built in - How to use the read command in Bash?

Question

When I try to use the read command in Bash like this:

echo hello | read str
echo $str

Nothing echoed, while I think str should contain the string hello. Can anybody please help me understand this behavior?

Answer 1

The read in your script command is fine. However, you execute it in the pipeline, which means it is in a subshell, therefore, the variables it reads to are not visible in the parent shell. You can either

• move the rest of the script in the subshell, too:

  echo hello | { read str
    echo $str
  }
  

• or use command substitution to get the value of the variable out of the subshell

  str=$(echo hello)
  echo $str
  

  or a slightly more complicated example (Grabbing the 2nd element of ls)

  str=$(ls | { read a; read a; echo $a; })
  echo $str