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 

Answer 2

Other bash alternatives that do not involve a subshell:

read str <<END             # here-doc hello END  read str <<< "hello"       # here-string  read str < <(echo hello)   # process substitution