The Dired command ! (dired-do-shell-command) reads a shell command string in the minibuffer and runs that shell command on all the specified files. X is a synonym for !. You can specify the files to operate on in the usual ways for Dired commands (Section 30.7). There are two ways of applying a shell command to multiple files:
If you use * in the shell command, then it runs just once, with the list of file names substituted for the *. The order of file names is the order of appearance in the Dired buffer.
Thus, ! tar cf foo.tar * RET runs tar on the entire list of file names, putting them into one tar file foo.tar.
If the command string doesn't contain *, then it runs once for each file, with the file name added at the end.
For example, ! uudecode RET runs uudecode on each file.
What if you want to run the shell command once for each file, with the file name inserted in the middle? You can use ? in the command instead of *. The current file name is substituted for ?. You can use ? more than once. For instance, here is how to uuencode each file, making the output file name by appending .uu to the input file name:
uuencode ? ? > ?.uu
To use the file names in a more complicated fashion, you can use a shell loop. For example, this shell command is another way to uuencode each file:
for file in *; do uuencode $file $file >$file.uu; done
The working directory for the shell command is the top-level directory of the Dired buffer.
The ! command does not attempt to update the Dired buffer to show new or modified files, because it doesn't really understand shell commands, and does not know what files the shell command changed. Use the g command to update the Dired buffer (Section 30.14).