问题
I have a some HTML text in mathjax format:
text = "an inline \\( f(x) = \frac{a}{b} \\) equation, a display equation \\[ F = m a \\] \n and another inline \\(y = x\\)"
(Note: equations are delimited by single slashes, e.g. \(, not \\(, the extra \ is just escaping the first one for ruby text).
I want to get the output that substitutes this into, say an image created by latex.codecogs, e.g.
desired_output = "an inline <img src="http://latex.codecogs.com/png.latex?f(x) = \frac{a}{b}\inline"/> equation, a display equation <img src="http://latex.codecogs.com/png.latex?F = m a"/> \n and another inline <img src="http://latex.codecogs.com/png.latex?y = x\inline"/> "
Using Ruby. I try:
desired = text.gsub("(\\[)(.*?)(\\])", "<img src=\"http://latex.codecogs.com/png.latex?\2\" />")
desired = desired.gsub("(\\()(.*?)(\\))", "<img src=\"http://latex.codecogs.com/png.latex?\2\\inline\")
desired
But this is unsuccessful, returning only the original input. What did I miss? How do I construct this query appropriately?
回答1:
Try:
desired = text.gsub(/\\\[\s*(.*?)\s*\\\]/, "<img src=\"http://latex.codecogs.com/png.latex?\\1\"/>")
desired = desired.gsub(/\\\(\s*(.*?)\s*\\\)/, "<img src=\"http://latex.codecogs.com/png.latex?\\1\inline\"/>")
desired
The important changes that had to happen:
- The first parameter for
gsubshould be a regex (as Anthony mentioned) - If the second parameter is a double-quoted string, then the back references have to be like
\\2(instead of just\2) (see the rdoc) - The first parameter was not escaping the
\
There were a couple of other minor formatting things (spaces, etc).
回答2:
Not sure if your regexp is right - but in Ruby, Regexp are delimited by //, try like this :
desired = text.gsub(/(\\[)(.*?)(\\])/, "<img src=\"http://latex.codecogs.com/png.latex?\2\" />")
You were trying to do string substition, and of course gsub wasn't finding a string containing (\\[)(.*?)(\\])
来源：https://stackoverflow.com/questions/13166112/ruby-regexp-to-replace-equations