I am looking for a terminal way. Open all files in
/foo/bar containing the string
You didn't say how you want to open them :)
One way is to use grep to recursively look for the string in your files (-r). Use -l to ask grep to output only the filenames of matching files. This will output one filename per line, use xargs to build a suitable command line for your editor.
this also works with gedit; just change vim for gedit.
You can also use find for this but it's more complicated IMHO:
Opens files containing