$? возвращает errorlevel 0 вместо 4

Python 3.x решение:

diff_marked.py скрипт:

import sys

file1_name = sys.argv[1]
file2_name = sys.argv[2]

with open(file1_name, 'r') as f1, open(file2_name, 'r') as f2:
    f1_lines = f1.readlines()  # list of lines of File1
    f2_lines = f2.readlines()  # list of lines of File2

    for k,l in enumerate(f1_lines):
        f1_fields = l.strip().split('|')  # splitting a line into fields by separator '|'
        if k < len(f2_lines) and f2_lines[k]:
            has_diff = False
            f2_fields = f2_lines[k].strip().split('|')
            for i,f in enumerate(f1_fields):
                if f != f2_fields[i]:    # comparing respective lines 'field-by-field' between two files
                    f1_fields[i] = '**' + f + '**'  # wrapping differing fields
                    f2_fields[i] = '**' + f2_fields[i] + '**'
                    has_diff = True

        if has_diff:
            print(f1.name)  # print file name
            print('|'.join(f1_fields))
            print(f2.name)
            print('|'.join(f2_fields))

Использование: (у вас может быть другая версия Python, текущий случай был протестирован на python 3.5)

python3.5 diff_marked.py File1 File2 > diff_output

diff_output content:

File1
1|piyush|bangalore|**dev**
File2
1|piyush|bangalore|**QA**
File1
3|rohit|**delhi**|**QA**
File2
3|rohit|**bangalore**|**dev**