Home / server / Questions / 97112
Accepted
Noah Campbell
Asked: 2009-12-24 16:56:14 +0800 CST

Using a select inside a while read is NOT giving me the result I want

  • 772

I have a file "in" that contains:

a
b
c

I run the following command:

cat in | while read el; do select yn in "yes" "no"; do echo $yn; done; done;

And get the following output:

1) yes
2) no
#?
#? 
#?

What I want is to be able to type 1 or 2 at each iteration. What do I need to do differently to make this work?

bash

2 Answers

  1. Best Answer

    You're piping input into a while loop. Within the loop, stdin comes from the preceding command, not from the console. Your select statement is reading from the same pipe that the read statement is reading from.

    Also, you don't need cat.

    You need to preserve stdin for use in the select statement. Try this:

    while read el; do select yn in "yes" "no"; do echo $yn; break; 
done <&4; done 4<&0 < in

    First, note that we're redirecting input using '<', rather than using cat.

    This preserves your origin stdin (fd 0) in fd 4, and then inside the loop redirects input to select from fd 4.

    • 1

  2. select will read an input and execute it repeatedly until EOF; what you almost certainly want is the superficially similar:

    cat in | while read el; do select yn in "yes" "no"; do echo $yn; break; done; done
    • 0