You can do that as a one-liner (I have kept the unused “re” module import, to keep it as close to your code as possible): python -c 'import re, sys; print("\

You can do that as a one-liner (I have kept the unused “re” module import, to keep it as close to your code as possible): python -c 'import re, sys; print("\n".join(str(line.lower().count("foo")) for line in sys.stdin))' or if you want to avoid building one large output string: python -c 'import re, sys; print(*(line.lower().count("foo") for line in sys.stdin), sep="\n")' if memory consumption is still an issue: python -c 'import re, sys; set(print(line.lower().count("foo")) for line in sys.stdin)' (This creates a useless Set object and throws it away as a side effect.)