Files and folders

Your desktop is a mess: photos from three trips mixed together, a “final_FINAL_v2.docx”, and a hundred screenshots. With a mouse you’d drag files one by one into new folders.

In the shell you do it with a few short commands: make a folder, move everything that matches into it, rename what’s badly named, delete what you don’t need. And once you know the commands, you can do it for a thousand files as easily as for three.

One warning, in a friendly way: rm deletes immediately. There’s no Recycle Bin, no “are you sure?”. That’s why programmers pause for a moment before pressing Enter on an rm. (In this pretend computer, you can always press Start over.)

The real words

mkdir, touch, cp, mv, rm:

• Wildcards match many names at once: *.jpg means “every name ending in .jpg”. mv *.jpg photos/ moves them all.
• Permissions: ls -l shows something like -rwxr-xr--:
  • The first character: - for a file, d for a folder.
  • Then three groups of three: the owner, the group, and everyone else.
  • r = read, w = write (change), x = execute (run it as a program, or enter it if it’s a folder). A - means “not allowed.”
  • chmod +x script.sh makes a file runnable (lesson 4).
• Names with spaces need quotes: mv "my file.txt" myfile.txt. Many programmers avoid spaces in file names for this reason.