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Regular expressions are used for complex string manipulation in PHP.A regular expression is a pattern that is matched against a subject string from left to right. To interpret data you need regular expressions. In PHP regular expessions are accessed through functions. ereg() ereg_replace() eregi() eregi_replace() split() spliti() sql_regcase() Meta Characters =============== Part of a pattern that is in square brackets is called a "character class". In a character class the only meta- characters are: \ general escape character ^ negate the class, but only if the first character - indicates character range ] terminates the character class Outside square brackets, the meta-characters are as follows: \ general escape character ^ start of line $ end of line . match any character except newline (by default) [ start character class definition ] end character class definition | start of alternative branch ( start subpattern ) end subpattern ? extends the meaning of (, also 0 or 1 quantifier, also quantifier minimizer * 0 or more quantifier + 1 or more quantifier { start min/max quantifier } end min/max quantifier It is always safe to precede a non-alphameric with "\". It can also be used with non printable chracters. Like ... /a alarm, /cchar control + char where char is the character /e escape,/f form feed, /n newline, /r carrige return /t tab Backslash can also be used for specifying generic charac- ter types: \d - any decimal digit \D - any character that is not decimal digit. \s - any whitespace character \S - any character that is not white space. \w - any word character \W - any non word character. Matching Strings ================ While matching strings two meta-character are widely used $(dollar sign) and ^ (circumflex) sign. $ sign tells PHP to match the string at the end of the string, the ^sign will match any pattren at the beginning of the string. Expression ^liquidpulse would match the following .. liquidpulse is one of the best web resource liquidpulse is best php resource Expression resource$ will also match the above lines. Matching Escape Sequences ========================= Consider expression jerrett\ntaylor. Criteria (jerret, linebreak,taylor) would match followings liquidpulse taylor is lastname of Jerrett Character Classes ================= [a-zA-z] Match any letter [a-zA-Z0-9] Match any letter or number [ \t\n\v\r\f] Match any whitespace character [0-9\.\-] Match any number, minus sign or period To negate the character class, you can use the ^ meta character but only when ^ is the very first character inside the brackets like [^a-z] More then one Occurance of a Character Usee {} metacharacter [A-Z]{5} Number 5 tells PHP to match a string that contains five uppercase characters in a row.To match a range of characters specify lower and upper limits like {1,6} The * quantifier will match zero or more occurrences of a character and the + quantiier will match one or more occurences of a character. [a-z]* will match zero or more occurences of lowercase letters in a string. Optional Matches ================ ? meta-character is used for this purpose [a-z]{4}? would optionally match four occurences of any lowercase characters so following would be valid. NETRPX jerrett taylor LP Predefined character Classes ============================ [[:alnum:]] All alphanumeric characters [a-zA-Z09] [[:alpha:]] All alphabatic characters [a-Z] [[:blank:]] Tab and Space [[:cntrl:]] All the control characters [[:digit:]] All decimal digits [0-9] [[:graph:]] All printable characters except space [[:lower:]] All lowecase characters [[:print:]] All printable characters [[:punct:]] Punctuation marks [\.,;:-] [[:space:]] All whitespace characters [[:upper:]] All the upercase letters [A-Z] [[:xdigit:]] The set of hexadecimal digits To negate the class make sure that you put ^ inside the first bracket. [^[:digit:]] The pipe (|) Delimiter Here is an example (liquidpulse|netrpx) , PHP will match either liquidpulse or netrpx. | ||||||||||
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