How to use the command 'exrex' (with examples)

Exrex is a powerful command-line tool used to generate all or random matching strings for a given regular expression. It can also simplify regular expressions and has some fun features like printing eyes or a boat. This command-line utility is particularly helpful for software developers and testers who need to see potential matches for regex patterns, validate regex behavior, or create test data.

Use case 1: Generate all possible strings that match a regular expression

Code:

exrex 'regular_expression'

Motivation:
Generating all possible strings that match a regex pattern is useful for testing and validation purposes. It allows developers to understand how their regex will behave across all possible matching conditions and ensure it captures the intended matches without errors or omissions.

Explanation:
In this command, exrex is followed by a regular expression string as its sole argument. The tool reads this regex and outputs every possible string that could satisfy the pattern.

Example Output:
If the regular expression is exrex '[ab]{2}', the output would be:

aa
ab
ba
bb

Use case 2: Generate a random string that matches a regular expression

Code:

exrex --random 'regular_expression'

Motivation:
Generating a random string that matches a regex can be useful for generating test data or for applications that require random inputs matching specific patterns, like passwords or unique identifiers.

Explanation:
The --random flag signals exrex to output only one random match instead of all possible matches. This is useful when you need just one example for testing or sampling.

Example Output:
For the regex exrex --random '[ab]{2}', a possible output could be:

ba

Use case 3: Generate at most 100 strings that match a regular expression

Code:

exrex --max-number 100 'regular_expression'

Motivation:
Sometimes the set of possible strings is very large or infinite. Limiting the output to a manageable number, such as 100, allows developers to review a representative sample of matches without overwhelming their system or themselves.

Explanation:
The --max-number 100 argument tells exrex to limit the output to a maximum of 100 strings that match the given regular expression.

Example Output:
For exrex --max-number 100 '[01]{4}', some possible outputs include:

0000
0001
0010
...

Use case 4: Generate all possible strings that match a regular expression, joined by a custom delimiter string

Code:

exrex --delimiter ", " 'regular_expression'

Motivation:
Generating strings with a custom delimiter can be particularly helpful for creating human-readable lists or feeding into other systems that require input in a specific format.

Explanation:
The --delimiter ", " argument joins all generated strings with the specified delimiter before outputting them. This can be useful for quick and easy integration and presentation of the generated data.

Example Output:
Running exrex --delimiter ", " '[ab]{2}' might yield:

aa, ab, ba, bb

Use case 5: Print count of all possible strings that match a regular expression

Code:

exrex --count 'regular_expression'

Motivation:
Sometimes, it is important to know the size of the set of all possible matches to a regex. This is crucial when evaluating performance implications or determining the comprehensiveness of test coverage.

Explanation:
The --count flag tells exrex to output the number of possible strings that match the given expression, without actually enumerating them.

Example Output:
For exrex --count '[a-c]{2}', the output might be:

9

Use case 6: Simplify a regular expression

Code:

exrex --simplify 'ab|ac'

Motivation:
Simplifying a regex can make it more readable and maintainable. This is especially helpful when working with complex patterns that might have redundant or overlapping components.

Explanation:
The --simplify flag tells exrex to optimize the regular expression by eliminating redundancies or unnecessary complexity.

Example Output:
For the expression exrex --simplify 'ab|ac', the simplified output will remain the same as the original due to its optimal form:

ab|ac

Use case 7: Print eyes

Code:

exrex '[oO0](_)[oO0]'

Motivation:
This use case is an amusing feature illustrating the novelty of exrex, showcasing its ability to create fun, regex-based ASCII designs or patterns.

Explanation:
The regular expression [oO0](_)[oO0] generates patterns resembling eyes, using various characters to assemble eye-like outputs.

Example Output:
Possible outputs might include:

o_o
O_O
O_0
...

Use case 8: Print a boat

Code:

exrex '( {20}(\| *\\|-{22}|\|)|\.={50}| ( ){0,5}\\\.| {12}~{39})'

Motivation:
Similar to the previous use case, this demonstrates a creative application of regex—generating ASCII art. It’s an interesting way to engage with regular expressions beyond their standard text processing capabilities.

Explanation:
This lengthy regex is designed to create an ASCII art representation of a boat. Each part of the regex contributes different components of the illustration, using characters, spacing, and repetition.

Example Output:
The output resembles an ASCII-art boat:

                      \                                       
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                               

Conclusion:

Exrex is a versatile tool, providing extensive functionality for visualization, simplification, and creative applications of regular expressions. Whether you’re a developer testing regex patterns, generating test data, or just having fun with ASCII art, exrex offers a range of options to enhance your command-line toolkit.