Script that outputs the total number of lines in all the text files that are passed as arguments

You can accomplish your goal simply by using cat and a pipeline:

cat "$@" | wc -l 

If you really wanted to sum manually, you can do this with awk:

for f in "$@"; do wc -l < "$f" done | awk '{ sum+=$1 } END { print sum }' 

Or if you really wanted to parse the last line of wc, removing the string "total":

wc -l "$@" | awk 'END { print $1 }' 

Building on jordanm’s answer:

1. Pipe all the data through a single instance of wc -l

 if [ "$#" -gt 0 ] then cat -- "$@" | wc -l else echo 0 fi 

or
 

 cat -- /dev/null "$@" | wc -l 

• Use -- "$@" to guard against filenames beginning with -.
• Avoid invoking cat with no arguments, as that will cause it to read the standard input.
• Note that cat a_single_file | something is the classic form of the dreaded Useless Use of Cat, but cat one_or_more_file(s) | something can be OK (although it’s still not ideal).

2. Rely on the fact that wc issues a “total” line

 if [ "$#" -gt 0 ] then wc -l -- /dev/null "$@" | tail -1 else echo 0 total fi 

or
 

 wc -l -- /dev/null /dev/null "$@" | tail -1 

• Note that wc issues a total line only if it has at least two filename arguments.

3. Use awk without using wc

 if [ "$#" -gt 0 ] then awk 'END {print NR}' -- "$@" else echo 0 fi 

or
 

 awk 'END {print NR}' -- /dev/null "$@" 

Warning:

The above commands will not all produce the same answer if any of the files end with a character other than newline.

sed -ne\$= files... 

Just hand sed as many filenames as you want in place of files... and, when it has read all of them, it will report the =line-number of the very $last in its input.