diff --git a/2018/day1/day1.py b/2018/day1/day1.py
index 9e05675..6404f56 100644
--- a/2018/day1/day1.py
+++ b/2018/day1/day1.py
@@ -17,6 +17,8 @@ def main(inp):
 
     
 if __name__ == '__main__':
-    with open("input.txt") as inp:
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as inp:
         main(inp.readlines())
 
diff --git a/2019/day1/day1.py b/2019/day1/day1.py
index 55009a3..057a266 100644
--- a/2019/day1/day1.py
+++ b/2019/day1/day1.py
@@ -32,10 +32,13 @@ def test_part2():
 
 
 if __name__ == "__main__":
-    print("Part 1 - total mass: ", calculate_total_fuel_mass("./input.txt"))
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+
+    print("Part 1 - total mass: ", calculate_total_fuel_mass(infile))
 
     test_part2()
     print(
         "Part 2 -- total mass: ",
-        calculate_total_fuel_mass("./input.txt", calculate_fuel_iterative),
+        calculate_total_fuel_mass(infile, calculate_fuel_iterative),
     )
diff --git a/2019/day2/day2.py b/2019/day2/day2.py
index 7913f2e..1725bc3 100644
--- a/2019/day2/day2.py
+++ b/2019/day2/day2.py
@@ -54,7 +54,9 @@ def run_program(memory, noun, verb):
 
 if __name__ == "__main__":
     tests()
-    with open("input.txt") as inp:
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as inp:
         memory = [int(x) for x in inp.readline().strip().split(",")]
         # Pass a copy to avoid modifying the original memory
         print("Part 1 answer: ", run_program(memory[:], 12, 2))
diff --git a/2019/day3/day3.py b/2019/day3/day3.py
index 7188378..7729105 100644
--- a/2019/day3/day3.py
+++ b/2019/day3/day3.py
@@ -70,8 +70,9 @@ def tests():
 
 if __name__ == "__main__":
     tests()
-
-    with open("input.txt") as raw_input:
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as raw_input:
         lines = raw_input.readlines()
         wire1, wire2 = [line.strip("\n").split(",") for line in lines]
         print("Part 1 -- distance = ", find_min_distance(wire1, wire2))
diff --git a/2021/day1/day1.py b/2021/day1/day1.py
index adef306..0fd2fa1 100644
--- a/2021/day1/day1.py
+++ b/2021/day1/day1.py
@@ -40,5 +40,7 @@ def part2(infile):
 
 
 if __name__ == "__main__":
-    part1("./input.txt")
-    part2("./input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    part1(infile)
+    part2(infile)
diff --git a/2021/day2/day2.py b/2021/day2/day2.py
index 64021a6..89a8850 100644
--- a/2021/day2/day2.py
+++ b/2021/day2/day2.py
@@ -39,4 +39,6 @@ def main(input_file):
 
 
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)
diff --git a/2021/day3/day3.py b/2021/day3/day3.py
index 7b7d0ff..e17162a 100644
--- a/2021/day3/day3.py
+++ b/2021/day3/day3.py
@@ -64,4 +64,6 @@ def main(input_file):
 
 
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)
diff --git a/2021/day4/day4.py b/2021/day4/day4.py
index 98ece64..d657a80 100644
--- a/2021/day4/day4.py
+++ b/2021/day4/day4.py
@@ -94,4 +94,6 @@ def main(input_file):
 
 
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)
diff --git a/2021/day5/day5.py b/2021/day5/day5.py
index 3128904..dcc6313 100644
--- a/2021/day5/day5.py
+++ b/2021/day5/day5.py
@@ -35,7 +35,7 @@ def main(infile):
     print(res)
 
 
-
-
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)
diff --git a/2021/day6/day6.py b/2021/day6/day6.py
index bac503d..c2106f6 100644
--- a/2021/day6/day6.py
+++ b/2021/day6/day6.py
@@ -23,4 +23,6 @@ def main(infile):
     print(f"Part 2, {res}")
 
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)
diff --git a/2021/day6/day6_2.py b/2021/day6/day6_2.py
index d7f5908..565baf2 100644
--- a/2021/day6/day6_2.py
+++ b/2021/day6/day6_2.py
@@ -31,4 +31,4 @@ def rotate(l):
 for j in range(256):
     numbers = rotate(numbers)
     numbers[6] += numbers[8]
-    print(f'DAY {j+1} AMOUNT OF FISH: {sum(numbers)}')
\ No newline at end of file
+    print(f'DAY {j+1} AMOUNT OF FISH: {sum(numbers)}')
diff --git a/2021/day7/day7.py b/2021/day7/day7.py
index d7f487a..d6a2ee0 100644
--- a/2021/day7/day7.py
+++ b/2021/day7/day7.py
@@ -26,8 +26,10 @@ def part2(crabs):
 
 
 if __name__ == "__main__":
-    with open("input.txt") as infile:
-        crabs = [int(x) for x in infile.readline().split(",")]
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as f:
+        crabs = [int(x) for x in f.readline().split(",")]
     part1(crabs)
     part2(crabs)
 
diff --git a/2021/day8/day8.py b/2021/day8/day8.py
index 62d76fb..2fc3930 100644
--- a/2021/day8/day8.py
+++ b/2021/day8/day8.py
@@ -43,4 +43,6 @@ def main(infile):
 
 
 if __name__ == "__main__":
-    main("input.txt")
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    main(infile)