Find Lines Lacking Closing Braces

Question

Is there an easy way to do this? Ideally, a closing bracket would be added to the line lacking the bracket. Is there a SED/AWK answer?

Some lines will read:

\url{http://google.com}

While others:

\url{http://google.com

I'd like to add a closing brace to those lines that contain an opening brace but lack a closing brace.

%%%%% The source file:

%\usepackage[anythingbreaks]{breakurl}
%\PassOptionsToPackage{hyphens}{url}\usepackage{hyperref}

%\usepackage[hyphens]{url}

\usepackage{url}
\urlstyle{rm}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\makeatother


\title{}
\author{}
\date{2019-08-19}
%\sloppy
\begin{document}

Answer 1

You can write a parse in Lua using LPEG which matches balanced braces. Be aware that this is line-based, i.e. if you have constructs where the braces span several lines, this will fail.

test.lua

local lpeg = require("lpeg")
local P, S, V = lpeg.P, lpeg.S, lpeg.V

local function err(match, pos, cap)
    print(match, pos, cap)
end

local rule = P{"text",
    any = 1 - S"{}",
    balanced = "{" * (V"any" + V"balanced")^0 * "}",
    text = V"any" * (V"balanced" + V"any")^0 * P(-1)
}

local path = arg[1] or error("Usage: " .. arg[0] .. " <filename>")
local file = io.open(path, "r")

local n = 1
for line in file:lines() do
    local match = rule:match(line)
    if not match then
        error("Closing } missing on line " .. n)
    end
    n = n + 1
end

test.tex

\documentclass{article}
\usepackage{url}
\begin{document}
\url{http://google.com
\end{document}

Running this with texlua gives

$ texlua test.lua test.tex
test.lua:21: Closing } missing on line 4

---

It is also possible to automatically add a closing brace on the offending line. To this end, we parse the line and if it fails, we add braces at the end until it succeeds.

test2.lua

local lpeg = require("lpeg")
local P, S, V = lpeg.P, lpeg.S, lpeg.V

local function err(match, pos, cap)
    print(match, pos, cap)
end

local rule = P{"text",
    any = 1 - S"{}",
    balanced = "{" * (V"any" + V"balanced")^0 * "}",
    text = V"any" * (V"balanced" + V"any")^0 * P(-1)
}

local path = arg[1] or error("Usage: " .. arg[0] .. " <filename>")
local file = io.open(path, "r")

for line in file:lines() do
    local match
    while not match do
        match = rule:match(line)
        if not match then
            line = line .. "}"
        end
    end
    print(line)
end

There are some obvious limitations with this approach, namely that the machine cannot know where exactly the closing brace has to be placed.

test2.tex

\documentclass{article}
\usepackage{url}
\begin{document}
Use \url{http://google.com to reach Google search
\end{document}

Running against the example above gives syntactically correct but semantically wrong output:

$ texlua test2.lua test2.tex
\documentclass{article}
\usepackage{url}
\begin{document}
Use \url{http://google.com to reach Google search}
\end{document}

This is not fixable using an automated approach. Only the user can know where the closing brace has to be placed to be semantically correct.

Answer 2

I commissioned several programs to fix the issue. Two are Java programs. One is a Javascript program. The other is a python script. Here is a link: https://www12.zippyshare.com/v/9f8cIYpY/file.html

The Javascript and python programs worked for me. Your luck with the Java files depends on the nature of the file you're trying to fix. My file sometimes had two URL's on the same line and this caused the Java programs to gag.

This may have been the reason the lua script proposed by @henrimenke didn't work for me.