argdo in Vim

Load files with

:args *.txt

Then do things via

:bufdo 1d
:bufdo 1

to delete line 1 from each file and then write. Note argdo will open each file in the arg list, and do the command. Whereas bufdo will do the command on each open buffer, and tabdo will do the command on each open tab.

Note that this particular task is better done with sed via

sed -i -e '1d' *.txt