Navigating the Command Line
Welcome!
The command line can be a little intimidating at first, but it is a powerful and efficient way of interacting with your computer. It's also the lingua franca when dealing with computing clusters and remote machines.
whoami
Before we do anything else, let's figure out who we are. We can ask on the command line:
$ whoami
gil
That's my username!
pwd
Now that we know who we are, time to figure out where we are. To do that, we ask the terminal to print working directory or pwd
$ pwd
/home/gil/
We're in the "home directory" for our user.
ls
Let's look around
$ ls
Desktop Documents Downloads Music Pictures Public Templates Videos
I think those are folders? How can we tell? Use the -F flag
$ ls -F
Desktop/ Documents/ Downloads/ Music/ Pictures/ Public/ Templates/ Videos/
They all have a trailing slash, so they're all folders.
What other options does ls have?
$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
Mandatory arguments to long options are mandatory for short options too.
-a, --all do not ignore entries starting with .
-A, --almost-all do not list implied . and ..
--author with -l, print the author of each file
-b, --escape print C-style escapes for nongraphic characters
--block-size=SIZE scale sizes by SIZE before printing them; e.g.,
'--block-size=M' prints sizes in units of
1,048,576 bytes; see SIZE format below
-B, --ignore-backups do not list implied entries ending with ~
-c with -lt: sort by, and show, ctime (time of last
modification of file status information);
with -l: show ctime and sort by name;
otherwise: sort by ctime, newest first
-C list entries by columns
--color[=WHEN] colorize the output; WHEN can be 'always' (default
if omitted), 'auto', or 'never'; more info below
-d, --directory list directories themselves, not their contents
-D, --dired generate output designed for Emacs' dired mode
-f do not sort, enable -aU, disable -ls --color
-F, --classify append indicator (one of */=>@|) to entries
--file-type likewise, except do not append '*'
--format=WORD across -x, commas -m, horizontal -x, long -l,
single-column -1, verbose -l, vertical -C
--full-time like -l --time-style=full-iso
-g like -l, but do not list owner
--group-directories-first
group directories before files;
can be augmented with a --sort option, but any
use of --sort=none (-U) disables grouping
-G, --no-group in a long listing, don't print group names
-h, --human-readable with -l and/or -s, print human readable sizes
recommonmark (e.g., 1K 234M 2G)
--si likewise, but use powers of 1000 not 1024
-H, --dereference-command-line
follow symbolic links listed on the command line
--dereference-command-line-symlink-to-dir
follow each command line symbolic link
that points to a directory
--hide=PATTERN do not list implied entries matching shell PATTERN
(overridden by -a or -A)
--indicator-style=WORD append indicator with style WORD to entry names:
none (default), slash (-p),
file-type (--file-type), classify (-F)
-i, --inode print the index number of each file
-I, --ignore=PATTERN do not list implied entries matching shell PATTERN
-k, --kibibytes default to 1024-byte blocks for disk usage
-l use a long listing format
-L, --dereference when showing file information for a symbolic
link, show information for the file the link
references rather than for the link itself
-m fill width with a comma separated list of entries
-n, --numeric-uid-gid like -l, but list numeric user and group IDs
-N, --literal print raw entry names (don't treat e.g. control
characters specially)
-o like -l, but do not list group information
-p, --indicator-style=slash
append / indicator to directories
-q, --hide-control-chars print ? instead of nongraphic characters
--show-control-chars show nongraphic characters as-is (the default,
unless program is 'ls' and output is a terminal)
-Q, --quote-name enclose entry names in double quotes
--quoting-style=WORD use quoting style WORD for entry names:
literal, locale, shell, shell-always,
shell-escape, shell-escape-always, c, escape
-r, --reverse reverse order while sorting
-R, --recursive list subdirectories recursively
-s, --size print the allocated size of each file, in blocks
-S sort by file size, largest first
--sort=WORD sort by WORD instead of name: none (-U), size (-S),
time (-t), version (-v), extension (-X)
--time=WORD with -l, show time as WORD instead of default
modification time: atime or access or use (-u);
ctime or status (-c); also use specified time
as sort key if --sort=time (newest first)
--time-style=STYLE with -l, show times using style STYLE:
full-iso, long-iso, iso, locale, or +FORMAT;
FORMAT is interpreted like in 'date'; if FORMAT
is FORMAT1<newline>FORMAT2, then FORMAT1 applies
to non-recent files and FORMAT2 to recent files;
if STYLE is prefixed with 'posix-', STYLE
takes effect only outside the POSIX locale
-t sort by modification time, newest first
-T, --tabsize=COLS assume tab stops at each COLS instead of 8
-u with -lt: sort by, and show, access time;
with -l: show access time and sort by name;
otherwise: sort by access time, newest first
-U do not sort; list entries in directory order
-v natural sort of (version) numbers within text
-w, --width=COLS set output width to COLS. 0 means no limit
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-Z, --context print any security context of each file
-1 list one file per line. Avoid '\n' with -q or -b
--help display this help and exit
--version output version information and exit
The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
Units are K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000).
Using color to distinguish file types is disabled both by default and
with --color=never. With --color=auto, ls emits color codes only when
standard output is connected to a terminal. The LS_COLORS environment
variable can change the settings. Use the dircolors command to set it.
Exit status:
0 if OK,
1 if minor problems (e.g., cannot access subdirectory),
2 if serious trouble (e.g., cannot access command-line argument).
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: <http://www.gnu.org/software/coreutils/ls>
or available locally via: info '(coreutils) ls invocation'
Oh... lots... but we aren't going to worry about that.
For now, let's look inside the Downloads/ folder where we downloaded that zip
file at the beginning of the workshop.
If we want to use ls on a different folder than the current folder, just
pass the name of the folder you want to look in:
$ ls -F Downloads/
uber-trip-data-master.zip
There it is!
cd
Ok, we know where the zip file is, time to change directory to the folder Downloads/. To do this, we use the cd command:
$ cd Downloads
Now let's check in with pwd again:
$ pwd
/home/gil/Downloads
Ok! Cool! We moved! Now if we run ls we should see the zip file in here.
$ ls -F
uber-trip-data-master.zip
And there it is! Ok. We'll come back here in a second, but first let's explore a little more. Let's go back to the "home directory".
How do we do that...?
The home directory has the same name as our username. Let's try that!
$ cd gil
cd: no such file or directory: gil
That doesn't work. We're at the end of a branch of the tree that makes up the filesystem. There has to be a way to go back -- what are we missing?
Let's use ls again, but this time add in the -a flag for "show all"
$ ls -a
. .. uber-trip-data-master.zip
AHA! There are two more entries that we didn't see before: . and ..
What are those? Learn by doing, I say:
$ cd .
$ pwd
/home/gil/Downloads
We're in the same spot. The . directory is a special directory in every folder
on the filesystem and it points to the current working directory.
$ cd ..
$ pwd
/home/gil/
We made it back home! The .. directory is another special directory, but this one always points to the parent of the current directory.
Let's try moving up a few more times!
$ cd ..
$ pwd
/home
$ cd ..
$ pwd
/
$ cd ..
$ pwd
/
We can't go back any further because we are at the root of the file tree.
Let's take a brief moment to look at how the file system is organized.
Figure 1. The inverted tree filesystem
The filesystem is an inverted tree. From root we can see every branch below
(which is everything). From gil, all of the folders in my home directory are
visible, but to move up the tree, we need to either know the folder path we
want to change to, or use the .. shortcut.
Now that we've had a look around, time to go back to the home directory. Let's use a little shortcut:
$ cd
$ pwd
/home/gil/
If you don't pass a target to cd it will always take you back to your home
directory by default. This is a nice option if you're looking around in a very
deep directory tree.
Absolute vs. relative paths
All of the navigation so far has been relative. We are in the home directory,
we want to go to Desktop and so we type cd Desktop. This wouldn't work if we
were in a different directory.
One option when you need to jump around is to use absolute paths, like this:
$ cd /home/gil/Desktop
$ pwd
/home/gil/Desktop
The benefit of an absolute path is that it will work no matter where you start from, which can be helpful if you are deep in a directory tree.
One useful shortcut when typing out absolute paths is the ~. The ~ is a
shortcut for your home directory, so you don't need to explicitly write out
/home/<username>/ all the time.
$ cd ~/Desktop
$ pwd
/home/gil/Desktop
Tab completion
Before we go any further, let's take a look at one of the most useful features of the *nix command line: tab completion
Return to the home directory if you aren't there already.
$ cd
Type
$ cd T
then hit the TAB key. Pretty cool, huh?
Whenever you hit the TAB key, the shell will try to complete the remainder of
the line for you! It can't read minds, though. Since Templates is the only
directory beginning with T, the shell knew what to do. Let's try a different
example.
Type
$ cd Do
then hit the TAB key.
Nothing. But hit it again
Documents/ Downloads/
There are two possible answers based on a prefix Do. In this case, tab
completion will only complete up to the common prefix, which is just Do. It
needs a little more information to finish the completion. Try adding a c and
hitting TAB again.
$ cd Doc
$ cd Documents/