3. Deleting Files and Directories

Deleting files

  • We can pass the paths to non-existent files in an existing directory as arguments to create empty files with the command touch, which will make two empty files in the current directory:
machine_name:~/test_dir/test2$ touch a b
  • To remove a file, pass a path to that file to the program rm as an argument; try deleting the file a you just created from outside the directory it’s in like so:
machine_name:~/test_dir/test2$ cd ..
machine_name:~/test_dir$ rm test2/a
machine_name:~/test_dir$ ls test2

Deleting directories

  • To delete a directory and its contents (if any), have to pass the -r flag to the rm program:
machine_name:~/test_dir$ cd ..
machine_name:~$ rm -r test_dir

If you run rm test_dir without the -r flag, the shell will complain since test_dir is a directory, not a file.

Shell program flags

  • More generally, an option (often called a flag) is another way to change the behavior of a program besides an argument.

  • A shell program knows which argument is which from the order of them, while options have names (e.g. -r) that the program can recognize.

  • As another example of helpful flags, let’s return to the ls command that lists the contents of a directory

    • If you specify the -l flag when running ls, the shell will list the contents of the directory with much more detailed information, such as the size of the file and the last time it was modified.
    • If you also specify the -h flag, then the file sizes will be provided in “human-readable” form, i.e. in KB, MB, GB, or TB instead of in raw bytes (if you can do the conversions quickly in your head, good on you!)
    • Note that you can specify multiple flags after a -, e.g.
        machine_name:~$ ls -lh

My favorite flag combination is ls -ltrh to list files in a long format in reverse chronological order and human readable format. I used this combination so frequently, I aliased this command to be just l in my ~/.bash_profile.

More resources

We’ll only have time to scratch the surface of interacting with computers via the shell today. See lessons 1 and 3 of the Missing Semester open-source MIT course on miscellaneous software engineering skills for more in-depth information and tips about making the most of the shell.