Bash – Why does this “while read” work in a terminal, but not in a shell script

It's because the part where you use the vars is a new set of commands. Use this instead:

head somefile | { read A B C D E FOO; echo $A $B $C $D $E $FOO; }

Note that, in this syntax, there must be a space after the { and a ; (semicolon) before the }.  Also -n1 is not necessary; read only reads the first line.

For better understanding, this may help you; it does the same as above:

read A B C D E FOO < <(head somefile); echo $A $B $C $D $E $FOO

Edit:

It's often said that the next two statements do the same:

head somefile | read A B C D E FOO
read A B C D E FOO < <(head somefile)

Well, not exactly. The first one is a pipe from head to bash's read builtin. One process's stdout to another process's stdin.

The second statement is redirection and process substitution. It is handled by bash itself. It creates a FIFO (named pipe, <(...)) that head's output is connected to, and redirects (<) it to the read process.

So far these seem equivalent. But when working with variables it can matter. In the first one the variables are not set after executing. In the second one they are available in the current environment.

Every shell has another behavior in this situation. See that link for which they are. In bash you can work around that behavior with command grouping {}, process substitution (< <()) or Here strings (<<<).

In your link, the variable used outside (linecount) is not defined as a "loop" variable. It's just modified (incremented) inside the body loop, but not in the "while" statement.

This is because when the "read -r f1 f2..." part is called, it reset (prepare) the variables used (f1 ..f7), wait for an input line and assign the variables according to the input. At the end of the file, it does not get any input line (EOF or Pipe Error), returns false, and exits the loop. But it already has reset the variables.

You can figure it for yourself by enabling the "debug mode" by adding set -x before your while statement.

This will produce something like :

++ IFS=:
++ read -r f1 f2 f3 f4 f5 f6 f7
++ echo 'Username: bind. Home directory:/var/cache/bind'
Username: bind. Home directory:/var/cache/bind
++ IFS=:
++ read -r f1 f2 f3 f4 f5 f6 f7
++ echo

You can see the last read being called, then your final "echo $f1".

So, as stated in your link, create another storage variable before your while, assign it the value and then you'll be able to use it :

typeset f0=""
while IFS=: read -r f1 f2 f3 f4 f5 f6 f7; do
  echo "Username: $f1. Home directory:$f6"
  f0="$f1"
done</etc/passwd
echo $f0