7.3.4 Regular Expressions in gnatfind and gnatxref

As specified in the section about `gnatfind', the pattern can be a regular expression. Two kinds of regular expressions are recognized:

• `Globbing pattern'

  These are the most common regular expression. They are the same as are generally used in a Unix shell command line, or in a DOS session.

  Here is a more formal grammar:

                regexp ::= term
                term   ::= elmt            -- matches elmt
                term   ::= elmt elmt       -- concatenation (elmt then elmt)
                term   ::= *               -- any string of 0 or more characters
                term   ::= ?               -- matches any character
                term   ::= [char {char}]   -- matches any character listed
                term   ::= [char - char]   -- matches any character in range
  

• `Full regular expression'

  The second set of regular expressions is much more powerful. This is the type of regular expressions recognized by utilities such as grep.

  The following is the form of a regular expression, expressed in same BNF style as is found in the Ada Reference Manual:

                regexp ::= term {| term}   -- alternation (term or term ...)
                
                term ::= item {item}       -- concatenation (item then item)
                
                item ::= elmt              -- match elmt
                item ::= elmt *            -- zero or more elmt's
                item ::= elmt +            -- one or more elmt's
                item ::= elmt ?            -- matches elmt or nothing
                
                elmt ::= nschar            -- matches given character
                elmt ::= [nschar {nschar}]   -- matches any character listed
                elmt ::= [^ nschar {nschar}] -- matches any character not listed
                elmt ::= [char - char]     -- matches chars in given range
                elmt ::= \\ char            -- matches given character
                elmt ::= .                 -- matches any single character
                elmt ::= ( regexp )        -- parens used for grouping
                
                char ::= any character, including special characters
                nschar ::= any character except ()[].*+?^
  

  Here are a few examples:

  abcde|fghi

  will match any of the two strings abcde and fghi,
  

  abc*d

  will match any string like abd, abcd, abccd, abcccd, and so on,
  

  [a-z]+

  will match any string which has only lowercase characters in it (and at least one character.