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Unix find tutorial

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Part 3: Finding files using file name or path

Find development processes thru several generations and each left certain mark on its ability to use regular expressions. As of August 2009 it still cannot use Perl regular expression, though.

• Name predicate and shell patterns
• Searching fully qualified file name and path
• Regular expressions

Name predicate and shell patterns

          find /etc -name '*.conf'

Note: To ignore a subtree you can use ‘-prune’ .

Searching fully qualified file name and path

In the context of the tests ‘-path’, ‘-wholename’, ‘-ipath’ and ‘-wholename’, a “ path” is consists of all the directories traversed from find's start point to the file being tested, followed by the base name of the file itself. These paths are often not absolute paths; for example

     cd /tmp
     mkdir -p foo/bar/baz
     find foo -path foo/bar -print foo/bar # first find command
     find foo -path /tmp/foo/bar -print # the second find command (prints nothing)
     find /tmp/foo -path /tmp/foo/bar -print /tmp/foo/bar # the third find command

Notice that due to search starting point foo the second find command prints nothing, even though /tmp/foo/bar exists.

Unlike file name expansion on the command line, a ‘*’ in the pattern will match both ‘/’ and leading dots in file names:

     $ find .  -path '*f'
     ./quux/bar/baz/f
     $ find .  -path '*/*config'
     ./quux/bar/baz/.config

Regular expressions

Type of regular expression can be specified with option -regextype. In best GNU traditions you need to select from several option only half of which are useful

• ‘posix-extended’  POSIX Extended Regular Expressions. Makes most sense. 
• ‘emacs’ Default behavior, useful to users of Emacs.
• ‘posix-awk’  Regular expressions compatible with the POSIX awk command (not GNU awk). Useful for heavy awk users
  • The character ‘.’ matches any single character except the null character.
  • ‘+’ indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
  • ‘?’ indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
  • ‘\+’ matches a ‘+’
  • ‘\?’ matches a ‘?’.
• ‘posix-basic’ POSIX Basic Regular Expressions. It's probably the most popular type often called shell patterns and used by default in -name predicate
  • * Matches any zero or more characters.
  • ? Matches any one character.
  • [string] Matches exactly one character that is a member of the string string. This is called a character class. As a shorthand, string may contain ranges, which consist of two characters with a dash between them. For example, the class ‘[a-z0-9_]’ matches a lowercase letter, a number, or an underscore. You can negate a class by placing a ‘!’ or ‘^’ immediately after the opening bracket. Thus, ‘[^A-Z@]’ matches any character except an uppercase letter or an at sign.
  • \ Removes the special meaning of the character that follows it. This works even in character classes
• ‘posix-egrep’ Regular expressions compatible with the POSIX egrep command

  See Regular Expressions for more information on the regular expression dialects...

  The regular expression itself can be specified using -regex option (or -iregex option which ignores case). You must quote patterns that contain metacharacters to prevent the shell from expanding them itself. Double and single quotes both work; so does escaping with a backslash.

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