The command line

Files live in a tree of folders, and a path names a place in it. pwd says where you are, ls lists what is here and cd moves you, with full paths from the top (/), short paths from where you are, .. for the folder above and ~ for home.

1. Where will you be?
2. Try: find your way
3. Worked example: reading a path › Three ways to name one folder
4. Worked example: reading a path › Find the mistake
5. Worked example: reading a path › Which command?
6. Vary: other ways to move › A full path
7. Vary: other ways to move › Up with ..
8. Vary: other ways to move › Home
9. Practise: paths › Full paths
10. Practise: paths › The prompt
11. Practise: paths › Review: the OS
12. Find and read a file

cat prints a whole file and grep prints only the lines that contain a word. Names that start with a dot are hidden: ls skips them, ls -a shows them. With these you can find anything on a computer you can't see.

1. What ls shows
2. Try: find the hidden file
3. Worked example: grep › grep cat pets.txt, line by line
4. Worked example: grep › Find the mistake
5. Worked example: grep › Capital letters
6. Vary: find it fast › One line
7. Vary: find it fast › Count
8. Vary: find it fast › Read from here
9. Practise: reading › A huge log
10. Practise: reading › Hidden
11. Practise: reading › Review: paths
12. The treasure hunt, part 1

mkdir makes a folder, cp copies, mv moves or renames, rm deletes and echo … > saves text into a file. rm is for good: there is no recycle bin in a shell, so look before you delete.

1. After rm
2. Try: back it up, then delete
3. Worked example: cp or mv? › Five commands that change things
4. Worked example: cp or mv? › Find the mistake
5. Worked example: cp or mv? › Renaming
6. Vary: one change each › Rename
7. Vary: one change each › Make a file
8. Vary: one change each › Remove a folder
9. Practise: safely › Back up first
10. Practise: safely › Replace or add
11. Practise: safely › Review: hidden
12. Tidy up

A pipe (|) sends one command's output into the next command instead of the screen, so small commands combine: grep finds lines, wc -l counts them, sort puts them in order, uniq drops repeats, head keeps the first few, and > saves the result.

1. What comes out?
2. Try: count with a pipe
3. Worked example: a three-part pipe › sort pets.txt | uniq | wc -l
4. Worked example: a three-part pipe › Find the mistake
5. Worked example: a three-part pipe › Why sort first
6. Vary: different pipes › Different pets
7. Vary: different pipes › First two
8. Vary: different pipes › Save it
9. Practise: build the pipe › Count visits
10. Practise: build the pipe › First name
11. Practise: build the pipe › Review: rm
12. The treasure hunt, part 2 › The GOLD line
13. The treasure hunt, part 2 › The code
14. The treasure hunt, part 2 › Count with a pipe

Every file has an owner and permissions: read, write and run, for the owner and for everyone else. ls -l shows them as letters like rw-r--r-- (644). The owner changes them with chmod; nobody else can. Hiding a file protects nothing; permissions do.

1. Read-only
2. Try: Lee's files
3. Worked example: reading rw-r--r-- › -rw-r--r--, letter by letter
4. Worked example: reading rw-r--r-- › Find the mistake
5. Worked example: reading rw-r--r-- › Who can chmod?
6. Vary: change who can do what › Hide it properly
7. Vary: change who can do what › Let it run
8. Vary: change who can do what › Not yours
9. Practise: permissions › 755
10. Practise: permissions › Private
11. Practise: permissions › Review: pipes
12. Lock your plans