regexp(n) Tcl Built-In Commands regexp(n) _________________________________________________________________ NAME regexp - Match a regular expression against a string SYNOPSIS regexp ?_s_w_i_t_c_h_e_s? _e_x_p _s_t_r_i_n_g ?_m_a_t_c_h_V_a_r? ?_s_u_b_M_a_t_c_h_V_a_r _s_u_b_- _M_a_t_c_h_V_a_r ...? _________________________________________________________________ DESCRIPTION Determines whether the regular expression _e_x_p matches part or all of _s_t_r_i_n_g and returns 1 if it does, 0 if it doesn't. If additional arguments are specified after _s_t_r_i_n_g then they are treated as the names of variables in which to return information about which part(s) of _s_t_r_i_n_g matched _e_x_p. _M_a_t_c_h_V_a_r will be set to the range of _s_t_r_i_n_g that matched all of _e_x_p. The first _s_u_b_M_a_t_c_h_V_a_r will contain the characters in _s_t_r_i_n_g that matched the leftmost parenthesized subexpres- sion within _e_x_p, the next _s_u_b_M_a_t_c_h_V_a_r will contain the char- acters that matched the next parenthesized subexpression to the right in _e_x_p, and so on. If the initial arguments to regexp start with - then they are treated as switches. The following switches are currently supported: -nocase Causes upper-case characters in _s_t_r_i_n_g to be treated as lower case during the matching process. -indices Changes what is stored in the _s_u_b_M_a_t_c_h_V_a_rs. Instead of storing the matching characters from string, each variable will contain a list of two decimal strings giving the indices in _s_t_r_i_n_g of the first and last characters in the matching range of characters. -- Marks the end of switches. The argument follow- ing this one will be treated as _e_x_p even if it starts with a -. If there are more _s_u_b_M_a_t_c_h_V_a_r's than parenthesized subex- pressions within _e_x_p, or if a particular subexpression in _e_x_p doesn't match the string (e.g. because it was in a por- tion of the expression that wasn't matched), then the corresponding _s_u_b_M_a_t_c_h_V_a_r will be set to ``- 1 - 1'' if - indices has been specified or to an empty string otherwise. Tcl Last change: 1 regexp(n) Tcl Built-In Commands regexp(n) REGULAR EXPRESSIONS Regular expressions are implemented using Henry Spencer's package (thanks, Henry!), and much of the description of regular expressions below is copied verbatim from his manual entry. A regular expression is zero or more _b_r_a_n_c_h_e_s, separated by ``|''. It matches anything that matches one of the branches. A branch is zero or more _p_i_e_c_e_s, concatenated. It matches a match for the first, followed by a match for the second, etc. A piece is an _a_t_o_m possibly followed by ``*'', ``+'', or ``?''. An atom followed by ``*'' matches a sequence of 0 or more matches of the atom. An atom followed by ``+'' matches a sequence of 1 or more matches of the atom. An atom fol- lowed by ``?'' matches a match of the atom, or the null string. An atom is a regular expression in parentheses (matching a match for the regular expression), a _r_a_n_g_e (see below), ``.'' (matching any single character), ``^'' (matching the null string at the beginning of the input string), ``$'' (matching the null string at the end of the input string), a ``\'' followed by a single character (matching that charac- ter), or a single character with no other significance (matching that character). A _r_a_n_g_e is a sequence of characters enclosed in ``[]''. It normally matches any single character from the sequence. If the sequence begins with ``^'', it matches any single char- acter _n_o_t from the rest of the sequence. If two characters in the sequence are separated by ``-'', this is shorthand for the full list of ASCII characters between them (e.g. ``[0-9]'' matches any decimal digit). To include a literal ``]'' in the sequence, make it the first character (follow- ing a possible ``^''). To include a literal ``-'', make it the first or last character. CHOOSING AMONG ALTERNATIVE MATCHES In general there may be more than one way to match a regular expression to an input string. For example, consider the command regexp (a*)b* aabaaabb x y Considering only the rules given so far, x and y could end up with the values aabb and aa, aaab and aaa, ab and a, or any of several other combinations. To resolve this poten- tial ambiguity regexp chooses among alternatives using the rule ``first then longest''. In other words, it considers Tcl Last change: 2 regexp(n) Tcl Built-In Commands regexp(n) the possible matches in order working from left to right across the input string and the pattern, and it attempts to match longer pieces of the input string before shorter ones. More specifically, the following rules apply in decreasing order of priority: [1] If a regular expression could match two different parts of an input string then it will match the one that begins earliest. [2] If a regular expression contains | operators then the leftmost matching sub-expression is chosen. [3] In *, +, and ? constructs, longer matches are chosen in preference to shorter ones. [4] In sequences of expression components the components are considered from left to right. In the example from above, (a*)b* matches aab: the (a*) portion of the pattern is matched first and it consumes the leading aa; then the b* portion of the pattern consumes the next b. Or, consider the following example: regexp (ab|a)(b*)c abc x y z After this command x will be abc, y will be ab, and z will be an empty string. Rule 4 specifies that (ab|a) gets first shot at the input string and Rule 2 specifies that the ab sub-expression is checked before the a sub-expression. Thus the b has already been claimed before the (b*) component is checked and (b*) must match an empty string. KEYWORDS match, regular expression, string Tcl Last change: 3