subtitle-glue.py

from pysubs2 import *
import sys


def main(argv=sys.argv):
    if len(argv) <= 2:
        print("Usage: python subtitle-glue.py output-file input-files")
        return

    subs = SSAFile()
    for i in range(2, len(argv)):
        try:
            new_subs = load(argv[i])
            for ev in new_subs:
                subs.append(ev)
        except Exception as e:
            print("Input file exception: " + str(e) + " (" + argv[i] + ")")
            return
    subs.sort()

    output = argv[1]
    try:
        subs.save(output)
    except Exception as e:
        print("Output file exception: " + str(e) + " (" + output + ")")
        return

    print("Subtitles saved successfully at " + output)


if __name__ == "__main__":
    main()

Usage:

1. Install http://pythonhosted.org/pysubs2/. Just use pip: pip install pysubs2. You can also clone the pysubs2 GitHub repository and install via python setup.py install.
2. Download this file
3. Run in terminal python subtitle-glue.py output-file input-files. Count of input files may be from 1 to infinity.
   Example: python subtitle-glue.py result.ass first-part.srt second-part.srt
   Supported formats are SRT, ASS, SUB.