\(
\newcommand{\P}[]{\unicode{xB6}}
\newcommand{\AA}[]{\unicode{x212B}}
\newcommand{\empty}[]{\emptyset}
\newcommand{\O}[]{\emptyset}
\newcommand{\Alpha}[]{Α}
\newcommand{\Beta}[]{Β}
\newcommand{\Epsilon}[]{Ε}
\newcommand{\Iota}[]{Ι}
\newcommand{\Kappa}[]{Κ}
\newcommand{\Rho}[]{Ρ}
\newcommand{\Tau}[]{Τ}
\newcommand{\Zeta}[]{Ζ}
\newcommand{\Mu}[]{\unicode{x039C}}
\newcommand{\Chi}[]{Χ}
\newcommand{\Eta}[]{\unicode{x0397}}
\newcommand{\Nu}[]{\unicode{x039D}}
\newcommand{\Omicron}[]{\unicode{x039F}}
\DeclareMathOperator{\sgn}{sgn}
\def\oiint{\mathop{\vcenter{\mathchoice{\huge\unicode{x222F}\,}{\unicode{x222F}}{\unicode{x222F}}{\unicode{x222F}}}\,}\nolimits}
\def\oiiint{\mathop{\vcenter{\mathchoice{\huge\unicode{x2230}\,}{\unicode{x2230}}{\unicode{x2230}}{\unicode{x2230}}}\,}\nolimits}
\)
Regular expressions are used for matching text.
You can test regular expressions online at [1].
Syntax
Letters
[a-zA-Z]
Numbers
You should match numbers using [0-9].
\d will match unicode characters which are classified as digits.
See \d vs 0-9
Useful Regular Expressions
Mostly copied from Regex DB.
Floating Point Number
Without matching scientific notation (e.g. 1.5e-6).
Reference
With matching scientific notation (e.g. 1.5e-6).
Reference
Capturing significand and exponent separately.
([-+]?[0-9]*\.?[0-9]+)(?:[eE]([-+]?[0-9]+))?
Capturing the entire string together.
([-+]?[0-9]*\.?[0-9]+(?:[eE][-+]?[0-9]+)?)
