In bash, how do I count the number of lines in a variable?

I have a variable which has a string stored in it and need to check if it has lines in it:

var=`ls "$sdir" | grep "$input"`

pseudo-code:

while [ ! $var's number of lines -eq 1 ]
  do something

That's my idea on how to check it. echo $var | wc -l doesn't work - it always says 1, even though it has 3.

echo -e doesn't work as well.

Quotes matter.

echo "$var" | wc -l

The accepted answer and other answers posted here do not work in case of an empty variable (undefined or empty string).

This works:

echo -n "$VARIABLE" | grep -c '^'

For example:

ZERO=
ONE="just one line"
TWO="first
> second"

echo -n "$ZERO" | grep -c '^'
0
echo -n "$ONE" | grep -c '^'
1
echo -n "$TWO" | grep -c '^'
2