-- lua grep.lua [-hvcnli] PATTERN [FILE...]
-- lua grep.lua [-hvcnli] -e PATTERN [FILE...]
-- prints lines from FILEs which match PATTERN
-- if no FILEs are given, stdin is used

function toupper(ch)
    if (string.byte(ch) >= string.byte("a"))
        and (string.byte(ch) <= string.byte("z")) then
        return string.char(string.byte(ch) + string.byte("A")
                           - string.byte("a"))
    else
        return ch
    end
end

function grepmatch(options, pattern, line)
    local result
    if options.i then
        pattern = string.gsub(pattern,"%l",toupper)
        line = string.gsub(line,"%l",toupper)
    end
    result = (string.find(line, pattern) ~= nil)
    if options.v then result = not result end
    return result
end

function grep(options, pattern, filehandle, filename)
    local lineno = 0
    local matchcount = 0
    local out
    for line in filehandle:lines() do
        lineno = lineno + 1
        if grepmatch(options, pattern, line) then
            if options.l then
                print(filename)
                break
            elseif options.c then
                matchcount = matchcount + 1
            else
                out = line
                if options.n then
                    out = tostring(lineno) .. ":" .. out
                end
                if options.printnames then
                    out = filename .. ":" .. out
                end
                print(out)
            end
            matched = true
        end
    end
    if options.c then
        out = tostring(matchcount)
        if options.printnames then
            out = filename .. ":" .. out
        end
        print(out)
    end
end

require "getopt"

options = getopt(arg, "hvcne:li")
argn = arg.n
scriptname = arg[0]
pattern = options.e or arg[1]
files = arg
table.remove(files, 0) -- remove program name
table.remove(files, 0) -- remove pattern
nfiles = argn - 1
options.printnames = (nfiles > 1) and (not options.h)

matched = false
if nfiles == 0 then
    grep(options, pattern, io.input(), "<stdin>")
else
    for i = 0, nfiles-1 do
        fh = io.open(files[i])
        if fh == nil then
            print("error opening " .. files[i])
        else
            grep(options, pattern, fh, files[i])
            fh:close()
        end
    end
end
if matched then
    os.exit(0)
else
    os.exit(1)
end