#!/usr/bin/env lua51
--[[
  gsub.lua - answer the lines from stdin that match a certain
  pattern, transforming them in a certain way.
  Usage:
         gsub.lua    <pat1> <pat2> 
         gsub.lua -f <pat1> <pat2_expr> 

  Author:  Eduardo Ochs
  Version: 2006jul07
  Public Domain.

#
# Example 1:
# (find-fline "~/o")
cat /var/lib/dpkg/info/manpages-dev.list \
  | gsub.lua '/usr/share/man/man3/(.+)%.3%.gz' '# (find-man "3 %1")' \
  | sort | tee ~/o

#
# Example 2, using "-f":
# http://www.freedb.org/freedb/rock/cf0d740f
# (find-angg ".zshrc" "cddb2rentracks")
gsub.lua -f \
  'TTITLE([0-9]+)=(.*)' \
  'function (n, name) return
       format("renwav %02d %s", n+1, string.lower(gsub(name, "[ \039]", "_")))
     end' \
  < $S/http/www.freedb.org/freedb/rock/cf0d740f

#
  See also:
  (find-blogmefile "blogme.lua" "eval =")
  (find-angg "LUA/lua50init.lua" "compat")
  table.remove
--]]

if arg[1] == "-f" then p2isfunction = true; tremove(arg, 1) end

-- Hack: '' as the first argument becomes '^(.*)$' - "use the whole line"
if arg[1] == "" then arg[1] = "^(.*)$" end

p1 = arg[1]
p2 = arg[2]

eval = function (body) return assert(loadstring(body))() end
expr = function (body) return assert(loadstring("return "..body))() end
if p2isfunction then
  p2 = expr(p2)
end

for li in io.lines() do
  local newli, n = string.gsub(li, p1, p2)
  if n > 0 then
    print(newli)
  end
end