Two different ways for reading from stdin

Question

Hard to google this one, I have this:

echo "age" |  while read line; do
    echo "$line"
done

but there there is this style:

while read line; do
    echo "$line"
done < echo "age"

first, the second style is not quite right, but is there a name for the first and second styles? is there any functional/behavioral difference?

`< echo "age"` will try to read the input from a file named `echo`. `<` is a file redirection. What you want is `< <(echo "age")` or `<<< "age"` " — Barmar, May 09 '19 at 19:12
`<(echo "age")` is **process substitution**, `<<< "age"` is a **here-string**. — Barmar, May 09 '19 at 19:13
But you probably want the heredoc: `while read line; do ...; done << EOF` — William Pursell, May 09 '19 at 20:19

score 1 · Answer 1 · answered May 09 '19 at 20:22

The biggest functional difference is that the first (in bash) will run the loop in a subshell. As a result, $line will lose its value after the loop is done. To avoid the subshell, you can embed the content directly in the shell with a heredoc:

while read line; do
    echo "$line"
done << EOF
age
EOF

Two different ways for reading from stdin

1 Answers1