The Open Source Zone

Redet allows the user to construct regular expressions and test them against input data by executing any of a variety of search programs, editors, and programming languages that make use of regular expressions. When a suitable regular expression has been constructed it may be saved to a file. redet stands for Regular Expression Development and Execution Tool. For each program, a palette showing the available regular expression syntax is provided. Selections from the palette may be copied to the regular expression window with a mouse click. Users may add their own definitions to the palette via their initialization file. Redet also keeps a list of the regular expressions executed, from which entries may be copied back into the regular expression under construction. The history list is saved to a file and restored on startup, so it persists across sessions. So long as the underlying program supports Unicode, redet allows UTF-8 Unicode in both test data and regular expressions.

Redet is but one of a number of tools that provide assistance in using regular expressions with different capabilities and purposes. Which one should you choose?

Here are some of Redet's distinctive properties:

• Redet supports many programs. Most other regexp tools are aimed at a single language or style of regular expression.
• Redet determines the properties of the programs that actually execute the regular expressions empirically. This guarantees that the version of the program you are using will actually behave as described. It also makes it likely that if new features are added to a program's regular expression repertoire, they will be detected and shown on the palette without any modification to the program.
• Redet is explicitly designed for use in a variety of languages and writing systems. It provides the ability to change locale without exiting and reports whether Unicode support is available for each combination of program and locale. It provides special support for Unicode, such as lists of Unicode ranges and character properties. Redet itself is fully internationalized. By adding a suitable translation catalogue, buttons, labels, and messages may all be provided in any language.
• Most regular expression tools are useful for constructing and understanding regular expressions but are not designed for use as search environments. Redet provides a number of facilities that make it a good search environment, including a relatively large, re-sizable text window, the ability to enter both regular expressions and data in various ways and to save them to files, editable, persistent history, and journalling.
• Redet handles both matching and substitution. Most programs deal only with matching.
• Redet allows the user to define named character classes and to intersect them.

Even I don't think that Redet is the best tool for all purposes. For one thing, it assumes that the user knows something about regular expressions or is willing to spend some time learning. The novice who doesn't want to learn more or doesn't have time to should try txt2regex which walks the user through the construction of the regular expression and generates output for 20 different programs and languages. It is one of the few tools that isn't specialized for a particular language or program.

Some programs provide details about the matching process. regex-coach, for example, can single-step through the match and show the parse tree, so it is useful if you want to understand the matching process in detail. It uses PERL-style regular expressions. Regexpviewer will show you which portions of the text were matched by which group in the regular expression. It uses Tcl regular expressions. Kiki and Kodos are similar, rather more elaborate, tools for Python. Programs like Redet that support many different regular expression matchers cannot provide this kind of detail because they don't execute the regular expressions themselves.

Some programs provide insight into the relationship between regular expressions and finite state automata and into the implementation of regular expression engines. re_graph draws the finite state automaton corresponding to a given regular expression. qfsm is a graphical tool for designing finite state automata directly.