Control output of c++ program using makefile

Question

I have an executable called print-word-length.cc that takes prints the length of words using from a *.txt file.

So in my makefile, ./print-word-length </dir/dictionary.txt prints out words in the dictionary.

How would I go about just printing the first 10 lengths of words in dictionary.txt?

I've tried head -n 10 ./print-word-length </dir/dictionary.txt, but it prints gibberish.

question from:https://stackoverflow.com/questions/66054672/control-output-of-c-program-using-makefile

Answer 1

This isn't a makefile question, it's a shell scripting question. You solve the problem by writing a shell command at your shell prompt, then you just put that same solution into your makefile.

The head utility prints the first lines it reads from standard input or from a file. It doesn't run a command that you give it as an argument.

It's printing the first 10 lines of the contents of your program file, which is binary "gibberish" as you say.

This is what pipes are for:

./print-word-length.cc </dir/dictionary.txt | head -n10

This says: start print-word-length.cc and set it up so whatever it prints to its output is sent to the head command as its input.