string.find using directory path in Lua

Question

Hello,

I need to translate this piece of code from Perl to Lua

open(FILE, '/proc/meminfo');   
while(<FILE>)  
{  
    if (m/MemTotal/)  
    {  
        $mem = $_;  
        $mem =~ s/.*:(.*)/$1/;
    }  
    elseif (m/MemFree/)
    {
        $memfree = $_;
        $memfree =~ s/.*:(.*)/$1/;
    }
}
close(FILE);

So far I've written this

while assert(io.open("/proc/meminfo", "r")) do
    Currentline = string.find(/proc/meminfo, "m/MemTotal")
    if Currentline = m/MemTotal then
        Mem = Currentline
        Mem = string.gsub(Mem, ".*", "(.*)", 1)
    elseif m/MemFree then
        Memfree = Currentline
        Memfree = string.gsub(Memfree, ".*", "(.*)", 1)
    end
end
io.close("/proc/meminfo")

Now, when I try to compile, I get the following error about the second line of my code

luac: Perl to Lua:122: unexpected symbol near '/'

obviously the syntax of using a directory path in string.find is not like how I've written it. 'But how is it?' is my question.

Answer 1

To iterate a file line by line you can use io.lines.

for line in io.lines("/proc/meminfo") do
    if line:find("MemTotal") then --// Syntactic sugar for string.find(line, "MemTotal")
        --// If logic here...
    elseif --// I don't quite understand this part in your code.
    end
end

No need to close the file afterwards.

Answer 2

You don't have to stick to Perl's control flow. Lua has a very nice "gmatch" function which allows you to iterate over all possible matches in a string. Here's a function which parses /proc/meminfo and returns it as a table:

function get_meminfo(fn)
    local r={}
    local f=assert(io.open(fn,"r"))
    -- read the whole file into s
    local s=f:read("*a")
    -- now enumerate all occurances of "SomeName: SomeValue"
    -- and assign the text of SomeName and SomeValue to k and v
    for k,v in string.gmatch(s,"(%w+): *(%d+)") do
            -- Save into table:
        r[k]=v
    end 
    f:close()
    return r
end
-- use it
m=get_meminfo("/proc/meminfo")
print(m.MemTotal, m.MemFree)