Regular Expressions Interview Questions And Answers

• In complex search
• In validation like email validation or URl validation etc
• in writing of rewrite rules in apache or .htaccess file
• in file search in linux
• in pattern matches

• "^PCDS": Symbols ^ use to matches any string that starts with "PCDS"
  this can match "PCDS is an Infotech";
• "pcds$": Matches a string that ends in the substring "pcds"
  like "This is pcds";
• "^pcds$": Matches a string that starts and ends with "pcds"
  that could only be "pcds" itself
• "ab*": matches a string that has an a followed by zero or more b's ("a", "ab", "abbb", etc.);
• "ab+": same as *, but there's at least one b ("ab", "abbb", etc.);
• "ab?": there might be a b or not;
• "ab.": . matches any character like abd, abh, abt etc;
• "ab{2}": matches a string that has an a followed
  by exactly two b's ("abb");
• "ab{2,}": there are at least two b's ("abb", "abbbb", etc.);
• "ab{3,5}": from three to five b's ("abbb", "abbbb", or "abbbbb").
• "[a-z]": matches any char from a to z.

In order to be taken literally, you must escape the characters "^.[$()|*+?{\" with a backslash ('\'), as they have special meaning. On top of that, you must escape the backslash character itself in PHP3 strings, so, for instance, the regular expression "(\$|¥)[0-9]+" would have the function call: ereg("(\\$|¥)[0-9]+", $str)