REGEXPR statement

Purpose | Scan a string for a matching "wildcard" or regular expression.
Syntax | REGEXPR mask$ IN target$ [AT start&] TO iPos& [, iLen&]

Remarks

REGEXPR scans target$ for a matching expression specified in mask$. If found, it returns the position of the match in the iPos& variable (indexed to the first character position), and optionally, the length of the matching expression in iLen&.

If a match is made, the iPos& and iLen& results can be immediately used with subsequent string operations such as MID$ to extract the matched portion of target$, and/or to continue the search through the remainder of target$. If no matching expression is found, both iPos& (and iLen& if specified) are set to zero.

If specified, the search begins at the character position target& in target$; however, start& must be between 1 and the length of target$. If start& is less than 1, the start& parameter is ignored.

While it is possible for more than one match to be found in a particular target string, REGEXPR first selects one or more matches which start at the leftmost possible position, then returns the longest of those. Use the \s special escape operator to force a match on the shortest match (see below).

The ^ and $ operators match on both the actual string start/end, or the previous/next embedded line-delimiter characters ( CHR$(13,10) or $CRLF) in target$. This enables REGEXPR to treat the target$ string as containing a set of "logical lines" of text. In this situation, the start& character position plays a crucial role in identifying which logical delimited line that should be examined by REGEXPR.

By default, search expressions are assumed to be case-insensitive, so capitalization is ignored.

mask$

The regular (wildcard) expression specified in mask$ may contain a combination of standard text characters and/or the metacharacters which are defined as follows:

Char | Definition
. | (period) Matches any character, except the end-of-line.
^ | (caret) Matches the actual beginning-of-line position or the preceding line-delimiter character pair (CHR$(13,10) or $CRLF), as taken from the start& character position. The line-delimiter characters themselves are not included in the iLen& result. (also see [^] below for usage within a character class definition).
$ | (dollar) Matches the end-of-line position, which may be either the first line-delimiter character pair (CHR$(13,10) or $CRLF) that is encountered in the search to the right of the start& position, or the actual end of the target$ string, whichever occurs first. The line-delimiter characters themselves are not included in the iLen& result.
| | (stile) Specifies alternation (the OR operator), so that an expression on either side can match. Precedence is from left-to-right, as encountered in the expression.
? | (question mark) Specifies that zero or one match of the preceding sub-pattern is allowed. Cannot be used with a Tag.
+ | (plus) Specifies that one or more matches of the preceding sub-pattern are allowed. Cannot be used with a Tag.
* | (asterisk) Specifies that zero or more matches of the preceding sub-pattern are allowed. Cannot be used with a Tag.
Character classes
[ ] | (square brackets) Identifies a user-defined class of characters, any of which will match: [abc] will match a, b, or c. Only three special metacharacters are recognized within a class definition, the caret ^ for complemented characters, the hyphen - for a range of characters, or one of the following \ backslash escape sequences:
| \\ \- \] \e \f \n \q \r \t \v \x##
| Any other use of a backslash within a class definition yields an undefined operation that should be avoided.
[-] | (hyphen) The hyphen identifies a range of characters to match. For example, [a-f] will match a, b, c, d, e, or f.
| Characters in an individual range must occur in the natural order as they appear in the character set. For example, [f-a] will match nothing.
| Lists of characters, and one or more ranges of characters, may be intermixed in a single class definition. The start and end of a range may be specified by a literal character, or one of the \ backslash escape sequences:
| \\ \- \] \e \f \n \q \r \t \v \x##
| Any other use of a backslash within a class definition yields an undefined operation.
| Multiple ranges in a class are valid. For example, [a-d2-5] matches a, b, c, d, 2, 3, 4, or 5.
| When the hyphen is escaped, it is treated as a literal. For example, [a\-c] is a list, not a range, and matches a, -, or c due to the \ backslash escape sequence.
[^] | (caret) When the caret appears as the first item in a class definition, it identifies a complemented class of characters, which will not match. For example, [^abc] matches any character except a, b, or c.
| A range can also be specified for the complemented class. For example, [^a-z] matches any character except a through z.
| A caret located in any position other than the first is treated as a literal character.
Tags/sub-patterns
( ) | (parentheses) Parentheses are used to match a Tag, or sub-pattern, within the full search pattern, and remember the match. The matched sub-pattern can be retrieved later in the mask (or in a replace operation with REGREPL), with \01 through \99, based upon the left-to-right position of the opening parentheses.
| Parentheses may also be used to force precedence of evaluation with the alternation operator. For example, "(Begin)|(End)File" would match either "BeginFile" or "EndFile", but without the Tag designations, "Begin|EndFile" would only match either "BeginndFile" or "BegiEndFile".
Escaped characters
\ | (backslash). The escape operator (single-character quote). The following character will be treated as a literal value rather than being interpreted as a special character. Note that the character following the backslash must actually be a special character, as follows:
\b | A word boundary. The start or end of a word, where a word is defined as one or more characters that include an alphabetic character (A-Z or a-z), a numeric character (0-9), and an underscore. For example, "abc_123" is considered a single word and "abc-123" is considered two words.
\c | Case-sensitive search. Without the \c operator, the default is to ignore case when matching. Unlike some other implementations of regular expressions, case-insensitivity is recognized in all operations, even a range of characters such as "[6-Z]". The \c operator may appear at any position in the mask.
\e | Escape character: CHR$(27) or $ESC.
\f | Formfeed character: CHR$(12) or $FF.
\n | Linefeed (or new-line) character: CHR$(10) or $LF.
\q | Double-quote mark ("): CHR$(34) or $DQ. \q is included for ease of inclusion within a literal string. For example: "\qHello\q".
\r | Carriage-return character: CHR$(13) or $CR.
\s | Shortest match character: The \s flag causes the shortest matching string to be returned, rather than the longest (the default). For example, when searching for the mask "abc.*abc" in "abcdabcabc", the default setting would return position 1 and length 10. With the \s switch set, it returns position 1 and length 7. This option may cause a slight increase in processing time. The \s flag must appear at the beginning of the mask string.
\t | Horizontal tab character: CHR$(9) or $TAB.
\v | Vertical tab character: CHR$(11) or $VT.
\x## | Hex character code: Indicates that an ASCII code follows, given by two hexadecimal digits. For example, \xFF = CHR$(&HFF) (which is equivalent to CHR$(255)). XX must be in the range 0 through 255.

Restrictions | To maximize performance, avoid overuse of the *, + and ? metacharacters.
See also | REGREPL, Online Regular Expression Tester

Example

a$ = "please send email to support@powerbasic.com"

b$ = "([a-z0-9._/+-]+)(@[a-z0-9.-]+)"

REGEXPR b$ IN a$ TO position&, length&

email_address$ = MID$(a$, position&, length&)

a$ = "Amount owed: $42.75 and is overdue!"

b$ = "\$[0-9.,]+"

REGEXPR b$ IN a$ TO position&, length&

amount$ = MID$(a$, position&, length&)

a$ = "Open 24 Hours"

b$ = "[^a-z ]+"

REGEXPR b$ IN a$ TO position&, length&

hours$ = MID$(a$, position&, length&)

a$ = "Line 1" + $CRLF + "Line 2" + $CRLF

b$ = "([0-9])$"

RESET position& : RESET length&

DO

position& = position& + length&

REGEXPR b$ IN a$ AT position& TO _

position&, length&

c$ = "Match at " + STR$(position&)

LOOP WHILE position&