local filename = ...; assert(filename); local infile = assert(io.open("infile", "r"))
local contents = infile:read("*all")
print(contents)
io.stdout:write("> ")
local command = io.stdin:read("*line")
local delimiter = string.sub(command, 1, 1)
local other_delimiter = string.find(command, delimiter, 2)
local pattern = string.sub(command, 2, other_delimiter - 1)
local substitute = string.sub(command, other_delimiter + 1)
contents = string.gsub(contents, pattern, substitute, 1)
local outfile = assert(io.open("outfile", "w"))
outfile:write(contents)
outfile:close()