Info Catalog elisp: String Search elisp: Searching and Matching elisp: Regular Expressions

elisp: Searching and Case

 
 33.2 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.  This applies to regular expressions,
 too; 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 buffer-local variable; altering the variable affects only the current
 buffer.  (Intro to Buffer-Local.)  Alternatively, you may change
 the default value.  In Lisp code, you will more typically use ‘let’ to
 bind ‘case-fold-search’ to the desired value.
 
    Note that the user-level incremental search feature handles case
 distinctions differently.  When the search string contains only lower
 case letters, the search ignores case, but when the search string
 contains one or more upper case letters, the search becomes
 case-sensitive.  But this has nothing to do with the searching functions
 used in Lisp code.  (emacs)Incremental Search.
 
  -- 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 (and by default) they do ignore case.
 
  -- User Option: case-replace
      This variable determines whether the higher-level replacement
      functions should preserve case.  If the variable is ‘nil’, that
      means to use the replacement text verbatim.  A non-‘nil’ value
      means to convert the case of the replacement text according to the
      text being replaced.
 
      This variable is used by passing it as an argument to the function
      ‘replace-match’.  Replacing Match.
 

Info Catalog elisp: String Search elisp: Searching and Matching elisp: Regular Expressions