Loop over environment variables in POSIX sh

Question

I need to loop over environment variables and get their names and values in POSIX sh (not bash). This is what I have so far.

#!/usr/bin/env sh

# Loop over each line from the env command
while read -r line; do
  # Get the string before = (the var name)
  name="${line%=*}"
  eval value="\$$name"

  echo "name: ${name}, value: ${value}"
done <<EOF
$(env)
EOF

It works most of the time, except when an environment variable contains a newline. I need it to work in that case.

I am aware of the -0 flag for env that separates variables with nul instead of newlines, but if I use that flag, how do I loop over each variable? Edit: @chepner pointed out that POSIX env doesn't support -0, so that's out.

Any solution that uses portable linux utilities is good as long as it works in POSIX sh.

Answer 1

There is no way to parse the output of env with complete confidence; consider this output:

bar=3
baz=9

I can produce that with two different environments:

$ env -i "bar=3" "baz=9"
bar=3
baz=9
$ env -i "bar=3
> baz=9"
bar=3
baz=9

Is that two environment variables, bar and baz, with simple numeric values, or is it one variable bar with the value $'3\nbaz=9' (to use bash's ANSI quoting style)?

---

You can safely access the environment with POSIX awk, however, using the ENVIRON array. For example:

awk 'END { for (name in ENVIRON) {
            print "Name is "name;
            print "Value is "ENVIRON[name];
           }
         }' < /dev/null

With this command, you can distinguish between the two environments mentioned above.

$ env -i "bar=3" "baz=9" awk 'END { for (name in ENVIRON) { print "Name is "name; print "Value is "ENVIRON[name]; }}' < /dev/null
Name is baz
Value is 9
Name is bar
Value is 3
$ env -i "bar=3
> baz=9" awk 'END { for (name in ENVIRON) { print "Name is "name; print "Value is "ENVIRON[name]; }}' < /dev/null
Name is bar
Value is 3
baz=9