So how does one use the modifiers ismx etc if there is no trailing /? The solution is to use extended regular expressions , i.e. /abc/i becomes (?i)abc. See also Placement of modifiers below. The pattern matching behaves in various slightly different ways, depending on the setting of the multi-line and single-line modifiers. Note that the single-line and multi-line operators have nothing to do with each other; they can be specified independently. Single-line mode Single-line mode only affects how the '.' meta-character is interpreted. Default behaviour is that '^' and '$' only match at the very beginning and end of the string. When Multi-line mode is used, the '^' metacharacter matches at the beginning of every line, and the '$' metacharacter matches at the end of every line. Regular expressions use certain characters as meta characters - these characters have a special meaning to the RE engine. Such characters must be escaped by preceeding them with \ (backslash) in order to treat them as ordinary characters. Here is a list of the meta characters and their meaning (please check the ORO documentation if in doubt). Modifiers can be placed anywhere in the regex, and apply from that point onwards. [A bug in ORO means that they cannot be used at the very end of the regex. However they would have no effect there anyway.] Another approach is to use a simple test plan to test the regular expressions. The Java Request sampler can be used to generate a sample, or the HTTP Sampler can be used to load a file. Add a Debug Sampler and a Tree View Listener and changes to the regular expression can be tested quickly, without needing to access any external servers.