# 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]+)$

  This is now the default.

* `-G`, `--no-group`  
  Do not generated 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)=

## Supplied Rexpy Examples

TDDA rexpy is supplied with a set of examples.

To copy the rexpy examples, run the command:

```
tdda examples rexpy
```

This will create or overwrite a directory `rexpy_examples`
in the current directory.

Alternatively, you can copy all examples using the following command:

```
tdda examples
```

which will create a number of separate subdirectories.

```{include} ../../tdda/rexpy/examples/README.md
:heading-offset: 1
:start-line: 2
```