You can test everything out here:
I would like to extract the value of individual variables paying attention to the different ways they have been defined. For example, for dtime we want to extract 0.004. It also has to be able to interpret exponential numbers, like for example for variable vis it should extract 10e-6.
The problem is that each variable has its own number of white spaces between the variable name and the equal sign (i dont have control on how they have been coded)
Text to test:
dtime = 0.004D0
case = 0
newrun = 1
periodic = 0
iscalar = 1
ieddy = 1
mg_level = 5
nstep = 20000
vis = 10e-6
ak = 10e-6
g = 9.81D0
To extract dtime's value this REGEX works:
(?<=dtime =\s)[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?
To extract dtime's value this REGEX works:
(?<=vis =\s)[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?
The problem is that I need to know the exact number of spaces between the variable name and the equal sign. I tried using \s+ but it does not work, why?
(?<=dtime\s+=\s)[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?
If you are using PHP or PERL or more generally PCRE then you can use the \K flag to solve this problem like this:
dtime\s+=\s\K[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?
^^
Notice the \K, it tells the expression to ignore everything
behind it as if it was never matched
Edit: I think you need to capture the number in a capturing group if you can't use look behinds or eliminate what was matched so:
dtime\s*=\s*([-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?)