# Rexpy

## The `rexpy` command

```
rexpy [FLAGS] [inputfile [outputfile]]
```

If `inputfile` is provided, it should contain one string per line;
otherwise lines will be read from standard input.

If `outputfile` is provided, regular expressions found will be written
to that (one per line); otherwise they will be written to standard output.

Optional `FLAGS` may be used to modify Rexpy's behaviour:

* `-h`, `--header`  
  Discard first line, as a header.

* `-?`, `--help`  
  Print this usage information and exit (without error).

* `-g`, `--group`  
  Generate capture groups for each variable fragment
  of each regular expression generated, i.e. surround
  variable components with parentheses, e.g.

      `^[A-Z]+\-[0-9]+$`

  becomes

      `^([A-Z]+)\-([0-9]+)$`

* `-q`, `--quote`  
  Display the resulting regular expressions as
  double-quoted, escaped strings, in a form broadly
  suitable for use in Unix shells, JSON, and string
  literals in many programming languages. e.g.

      `^[A-Z]+\-[0-9]+$`

  becomes

      `"^[A-Z]+\\-[0-9]+$"`

* `--portable`  
  Produce maximally portable regular expressions
  (e.g. `[0-9]` rather than `\d`). (This is the default.)

* `--grep`  
  Same as `--portable`

* `--java`  
  Produce Java-style regular expressions (e.g. `\p{Digit}`)

* `--posix`  
  Produce POSIX-compliant regular expressions
  (e.g. `[[:digit:]]` rather than `\d`).

* `--perl`  
  Produce Perl-style regular expressions (e.g. `\d`)

* `-u`, `--underscore`, `-_`  
  Allow underscore to be treated as a letter.
  Mostly useful for matching identifiers.

* `-d`, `--dot`, `-.`, `--period`  
  Allow dot to be treated as a letter.
  Mostly useful for matching identifiers.

* `-m`, `--minus`, `--hyphen`, `--dash`  
  Allow minus to be treated as a letter.
  Mostly useful for matching identifiers.

* `-v`, `--version`  
  Print the version number.

* `-V`, `--verbose`  
  Set verbosity level to 1

* `-VV`, `--Verbose`  
  Set verbosity level to 2

* `-vlf`, `--variable`  
  Use variable length fragments

* `-flf`, `--fixed`  
  Use fixed length fragments


## Rexpy Examples

```{eval-rst}
.. automodule:: tdda.rexpy.examples
    :members:
```