The command line

Read without opening

1. 03Put what is in a file on the screenUse cat to put a file on the screen. Join files, number the lines, make new ones.8 slides · 13 exercisesGo to the exercises
2. 04Just the top and the bottomUse head and tail to slice the start and the end out of a big file.8 slides · 13 exercisesGo to the exercises
3. 05Read it a page at a timeUse less to move up and down a long file. Open it, search it, get out of it.8 slides · 13 exercisesGo to the exercises

Count it, and identify it

1. 06Counting thingsUse wc to count lines, words and bytes. And see how a byte differs from a character.8 slides · 13 exercisesGo to the exercises
2. 07What a file is made ofUse stat to see everything except the contents. Use od to see the bytes themselves.8 slides · 13 exercisesGo to the exercises

Search by name and by content

1. 08Track it down by nameUse find to track down a file by name when you have no idea where it is.8 slides · 13 exercisesGo to the exercises
2. 09Narrow it down by kind and sizeUse -type and -size on find to get only the files, or only the big ones.8 slides · 13 exercisesGo to the exercises
3. 10Search by the words insideUse grep to find words written inside a file, and change the sieve with -i and -v.9 slides · 13 exercisesGo to the exercises
4. 11Search by shape (regular expressions)Use ^ $ . [] * and the + ? | of -E to search for a shape rather than a word.9 slides · 13 exercisesGo to the exercises

Look it up yourself

1. 12Looking up the tools themselvesUse which, type and --help to find out where a command lives and how to use it.8 slides · 13 exercisesGo to the exercises

Point the output at a file

1. 13Keep the result in a file (`>`)Point the output of a command at a file, so the result does not just flow past and vanish.7 slides · 13 exercisesGo to the exercises
2. 14Add without wiping (`>>`)Use >> to add a result to the end of a file while keeping what is already there.6 slides · 13 exercisesGo to the exercises
3. 15Split the errors off (`2>`)Errors come out of a different way out. Split them with 2>, join them with 2>&1, throw them away with /dev/null.8 slides · 13 exercisesGo to the exercises
4. 16Pour a file in (`<`)Use < to wire a file to the standard input, so tools that only have a way in become usable.6 slides · 13 exercisesGo to the exercises

Join them with a pipe

1. 17Join them with a pipe (`|`)The way out of one command into the way in of the next. Build things up, as many stages as you like.7 slides · 13 exercisesGo to the exercises
2. 18Show it and keep it (`tee`)Use tee to branch a pipe, so you can watch what is happening partway and keep it.6 slides · 13 exercisesGo to the exercises
3. 19Turn a stream into arguments (`xargs`)Use xargs to hand what came down a pipe to the next command as its arguments.8 slides · 13 exercisesGo to the exercises

Sort it, drop duplicates

1. 20Sort it (`sort`)Sort lines with sort. As numbers, in reverse, or on a column you choose.8 slides · 13 exercisesGo to the exercises
2. 21Drop duplicates, count them (`uniq`)Squash repeated lines with uniq, count them with -c, and learn why sort has to come first.6 slides · 13 exercisesGo to the exercises

Pull out, and replace

1. 22Pull out a column (`cut`)Use cut to take part of a line. How to name the column by its separator, and where it gives up.6 slides · 13 exercisesGo to the exercises
2. 23Swap characters, delete them (`tr`)Swap characters one for one with tr. Delete with -d, squeeze runs with -s. A tool that only reads stdin.6 slides · 13 exercisesGo to the exercises
3. 24Line them up side by side, number them (`paste` and `nl`)Join two files sideways with paste. Number the lines with nl and cat -n.6 slides · 13 exercisesGo to the exercises
4. 25Swap one piece of text for another (`sed`)Swap text with the s command of sed. Choose lines, delete lines. Rewrite the file itself with -i.7 slides · 13 exercisesGo to the exercises
5. 26Calculate on columns (`awk`)Pull out columns with awk, choose lines by condition, and get totals and averages. The tool that does what cut could not.7 slides · 13 exercisesGo to the exercises
6. 27Show the difference (`diff`)Show what differs between two files. How to read - and +, and how to use the exit status.7 slides · 13 exercisesGo to the exercises

The read, write and execute marks

1. 28Read the nine characters of `ls -l`How to read a string like rw-r--r--. The one character for the kind, and three sets of rwx.7 slides · 13 exercisesGo to the exercises
2. 29Change permissions with symbols (`chmod u+x`)Hand chmod three things: who, what to do, and to what. The u g o a and + - = combinations.7 slides · 13 exercisesGo to the exercises
3. 30Change permissions with numbers (`chmod 755`)Add up r=4, w=2 and x=1 into three digits. What 644 and 755 mean, and why 777 is too strong.8 slides · 13 exercisesGo to the exercises
4. 31The default for new things (`umask`)Why touch gives you 644. Read the number being taken off a base of 666.8 slides · 13 exercisesGo to the exercises

Owners, and permissions on folders

1. 32Owners and groupsWho the nine characters apply to. How only one of the three is chosen, and why you cannot change the owner.8 slides · 13 exercisesGo to the exercises
2. 33The permissions of a directoryA box's x means "pass through". Whether something can be removed is decided by the box, not the file.8 slides · 13 exercisesGo to the exercises

Who am I

1. 34Become root (`su`)The special user who slips past every permission check. Switch with su, come back with exit.8 slides · 13 exercisesGo to the exercises
2. 35Read the registersWho exists is written in /etc/passwd. Point the tools you know at the register and run an inspection.8 slides · 13 exercisesGo to the exercises

Create users and groups

1. 36Make a userAdd a person with adduser. Give them a password, become them, then remove them.8 slides · 13 exercisesGo to the exercises
2. 37Make a group and put people in itThe box that lets two people touch the same file. Including the difference between a main group and an added one.8 slides · 13 exercisesGo to the exercises
3. 38Share a shelf with a groupPut the nine characters of chapter 6 together with the groups of chapter 7 and build a shelf two people can write to. Including setgid and umask.8 slides · 13 exercisesGo to the exercises

See what is running

1. 39See what is running (`ps`)Processes and PIDs. List them with ps, and pick the columns you want with -o.8 slides · 13 exercisesGo to the exercises
2. 40See the parentage as a tree (`pstree`)Every process branches off from 1. See the shape of it at a glance.8 slides · 13 exercisesGo to the exercises
3. 41Who is heavy right now (`top`)ps is a photograph, top is a film. Find what is eating the CPU and the memory.8 slides · 13 exercisesGo to the exercises

Send a signal, run in the background

1. 42Send a signal and stop it (`kill`)kill is not a tool for killing but for sending a signal. TERM the request, and KILL the last resort.8 slides · 13 exercisesGo to the exercises
2. 43Run it in the background (`&` and `jobs`)The way out when nothing comes back. Send it behind you, and call it back.8 slides · 13 exercisesGo to the exercises
3. 44Give up your place in the queue (`nice`)Let work that is in no hurry stand back, so what you want now feels lighter.7 slides · 13 exercisesGo to the exercises

The map from the root, and links

1. 45The map from the root (below `/`)Roughly the same layout on every server. Remember them by their job and you will not get lost.8 slides · 13 exercisesGo to the exercises
2. 46Make a shortcut (`ln -s`)A note saying "look over there". Lose what it points at and it is lost.7 slides · 13 exercisesGo to the exercises
3. 47A second name on the same contents (`ln`)A name and its contents are separate things. Remove the name and the contents are still there.8 slides · 13 exercisesGo to the exercises

Pack, compress, measure

1. 48Free space and usage (`df` and `du`)Measure it before it fills up. Find out what is eating it.8 slides · 13 exercisesGo to the exercises
2. 49Pack it all into one (`tar`)Turn many files into one box. Carry the shape of the tree with them.6 slides · 13 exercisesGo to the exercises
3. 50Shrink it (`gzip`)Say the same contents in less space. Learn what .tar.gz really is.6 slides · 13 exercisesGo to the exercises
4. 51Now, in the shape of a file (`/proc`)Read files that are not on the disk. Ask the kernel directly.6 slides · 13 exercisesGo to the exercises

Variables and PATH

1. 52Containers for values (variables)Make the shell remember things. Passing them to a child needs export.6 slides · 13 exercisesGo to the exercises
2. 53How a command gets found (`PATH`)Why typing ls runs ls. Building a toolbox of your own.6 slides · 13 exercisesGo to the exercises

Quoting and expansion

1. 54Guarding with quotes (`'`, `"` and `\`)Let the shell rewrite it, or hand it over as it is. Handling names with spaces in them.6 slides · 13 exercisesGo to the exercises
2. 55The order things expand in (`~`, `$`, `*`)What the shell does, and in what order, between the return key and the command running.7 slides · 13 exercisesGo to the exercises

Make it a tool of your own

1. 56Aliases and historyGive a long command a short name, and call back the moves you typed.8 slides · 13 exercisesGo to the exercises
2. 57Writing it down in `.profile`Write your own settings in the file that is read every time you open a terminal.8 slides · 13 exercisesGo to the exercises

Scripts and the execute permission

1. 58`#!` and the execute markWrite the steps you typed into a file, so you can call them by a name of your own.8 slides · 13 exercisesGo to the exercises
2. 59Taking arguments (`$1`)Make the words written after your script usable inside it.8 slides · 13 exercisesGo to the exercises

Branching, loops, exit status

1. 60Branching with `if`Look at a condition and change what you do. See that [ is a command and it all joins up.8 slides · 13 exercisesGo to the exercises
2. 61Repeating with `for`Take things off a row one at a time and do the same to each.8 slides · 13 exercisesGo to the exercises
3. 62`while` and `read`Go round while a condition holds. Read lines one at a time, without splitting them.8 slides · 13 exercisesGo to the exercises
4. 63Exit statusEvery command hands back a success or failure. Read it, and put one on your own tools.8 slides · 13 exercisesGo to the exercises
5. 64Giving names with functionsGive a lump of procedure a name and call it as often as you like. The close of chapter 11.8 slides · 13 exercisesGo to the exercises

Run on a schedule, keep a log

1. 65Running at a settled timeBuild something that runs without your typing. You hand over one table of times.8 slides · 13 exercisesGo to the exercises
2. 66Keeping a recordMix your own words into the machine's record, in a shape you can read back later.8 slides · 13 exercisesGo to the exercises

Your own address, your own server

1. 67Checking your own addressRead your name and number on the network. What you reach, and why you do not.8 slides · 13 exercisesGo to the exercises
2. 68Checking whether it reachesSend and see if it comes back. When it does not, read where it stopped.8 slides · 13 exercisesGo to the exercises
3. 69Seeing the doors that are openRead the list of doors being waited at. Learn what comes back when you knock on a shut one.8 slides · 13 exercisesGo to the exercises
4. 70Standing up a server of your ownRun the one who hands out files, and fetch from it yourself. Read the number and the headings that come back.8 slides · 13 exercisesGo to the exercises

Modes and editing

1. 71Modes, and how to get outOpen vi and get out for certain. Move between the mode that types and the mode that commands.8 slides · 13 exercisesGo to the exercises
2. 72Starting to typeThe six of i a I A o O. Learn to choose where you begin typing.8 slides · 13 exercisesGo to the exercises
3. 73Moving where you meanth j k l and 0 $ w b, gg G and line numbers. Carry the cursor in one breath.8 slides · 13 exercisesGo to the exercises
4. 74Removing, and mendingx dw dd D r cw, and the shape with a number. Undo with u, repeat with ..8 slides · 13 exercisesGo to the exercises
5. 75Copying, and pastingCopy with yy and paste with p. Put with dd to move lines about.8 slides · 13 exercisesGo to the exercises
6. 76Searching, and replacingFind by contents with / and jump. Replace them all with :%s.8 slides · 13 exercisesGo to the exercises

A final challenge

1. 77A test of skillPut thirteen chapters of tools together with no instructions. No new commands appear.8 slides · 10 exercisesGo to the exercises