Constructing a regular expression to match particular strings can be
a long and painful task. This regex tool aims to help the
development of the proper regular expressions by providing a quick way
to test your regular expression against an arbitrary string. The
regex tool uses POSIX regular expressions, not Perl
regular expressions. Details on using regex are found
below.
The source for the regex tool is contained within the
regex.c; instructions for building the tool can be found
here.
The most current version of regex can be found at:
http://www.castaglia.org/proftpd/contrib/regex.c
Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this tool.
regex, simply do:
gcc -o regex regex.c
http://www.castaglia.org/proftpd/doc/contrib/regexp.htmlThe
regex tool can be used while reading the introduction to
try out the regular expression features it describes.
Some of the information displayed may not be helpful for you; the
regex tool was written to aid in the development of the
mod_rewrite module for proftpd, hence why it
delves deeper into the specifics of regular expression matching than the
average system administrator may need.
Running regex without any parameters, or with the wrong number
of parameters, reminds you of that it needs parameters for doing its job:
# ./regex regex: missing required parameters:A simple test:# ./regex foo regex: missing required parameters:
# ./regex foo bar regex: compiled pattern 'bar' (1 group) regex: pattern 'bar' did NOT match string 'foo'Be aware, however, that your shell may not handle some characters as you would assume:
# ./regex $foo bar regex: missing required parameters:In this case, the shell assumed that $foo was a variable, and it tried to replace $foo with its value (apparently an empty string). Similarly:
# ./regex $foo$ bar regex: compiled pattern 'bar' (1 expression) regex: pattern 'bar' did NOT match string '$'When this happens, you may have to surround your string and/or pattern with quotes, in order to prevent your shell from handling these special characters:
# ./regex '$foo$' bar regex: compiled pattern 'bar' (1 expression) regex: pattern 'bar' did NOT match string '$foo$' # ./regex '$foo$' '$bar$' regex: compiled pattern '$bar$' (1 expression) regex: pattern '$bar$' did NOT match string '$foo$'The "compiled pattern" line reports on the pattern that is being compiled as the regular expression; this is how you can tell whether the shell is transforming your pattern into something different before passing it to the
regex tool.
In many of these examples, you see "(1 expression)" or "(2 expressions)" displayed; what are these?
#./regex 39065 '[0123456789]+(\.|,)[0-9]+$' regex: compiled pattern '[0123456789]+(\.|,)[0-9]+$' (2 expressions) regex: pattern '[0123456789]+(\.|,)[0-9]+$' did NOT match string '39065'The number of expressions in a given pattern increases if you use alternations (i.e. the
| vertical bar character).
Sometimes the regex tool will display a "substring"
line, like so:
# ./regex 39065 '[0-9]+$' regex: compiled pattern '[0-9]+$' (1 expression) regex: substring[0]: '39065' [0-5] regex: pattern '[0-9]+$' matched string '39065'This shows that the first substring (starting at zero) is
39065,
that the substring starts at offset 0, and ends at offset
5.
These examples are from a case where a user needs a particular
proftpd Filter expression for some filesystem
paths; the strength of regex lies in the ability to test out
such filters without running the program itself:
# ./regex //incoming/39065 '[0123456789]+(\.|,)[0-9]+$' regex: compiled pattern '[0123456789]+(\.|,)[0-9]+$' (2 expressions) regex: pattern '[0123456789]+(\.|,)[0-9]+$' did NOT match string '//incoming/39065' # ./regex //incoming/39065 '^[0-9]+$' regex: compiled pattern '^[0-9]+$' (1 expression) regex: pattern '^[0-9]+$' did NOT match string '//incoming/39065' # ./regex //incoming/39065 '[0-9]+$' regex: compiled pattern '[0-9]+$' (1 expression) regex: substring[0]: '39065' [11-16] regex: pattern '[0-9]+$' matched string '//incoming/39065'