splitt

#!/usr/bin/env lua
--[[

awk fail to extract columns from more than one file. 
This little script provide a simple solution to extract 
a column from each file. Field separator is space or any other 
non alphanumeric character. It uses the lua %w format, but 
a bit more complex: "[%d%a%.]+" line 76.

splitt file1 columnX .. fileN columnZ

Written when stranded overnight at Arlanda Airport from Umeå to Oslo
by Ole W. Saastad, 20 May 2016.

Last update 7. Nov 2024.

]]

-- Process arguments, how many files to process.
if #arg==0 then
    print("usage: splitt file1 columnX .. fileN columnZ")
    os.exit(1)
end
if not (#arg%2==0) then
    print("Number of arguments must even")
    print("usage: splitt file1 columnX  file2 columnY file3 columnZ ....")
    os.exit(1)
end
files=#arg/2

-- Some arrays to store each column's values
local f={} -- files, an array of file pointers.
local c={} -- column numbers, just a simple numeric array.
local i = 0

-- Read the arguments 
for j = 1, files*2, 2 do
   i = i + 1
   f[i]=io.open(arg[j],"r")   -- keep file pointers in an array.
   if f[i]==nil then      
      print("usage: splitt file1 columnX .. fileN columnZ")
      print("usage: failed to open file:",arg[j])
      os.exit(1)
   end
end
i = 0
for j = 2, files*2, 2 do
   i = i + 1
   c[i]=tonumber(arg[j])
   if not c[i] then
     print("usage: splitt file1 columnX .. fileN columnZ")
     print("Expected number got :",arg[j])
     os.exit(1)
  end
end

-- some extra variables to do process the data
local col={}
local line={} 
local pos = 0
local word = 0
local eol = false
local eof = false

for i = 1, files, 1 do
   line[i] = f[i]:read()
end

while not eof do -- While still more lines to read from the files.

   for i = 1, files, 1 do -- loop through all the files given 
      eol = false -- No end of line 
      word = 0
      pos = 0

      while not eol do -- parse the line in the i'th file.
         local s, e = string.find(line[i], "[%d%a%.]+", pos) -- %w alphanumeric chars
         if s then -- found a word?
            pos = e + 1    -- next position is after this word
            word = word + 1 
            if word == c[i] then
               col[i]=string.sub(line[i], s, e) -- extract the word.
               eol= true -- no need to read any more after we found the col.
            end
         else -- if s, false no more words.
            print()
            print("Column ",c[i]," not found in file",arg[i*2-1])
            print("Giving up")
            os.exit(1)
         end -- if s
      end -- while not eol
      io.write(string.format("%s ",col[i])) -- print out the column value.      
   end -- for i = 1, files, 1
   print()

   for i = 1, files, 1 do  
      line[i] = f[i]:read()  -- Read the next line from the files.
   end
   
   for i = 1, files, 1 do
      if line[i]==nil then eof = true end -- End of file ?
   end

end -- while not eof, if no more to read we're done.