Question

I have a file, foo.txt, containing the following lines:

a
b
c

I want a simple command that results in the contents of foo.txt being:

a
b

Answer 1

Using GNU sed:

sed -i '$ d' foo.txt

The -i option does not exist in GNU sed versions older than 3.95, so you have to use it as a filter with a temporary file:

cp foo.txt foo.txt.tmp
sed '$ d' foo.txt.tmp > foo.txt
rm -f foo.txt.tmp

Of course, in that case you could also use head -n -1 instead of sed.

MacOS:

On Mac OS X (as of 10.7.4), the equivalent of the sed -i command above is

sed -i '' -e '$ d' foo.txt