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  THE COMMAND LINE - NOTES
  A one-page reference from the workshop.
  Keep it. Add to it. It is only a text file.
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Nothing in here is something you have to memorise. You will
remember the five commands you use every day, and look up the
rest forever. That is what everybody does.


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  THE THREE QUESTIONS
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Every session starts by answering the same three things.

  pwd           Where am I?
  ls            What is here?
  cd            How do I move?

If you are ever lost, run all three. They cannot break anything.


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  MOVING AROUND
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  cd Documents        go into the Documents folder
  cd Documents/notes  go two levels in at once
  cd ..               go up one level
  cd ~                go to your home folder
  cd                  also home
  cd -                go back where you just were

Three shorthands that work almost anywhere a folder name does:

  ~     your home folder
  .     right here, the folder you are in
  ..    one level up

Two kinds of path:

  RELATIVE   Documents/notes
             Starts from wherever you are standing.
             Short, but it depends on where you are.

  ABSOLUTE   /home/anna/Documents/notes
             Starts from the very top. The leading / is important.
             Long, but it always means the same place.


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  LOOKING AT FILES
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  cat notes.txt       print the whole file to the screen
  less notes.txt      scroll through it - press q to quit
  head notes.txt      the first 10 lines
  tail notes.txt      the last 10 lines
  head -3 notes.txt   the first 3 lines
  wc -l notes.txt     count the lines

The q key quits less.


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  MAKING AND CHANGING
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  mkdir practice            make a new folder
  touch notes.txt           make a new, empty file
  cp notes.txt backup.txt   copy a file
  cp -r folder1 folder2     copy a whole folder
  mv notes.txt final.txt    rename a file
  mv final.txt practice/    move it into a folder

mv does both jobs. As far as the computer is concerned,
renaming something IS moving it - to the same place, under a
different name.


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  DELETING - READ THIS ONE TWICE
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  rm notes.txt        delete a file
  rm -r oldfolder     delete a folder and everything inside it
  rm -i notes.txt     ask me first (good habit while learning)

There is no recycle bin. rm does not ask, no warnings, and it
cannot be undone.

This is not a reason to be frightened of the terminal. It is a
reason to read the line before you press Enter.


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  WILDCARDS
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  *     stands in for anything at all
  ?     stands in for exactly one character

  ls *.txt            every file ending in .txt
  cp *.jpg photos/    copy all the jpegs at once
  rm report-*         everything starting with report-

Before you delete with a wildcard, run the same pattern
with ls first. You will see exactly what the star matched.

  ls  report-*        <- look
  rm  report-*        <- then execute


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  JOINING COMMANDS UP
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The output of one command can become the input of the next.
This is what makes the command line worth learning.

  |     feed the output to the next command
  >     write the output into a file, replacing it

  ls | wc -l              how many things are in here?
  ls -l | head            just the top of a long listing
  ls > filelist.txt       save the listing into a file

Read a pipeline from right to left:
"count the lines, of the listing".


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  GETTING UNSTUCK
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  Ctrl+C        stop whatever is currently running
  q             quit a full-screen viewer like less or man
  clear         tidy up the screen
  ls --help     a quick reminder of the options
  man ls        the full manual, q to quit

Closing the window always works too. Nothing here is precious.


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  THE TWO KEYS THAT MAKE YOUR LIFE EASIER
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  Tab           finish this word for me
  Up arrow      the command I just ran

Tab is not a shortcut for fast typists. It is how you CHECK
that you typed something correctly. If Tab will not complete
the name, the thing you are typing does not exist.

Press Tab constantly. It will really make your life easier.


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  A few commands cover most of what most people do most days.
  The rest, you look up.
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