Replace $ x <y $ with $ x <y $

Question

I want to search the text for a smaller sign <between dollar signs, for example $x<y$, and replace it with $x < y$.

I use mathjax and less than a character, causes some problems when rendering Mathjax. (See here: http://docs.mathjax.org/en/latest/tex.html#tex-and-latex-in-html-documents ).

I tried $text = preg_replace("/\$(.*?)(<)(.*?)\$/","/\$$1 < $3\$/",$text), but I'm not sure if this is a good solution. I am new to programming :)

Thank you for your help.

Answer 1

It's too complicated to take regex seriously, I think ...

< $, (. n-dru).

:

$output = preg_replace(<<<'REGEX'
(\$\K\s*((?:[^<$\s]+|(?!\s+[<$])\s+)*)\s*(?=(?:<(*ACCEPT)|\$|$)(*SKIP)(*F))
# \$\K => avoid the leading $ in the match
# ((?:[^<$\s]+|(?!\s+[<$])\s+)*) => up to $ or <, excluding surrounding spaces
# (?=(?:<(*ACCEPT)|\$|$)(*SKIP)(*F)) => accept matches with <, reject these without
|(?!^)<\K\s*((?:[^<$\s]+|(?!\s+[<$])\s+)*)\s*(\$|)
# (?!^) => to ensure we are inside $ ... $
# <\K => avoid the leading < in the match
|[^$]+(*SKIP)(*F)
# skip everything outside $ ... $
)x
REGEX
, " $1$2 $3", $your_input);

: https://regex101.com/r/fP9aG5/2

, $x<y<z$ = > $x < y < z$ ( $ x < y < z $), . preg_replace_callback:

$output = preg_replace_callback(<<<'REGEX'
(\$\K\s*((?:[^<$\s]+|(?!\s+[<$])\s+)*)\s*(?=(?:<(*ACCEPT)|\$|$)(*SKIP)(*F))
|(?!^)<\K\s*((?:[^<$\s]+|(?!\s+[<$])\s+)*)\s*(\$|)
|[^$]+(*SKIP)(*F))x
REGEX
, function($m) {
    if ($m[1] != "") return "$m[1] ";
    if ($m[3] != "") return " $m[2]$m[3]";
    return " $m[2] ";
}, $your_input);

$your_input :

random < test
nope $ foo $ bar < a $ qux < biz $fx<hk$
$foo<bar<baz$ foo  buh < bar < baz $
$ foo $ a < z $ a < b < z $

preg_replace_callback, , :

random < test
nope $ foo $ bar < a $qux < biz$fx<hk$
$foo<bar<baz$foo  buh < bar < baz$
$ foo $ a < z $a < b < z$

Answer 2

- :

$text = preg_replace('/\$([^$< ]+)<([^$< ]+)\$/','$$1 < $2$', $text);

DEMO

Answer 3

. , .

$text = preg_replace("/\\$(.{1,20})<(.{1,20})\\$/", "\$$1 < $2\$", $text);

In this expression, you have {1,20} that you can use as a parameter, as max long (in this case 20) can be your variable on the left and right.