups for syntactic purposes without interfering with the numbering of the groups that are meant to be referred to.
matches the same text that matched the dth occurrence of a `\( … \)' construct. This is called a back reference.
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 the digit d to mean "match the same text matched the dth 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. So you can use `\1' through `\9' to refer to the text matched by the corresponding `\( … \)' constructs.
For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text.
If a particular `\( … \)' construct matches more than once (which can easily happen if it is followed by `*'), only the last match is recorded.
matches the empty string, but only at the beginning of the string or buffer (or its accessible portion) being matched against.
matches the empty string, but only at the end of the string or buffer (or its accessible portion) being matched against.
matches the empty string, but only at point.
matches the empty string, but only at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word.
`\b' matches at the beginning or end of the buffer regardless of what text appears next to it.
matches the empty string, but not at the beginning or end of a word.
matches the empty string, but only at the beginning of a word. `\<' matches at the beginning of the buffer only if a word-constituent character follows.
matches the empty string, but only at the end of a word. `\>' matches at the end of the buffer only if the contents end with a word-constituent character.
matches any word-constituent character. The syntax table determines which characters these are. See section The Syntax Table.
matches any character that is not a word-constituent.
matches the empty string, but only at the beginning of a symbol. A symbol is a sequence of one or more symbol-constituent characters. A symbol-constituent character is a character whose syntax is either `w' or `_'. `\_<' matches at the beginning of the buffer only if a symbol-constituent character follows.
matches the empty string, but only at the end of a symbol. `\_>' matches at the end of the buffer only if the contents end with a symbol-constituent character.
matches any character whose syntax is c. Here c is a character that designates a particular syntax class: thus, `w' for word constituent, `-' or ` ' for whitespace, `.' for ordinary punctuation, etc. See section The Syntax Table.
matches any character whose syntax is not c.
matches any character that belongs to the category c. For example, `\cc' matches Chinese characters, `\cg' matches Greek characters, etc. For the description of the known categories, type M-x describe-categories RET.
matches any character that does not belong to category c.
The constructs that pertain to words and syntax are controlled by the setting of the syntax table (see section The Syntax Table).
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Here is a complicated regexp--a simplified version of the regexp that Emacs uses, by default, to recognize the end of a sentence together with any whitespace that follows. We show its Lisp syntax to distinguish the spaces from the tab characters. In Lisp syntax, the string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the regexp, `\\' for a backslash as part of the regexp, `\t' for a tab, and `\n' for a newline.
"[.?!][]\"')]*\\($\\| $\\|\t\\| \\)[ \t\n]*" |
This contains four parts in succession: a character set matching period, `?', or `!'; a character set matching close-brackets, quotes, or parentheses, repeated zero or more times; a set of alternatives within backslash-parentheses that matches either end-of-line, a space at the end of a line, a tab, or two spaces; and a character set matching whitespace characters, repeated any number of times.
To enter the same regexp in incremental search, you would type TAB to enter a tab, and C-j to enter a newline. You would also type single backslashes as themselves, instead of doubling them for Lisp syntax. In commands that use ordinary minibuffer input to read a regexp, you would quote the C-j by preceding it with a C-q to prevent C-j from exiting the minibuffer.
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Incremental searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for `foo', then `Foo' and `foo' are also considered a match. Regexps, and in particular character sets, are included: `[ab]' would match `a' or `A' or `b' or `B'.
An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for `Foo' does not find `foo' or `FOO'. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string.
Typing M-c within an incremental search toggles the case sensitivity of that search. The effect does not extend beyond the current incremental search to the next one, but it does override the effect of including an upper-case letter in the current search.
If you set the variable case-fold-search to nil, then
all letters must match exactly, including case. This is a per-buffer
variable; altering the variable affects only the current buffer, but
there is a default value in default-case-fold-search that you
can also set. See section Local Variables. This variable applies to nonincremental
searches also, including those performed by the replace commands
(see section Replacement Commands) and the minibuffer history matching commands
(see section Minibuffer History).
Several related variables control case-sensitivity of searching and
matching for specific commands or activities. For instance,
tags-case-fold-search controls case sensitivity for
find-tag. To find these variables, do M-x
apropos-variable RET case-fold-search RET.
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Global search-and-replace operations are not needed often in Emacs,
but they are available. In addition to the simple M-x
replace-string command which replaces all occurrences,
there is M-% (query-replace), which presents each occurrence
of the pattern and asks you whether to replace it.
The replace commands normally operate on the text from point to the
end of the buffer; however, in Transient Mark mode (see section Transient Mark Mode), when the mark is active, they operate on the region. The
basic replace commands replace one string (or regexp) with one
replacement string. It is possible to perform several replacements in
parallel using the command expand-region-abbrevs
(see section Controlling Abbrev Expansion).
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Replace every occurrence of string with newstring.
To replace every instance of `foo' after point with `bar', use the command M-x replace-string with the two arguments `foo' and `bar'. Replacement happens only in the text after point, so if you want to cover the whole buffer you must go to the beginning first. All occurrences up to the end of the buffer are replaced; to limit replacement to part of the buffer, narrow to that part of the buffer before doing the replacement (see section Narrowing). In Transient Mark mode, when the region is active, replacement is limited to the region (see section Transient Mark Mode).
When replace-string exits, it leaves point at the last
occurrence replaced. It sets the mark to the prior position of point
(where the replace-string command was issued); use C-u
C-SPC to move back there.
A numeric argument restricts replacement to matches that are surrounded by word boundaries. The argument's value doesn't matter.
See section Replace Commands and Case, for details about case-sensitivity in replace commands.
What if you want to exchange `x' and `y': replace every `x' with a `y' and vice versa? You can do it this way:
M-x replace-string RET x RET @TEMP@ RET M-< M-x replace-string RET y RET x RET M-< M-x replace-string RET @TEMP@ RET y RET |
This works provided the string `@TEMP@' does not appear in your text.
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The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.
Replace every match for regexp with newstring.
In replace-regexp, the newstring need not be constant:
it can refer to all or part of what is matched by the regexp.
`\&' in newstring stands for the entire match being
replaced. `\d' in newstring, where d is a
digit, stands for whatever matched the dth parenthesized
grouping in regexp. (This is called a "back reference.")
`\#' refers to the count of replacements already made in this
command, as a decimal number. In the first replacement, `\#'
stands for `0'; in the second, for `1'; and so on. For
example,
M-x replace-regexp RET c[ad]+r RET \&-safe RET |
replaces (for example) `cadr' with `cadr-safe' and `cddr' with `cddr-safe'.
M-x replace-regexp RET \(c[ad]+r\)-safe RET \1 RET |
performs the inverse transformation. To include a `\' in the text to replace with, you must enter `\\'.
If you want to enter part of the replacement string by hand each time, use `\?' in the replacement string. Each replacement will ask you to edit the replacement string in the minibuffer, putting point where the `\?' was.
The remainder of this subsection is intended for specialized tasks and requires knowledge of Lisp. Most readers can skip it.
You can use Lisp expressions to calculate parts of the replacement string. To do this, write `\,' followed by the expression in the replacement string. Each replacement calculates the value of the expression and converts it to text without quoting (if it's a string, this means using the string's contents), and uses it in the replacement string in place of the expression itself. If the expression is a symbol, one space in the replacement string after the symbol name goes with the symbol name, so the value replaces them both.
Inside such an expression, you can use some special sequences.
`\&' and `\n' refer here, as usual, to the entire
match as a string, and to a submatch as a string. n may be
multiple digits, and the value of `\n' is nil if
subexpression n did not match. You can also use `\#&' and
`\#n' to refer to those matches as numbers (this is valid
when the match or submatch has the form of a numeral). `\#' here
too stands for the number of already-completed replacements.
Repeating our example to exchange `x' and `y', we can thus do it also this way:
M-x replace-regexp RET \(x\)\|y RET \,(if \1 "y" "x") RET |
For computing replacement strings for `\,', the format
function is often useful (see (elisp)Formatting Strings section `Formatting Strings' in The Emacs Lisp Reference Manual). For example, to add consecutively numbered
strings like `ABC00042' to columns 73 to 80 (unless they are
already occupied), you can use
M-x replace-regexp RET ^.\{0,72\}$ RET
\,(format "%-72sABC%05d" \& \#) RET
|
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If the first argument of a replace command is all lower case, the
command ignores case while searching for occurrences to
replace--provided case-fold-search is non-nil. If
case-fold-search is set to nil, case is always significant
in all searches.
In addition, when the newstring argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command
M-x replace-string RET foo RET bar RET |
replaces a lower case `foo' with a lower case `bar', an
all-caps `FOO' with `BAR', and a capitalized `Foo' with
`Bar'. (These three alternatives--lower case, all caps, and
capitalized, are the only ones that replace-string can
distinguish.)
If upper-case letters are used in the replacement string, they remain
upper case every time that text is inserted. If upper-case letters are
used in the first argument, the second argument is always substituted
exactly as given, with no case conversion. Likewise, if either
case-replace or case-fold-search is set to nil,
replacement is done without case conversion.
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Replace some occurrences of string with newstring.
Replace some matches for regexp with newstring.
If you want to change only some of the occurrences of `foo' to
`bar', not all of them, then you cannot use an ordinary
replace-string. Instead, use M-% (query-replace).
This command finds occurrences of `foo' one by one, displays each
occurrence and asks you whether to replace it. Aside from querying,
query-replace works just like replace-string. It
preserves case, like replace-string, provided
case-replace is non-nil, as it normally is
(see section Replace Commands and Case). A numeric argument means consider
only occurrences that are bounded by word-delimiter characters.
C-M-% performs regexp search and replace (query-replace-regexp).
It works like replace-regexp except that it queries
like query-replace.
These commands highlight the current match using the face
query-replace. They highlight other matches using
lazy-highlight just like incremental search (see section Incremental Search).
The characters you can type when you are shown a match for the string or regexp are:
to replace the occurrence with newstring.
to skip to the next occurrence without replacing this one.
to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, DEL and SPC are equivalent in this situation; both move to the next occurrence.
You can type C-r at this point (see below) to alter the replaced
text. You can also type C-x u to undo the replacement; this exits
the query-replace, so if you want to do further replacement you
must use C-x ESC ESC RET to restart
(see section Repeating Minibuffer Commands).
to exit without doing any more replacements.
to replace this occurrence and then exit without searching for more occurrences.
to replace all remaining occurrences without asking again.
to go back to the position of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake or want to reexamine it.
to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with newstring. When you are done, exit the recursive editing level with C-M-c to proceed to the next occurrence. See section Recursive Editing Levels.
to delete the occurrence, and then enter a recursive editing level as in C-r. Use the recursive edit to insert text to replace the deleted occurrence of string. When done, exit the recursive editing level with C-M-c to proceed to the next occurrence.
to edit the replacement string in the minibuffer. When you exit the minibuffer by typing RET, the minibuffer contents replace the current occurrence of the pattern. They also become the new replacement string for any further occurrences.
to redisplay the screen. Then you must type another character to specify what to do with this occurrence.
to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence.
Some other characters are aliases for the ones listed above: y, n and q are equivalent to SPC, DEL and RET.
Aside from this, any other character exits the query-replace,
and is then reread as part of a key sequence. Thus, if you type
C-k, it exits the query-replace and then kills to end of
line.
To restart a query-replace once it is exited, use C-x
ESC ESC, which repeats the query-replace because it
used the minibuffer to read its arguments. See section C-x ESC ESC.
See section Operating on Files, for the Dired Q command which performs query replace on selected files. See also Transforming File Names in Dired, for Dired commands to rename, copy, or link files by replacing regexp matches in file names.
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Here are some other commands that find matches for a regular
expression. They all ignore case in matching, if the pattern contains
no upper-case letters and case-fold-search is non-nil.
Aside from occur and its variants, all operate on the text from
point to the end of the buffer, or on the active region in Transient
Mark mode.
Display a list showing each line in the buffer that contains a match
for regexp. To limit the search to part of the buffer, narrow
to that part (see section Narrowing). A numeric argument n
specifies that n lines of context are to be displayed before and
after each matching line. Currently, occur can not correctly
handle multiline matches.
The buffer `*Occur*' containing the output serves as a menu for finding the occurrences in their original context. Click Mouse-2 on an occurrence listed in `*Occur*', or position point there and type RET; this switches to the buffer that was searched and moves point to the original of the chosen occurrence. o and C-o display the match in another window; C-o does not select it.
After using M-x occur, you can use next-error to visit
the occurrences found, one by one. Compilation Mode.
Synonym for M-x occur.
This function is just like occur, except it is able to search
through multiple buffers. It asks you to specify the buffer names one by one.
This function is similar to multi-occur, except the buffers to
search are specified by a regular expression that matches visited
file names. With a prefix argument, it uses the regular expression to match
buffer names instead.
Print the number of matches for regexp that exist in the buffer after point. In Transient Mark mode, if the region is active, the command operates on the region instead.
This command deletes each line that contains a match for regexp, operating on the text after point; it deletes the current line if it contains a match starting after point. In Transient Mark mode, if the region is active, the command operates on the region instead; it deletes a line partially contained in the region if it contains a match entirely contained in the region.
If a match is split across lines, flush-lines deletes all those
lines. It deletes the lines before starting to look for the next
match; hence, it ignores a match starting on the same line at which
another match ended.
This command deletes each line that does not contain a match for regexp, operating on the text after point; if point is not at the beginning of a line, it always keeps the current line. In Transient Mark mode, if the region is active, the command operates on the region instead; it never deletes lines that are only partially contained in the region (a newline that ends a line counts as part of that line).
If a match is split across lines, this command keeps all those lines.
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