mergeLines.py

#!/usr/bin/env python

'''
Merge/Join/Combine lines of multiple input files.
Write lines consisting of the sequentially corresponding lines from each input file, separated by space character, to output file.
TODO: implements params like https://github.com/coreutils/coreutils/blob/master/src/paste.c
'''

import sys
from contextlib import ExitStack
from itertools import zip_longest


def main(args):
  if len(args) < 3:
    print(sys.argv[0] + ' <input-file-1> <input-file-2> [<input-file-n>...] <output-file>')
    sys.exit(0)
  mergeFiles(args[:len(args)-1], args[len(args)-1])


def mergeFiles(inputFileNames, outputFileName, delimiterChar=" ", fillValue="-"):
  with ExitStack() as eStack:
    inputFiles = [eStack.enter_context(open(fileName, 'r', encoding='utf-8', errors='replace')) for fileName in inputFileNames]    
    with open(outputFileName, 'w', encoding='utf-8', errors='replace') as outputFile:    
      for tupleOfLineFiles in zip_longest(*inputFiles, fillvalue=fillValue):
        outputFile.write(delimiterChar.join(map(str.strip, tupleOfLineFiles)) + "\n")

if __name__ == "__main__":
  main(sys.argv[1:])