Regular expression to parse a double number

Here is the simple example of how to validate your input is really a double value. But first here is a king of WRONG regexp: \d+.\d+ and variants of this example. Whats wrong with this expression. Well, it

- DOES NOT match the sign (positive or negative)
- Requires obligatary dot character
- Requires obigatory digits after dot

Now here is the PROPER expression: ^[\+\-]{0,1}([ 0-9]+\.){0,1}[ 0-9]+$

- You may or may not set the sign before a number
- You may parse values like these: 100, 100.0, 0.11, +1, -3000, -1.2
- This expression makes you sure the string contains at least one digit

However such the expression does not support parsing the values like 1.23e-10 etc, but it can e simply extended to support such ones.

Useful regular expression: how to verify perforce branch path

Here is the regular expression (aka regexp) pattern to verify if the input string matches the rules of perforce branch specification (the string should look like this: //depot/level1/level2/level3/... )

//(?:\w+?/)+?(?:\.\.\.$)

 Symbols ?:  mean that we would not like to capture them (does not make sense for match function of regular expression but still reasonable to make the logic of the pattern clear)/