If you would like to use vim in a manner similar to sed, you may use the -c flag to run an ex command from the command line. This command will run automatically before presenting the file to you. For example, to replace foo with bar:

vim file.txt -c "s/foo/bar"

This will open up the file with all instances of foo replaced with bar. If you would to like to make changes to the file without having to manually save, you can run multiple ex commands, and have the last command write and quit. For example:

vim file.txt -c "s/foo/bar" -c "wq"

Important note:

You can not run multiple ex commands separated by a bar |. For example

vim file.txt -c "s/foobar | wq"

Is not correct; however, it CAN be done if you use ex.

ex -c ":%s/this/that/g | wq" file.txt