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creadline

Why does readline() echo stdin to stdout?

I've written a small C program that uses readline("") to read input from stdin. Rather than interacting with it from the terminal, I've written a test harness which executes the C program and gives it input:

test harness --stdout--> | --stdin--> C program
         ^------stdin--- | <--stdout-----/

This test harness is receiving an echo of its output, even though the program itself. Why is readline() echoing its input, and can I disable this? Or should I not be using readline() in a non-interactive environment?

Solution

  • The readline library is solely intended for interactive use. Your program should probably fall back to using fgets() if isatty(STDIN_FILENO) is false.