While-loop over lines from variable in bash

Assume a file file with multiple lines.

$ cat file
foo
bar
baz

Assume further that I wish to loop through each line with a while-loop.

$ while IFS= read -r line; do
$   echo $line
$   # do stuff
$ done < file
foo
bar
baz

Finally, please assume that I wish to pass lines stored in a variable rather than lines stored in a file. How can I loop through lines that are saved as a variable without receiving the below error?

$ MY_VAR=$(cat file)
$ while IFS= read -r line; do
$   echo $line
$   # do stuff
$ done < $(echo "$MY_VAR")
bash: $(echo "$MY_VAR"): ambiguous redirect

Solution

You have several options:

A herestring (note that this is a non-POSIX extension): done <<<"$MY_VAR"
A heredoc (POSIX-compliant, will work with /bin/sh):
```
done <<EOF
$MY_VAR
EOF
```
A process substitution (also a non-POSIX extension, but using printf rather than echo makes it more predictable across shells that support it; see the APPLICATION USAGE note in the POSIX spec for echo): done < <(printf '%s\n' "$MY_VAR")

Note that the first two options will (in bash) create a temporary file on disk with the variable's contents, whereas the last one uses a FIFO.