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31.2 Examining Buffer Contents

This section describes functions that allow a Lisp program to convert any portion of the text in the buffer into a string.

Function: buffer-substring start end

This function returns a string containing a copy of the text of the region defined by positions start and end in the current buffer. If the arguments are not positions in the accessible portion of the buffer, buffer-substring signals an args-out-of-range error.

Here’s an example which assumes Font-Lock mode is not enabled:

---------- Buffer: foo ----------
This is the contents of buffer foo

---------- Buffer: foo ----------

(buffer-substring 1 10)
     ⇒ "This is t"
(buffer-substring (point-max) 10)
     ⇒ "he contents of buffer foo\n"

If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See Text Properties. However, overlays (see Overlays) in the buffer and their properties are ignored, not copied.

For example, if Font-Lock mode is enabled, you might get results like these:

(buffer-substring 1 10)
     ⇒ #("This is t" 0 1 (fontified t) 1 9 (fontified t))
Function: buffer-substring-no-properties start end

This is like buffer-substring, except that it does not copy text properties, just the characters themselves. See Text Properties.

Function: buffer-string

This function returns the contents of the entire accessible portion of the current buffer, as a string.

Function: filter-buffer-substring start end &optional delete

This function filters the buffer text between start and end using a function specified by the variable filter-buffer-substring-function, and returns the result.

The default filter function consults the obsolete wrapper hook filter-buffer-substring-functions, and the obsolete variable buffer-substring-filters. If both of these are nil, it returns the unaltered text from the buffer, i.e., what buffer-substring would return.

If delete is non-nil, the function deletes the text between start and end after copying it, like delete-and-extract-region.

Lisp code should use this function instead of buffer-substring, buffer-substring-no-properties, or delete-and-extract-region when copying into user-accessible data structures such as the kill-ring, X clipboard, and registers. Major and minor modes can modify filter-buffer-substring-function to alter such text as it is copied out of the buffer.

Variable: filter-buffer-substring-function

The value of this variable is a function that filter-buffer-substring will call to do the actual work. The function receives three arguments, the same as those of filter-buffer-substring, which it should treat as per the documentation of that function. It should return the filtered text (and optionally delete the source text).

The following two variables are obsoleted by filter-buffer-substring-function, but are still supported for backward compatibility.

Variable: filter-buffer-substring-functions

This obsolete variable is a wrapper hook, whose members should be functions that accept four arguments: fun, start, end, and delete. fun is a function that takes three arguments (start, end, and delete), and returns a string. In both cases, the start, end, and delete arguments are the same as those of filter-buffer-substring.

The first hook function is passed a fun that is equivalent to the default operation of filter-buffer-substring, i.e., it returns the buffer-substring between start and end (processed by any buffer-substring-filters) and optionally deletes the original text from the buffer. In most cases, the hook function will call fun once, and then do its own processing of the result. The next hook function receives a fun equivalent to this, and so on. The actual return value is the result of all the hook functions acting in sequence.

Variable: buffer-substring-filters

The value of this obsolete variable should be a list of functions that accept a single string argument and return another string. The default filter-buffer-substring function passes the buffer substring to the first function in this list, and the return value of each function is passed to the next function. The return value of the last function is passed to filter-buffer-substring-functions.

Function: current-word &optional strict really-word

This function returns the symbol (or word) at or near point, as a string. The return value includes no text properties.

If the optional argument really-word is non-nil, it finds a word; otherwise, it finds a symbol (which includes both word characters and symbol constituent characters).

If the optional argument strict is non-nil, then point must be in or next to the symbol or word—if no symbol or word is there, the function returns nil. Otherwise, a nearby symbol or word on the same line is acceptable.

Function: thing-at-point thing

Return the thing around or next to point, as a string.

The argument thing is a symbol which specifies a kind of syntactic entity. Possibilities include symbol, list, sexp, defun, filename, url, word, sentence, whitespace, line, page, and others.

---------- Buffer: foo ----------
Gentlemen may cry ``Pea∗ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------

(thing-at-point 'word)
     ⇒ "Peace"
(thing-at-point 'line)
     ⇒ "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
     ⇒ nil

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