Why does bash return the file directory when using a back tick?

Question

I'm running this series of commands

passwd=`wc -l /etc/passwd`

echo $passwd

Returns:

34 /etc/passwd

What do I need to do to this so that it will only show the output of wc -l?

Answer 1

Just read from standard input instead of giving wc a file name:

$ passwd=`wc -l < /etc/passwd`
$ echo "$passwd"
      86

wc still outputs quite a bit of padding, but the file name is omitted (because wc has no idea what file the data comes from).

Answer 2

That's the default behaviour of wc:

» wc -l /etc/passwd                                     
28 /etc/passwd

There is no way to tell wc not to output the filename.

Answer 3

Using awk perhaps ?

$ passwd=$(wc -l /etc/passwd | awk '{print $1}')
$ echo $passwd
32

Using cut, from cut (GNU coreutils)

$ passwd=$(wc -l /etc/passwd | cut -d" " -f1)
$ echo $passwd
32

Answer 4

wc returns also the filename, but there are other ways to do it. Some examples:

passwd=`wc -l /etc/passwd | grep -o [1-9]\*`

or

passwd=`wc -l /etc/passwd | cut -f1 -d' '`

(answer from this question: get just the integer from wc in bash)