bash line concatenation during variable interpolation

Question

$ cat isbndb.sample | wc -l
13
$ var=$(cat isbndb.sample); echo $var | wc -l
1

Why is the newline character missing when I assign the string to the variable? How can I keep the newline character from being converted into a space?

I am using bash.

Answer 1

You have to quote the variable to preserve the newlines.

$ var=$(cat isbndb.sample); echo "$var" | wc -l

And cat is unnecessary in both cases:

$ wc -l < isbndb.sample
$ var=$(< isbndb.sample); echo "$var" | wc -l

Edit:

Bash normally strips extra trailing newlines from a file when it assigns its contents to a variable. You have to resort to some tricks to preserve them. Try this:

IFS='' read -d '' var < isbndb.sample; echo "$var" | wc -l

Setting IFS to null prevents the file from being split on the newlines and setting the delimiter for read to null makes it accept the file until the end of file.

Answer 2

var=($(< file))
echo ${#var[@]}