file does not update with affect of `sed` deletion

Question

I am having trouble with getting a file updated with the effect of a sed deletion.

when i perform the following, replacing <> with appropriate filename

sed '$d' <filename>

the immediate shell output shows the last line was deleted, but upon doing

cat <filename>

it shows that this deletion hasn't been stored, why is this?

Answer 1

You need the -i flag to change the file in place. Without it, sed writes to standard output.