How to fix mismatched brackets in a TeX string? - regex

Question

For example I have a lot of Tex strings like
|u(x,t)|^2 = \frac{1}{\sqrt{1+(4+t)^2))e^{-\frac{2(x-k_0t)^2}{1+4t^2))
The problem with the above Tex is that the bracket is not matching. \frac{1}{\sqrt{1+(4+t)^2)) should be \frac{1}{\sqrt{1+(4+t)^2}} and {-\frac{2(x-k_0t)^2}{1+4t^2)) should be {-\frac{2(x-k_0t)^2}{1+4t^2}}
wrong: \frac{1}{\sqrt{1+(4+t)^2))
right: \frac{1}{\sqrt{1+(4+t)^2}}
wrong: {-\frac{2(x-k_0t)^2}{1+4t^2))
right: {-\frac{2(x-k_0t)^2}{1+4t^2}}
explanation: The first example is not right, because for last two ) there is no ) matching it, and it should be } to match previous {
I want to know how to automatically correct such mismatched brackets? I have perl installed and I intended to do it with regex, but can't figure out a way.

Answer 1

I don't know if I'm understanding you correctly, but it sounds to me like you need to count brackets and make sure that the number of ( or [ or { is equal to the number of corresponding ) or ] or }.
One possible solution is using a hash for every line of TeX and storing values in it (not sure how the file looks. I assume all lines are like you provided):
#!/usr/bin/perl
use strict;
use warnings;
my $file = shift;
my $line_num = 0;
open FH, "<$file" or die "Error: $!\n";
while(<FH>) {
my %brackets = (
'(' => 0,
'[' => 0,
'{' => 0
);
$line_num++;
my #chars = split //, $_;
### Count brackets.
foreach my $char (#chars) {
if ($char eq '(' or $char eq '[' or $char eq '{') {
$brackets{$char}++;
} elsif ($char eq ')' or $char eq ']' or $char eq '}') {
if ($char eq ')') { $brackets{'('}--; }
if ($char eq ']') { $brackets{'['}--; }
if ($char eq '}') { $brackets{'{'}--; }
} else {
next;
}
}
### Check that all hash values are 0.
foreach my $bracket (keys %brackets) {
if ($brackets{$bracket} != 0) {
print "In line $line_num: '$bracket' missing $brackets{$bracket} closing brackets.\n";
}
}
}
This code will at least tell you where the errors occured and give you a general idea of the nature of these errors. for input such as )ff){gfs[[y[46rw] the output will be:
In line 1: '{' missing 1 closing brackets.
In line 1: '[' missing 2 closing brackets.
In line 1: '(' missing -2 closing brackets.
Instead of printing the brackets (or storing the number of brackets. Probably better to store index of the brackets) you can write simple code to fix this because at this point, you'll have all the information you need.
This is not a simple question if the errors in the file have no pattern. I recommend looking for one before actually trying

Answer 2

There must be some kind of condition, which indicates where the parenthesis are used instead of the braces. I assume that it is either in front of e^ and at the end of the line.
This fixes the first one:
perl -pi~ -e 's/\)\)e\^/}}e^/' file.tex
And this the second:
perl -pi~ -e 's/\)\)$/}}/' file.tex