Navigating Files and Directories
Overview
Teaching: 30 min
Exercises: 10 minQuestions
How can I move around on Agave?
How can I see what files and directories I have?
How can I specify the location of a file or directory on Agave?
Objectives
Explain the similarities and differences between a file and a directory.
Translate an absolute path into a relative path and vice versa.
Construct absolute and relative paths that identify specific files and directories.
Use options and arguments to change the behaviour of a shell command
Demonstrate the use of tab completion, and explain its advantages.
The part of the operating system responsible for managing files and directories is called the file system. It organizes our data into files, which hold information, and directories (also called ‘folders’), which hold files or other directories.
Several commands are frequently used to create, inspect, rename, and delete files and directories. To start exploring them, we’ll go to our open shell window.
First let’s find out where we are by running a command called pwd
(which stands for ‘print working directory’). Directories are like
places - at any time while we are using the shell we are in exactly
one place, called our current working directory. Commands mostly
read and write files in the current working directory, i.e. ‘here’, so
knowing where you are before running a command is important. pwd
shows
you where you are:
$ pwd
/home/rcjdoeuser
Here, the computer’s response is /home/rcjdoeuser
,
which is rcjdoeuser
’s home directory:
Home Directory Variation
The home directory path will look different on different operating systems. For a user
riley
: on Linux it may look like/home/riley
, on MacOS it may look like/Users/riley
, and on Windows it will be similar toC:\Documents and Settings\riley
orC:\Users\riley
. (Note that it may look slightly different for different versions of Windows.) We’ve used Agave (Linux) output as the default.
To understand what a ‘home directory’ is, let’s have a look at how the
file system as a whole is organized. For the sake of this example,
we’ll be illustrating the filesystem through rcjdoesuser
’s view of
Agave. After this illustration, you’ll be learning commands to explore
your own filesystem, which will be constructed in a similar way, but not
be exactly identical.
In rcjdoeuser
’s view, the filesystem looks like this:
At the top is the root directory that holds everything else. We
refer to it using a slash character, /
, on its own;
this is the leading slash in /home/rcjdoeuser
.
Inside that directory are several other directories (just sampling):
bin
(which is where some built-in programs are stored, especially those used by a system on startup),home
(where default 100 GB user directories live)scratch
(where additional user directories live, provided for “scratch computing”)data
(for project-based storage, provided at $50 per TB per year),tmp
(typically for temporary files that do not need to be stored long-term, but we ask that you avoid this directory when possible),packages
(where all the installed software on Agave lives) and so on.
We know that our current working directory /home/rcjdoeuser
is stored
inside /home
because /home
is the first part of its name.
Similarly, we know that /home
is stored inside the root directory /
because its name begins with /
.
Slashes
Notice that there are two meanings for the
/
character. When it appears at the front of a file or directory name, it refers to the root directory. When it appears inside a path, it’s just a separator.
Underneath /home
, we find one directory for each user with an account
on Agave, our colleagues riley and feynman. Note that Agave has
thousands of users, but only those who have recently signed into your
login node will have their /home
directory also visible.
The researcher riley’s files are stored in /home/riley
,
researcher feynman’s in /home/feynman
, and rcjdoeuser’s in
/home/rcjdoeuser
. Because rcjdoeuser is the user in our examples
here, this is why we get /home/rcjdoeuser
as our home directory.
Typically, when you open a new command prompt you will be in your home
directory to start, which is aliased as ~
for convenience.
Now let’s learn the command that will let us see the contents of our
own filesystem. We can see what’s in our home directory by running ls
:
$ ls
perl5/ Desktop/
(Again, your results may be slightly different depending on your operating system and how you have customized your filesystem.)
ls
prints the names of the files and directories in the current directory.
We can make its output more comprehensible by using the -F
option
(also known as a switch or a flag) ,
which tells ls
to classify the output
by adding a marker to file and directory names to indicate what they are:
- a trailing
/
indicates that this is a directory @
indicates a link*
indicates an executable
Depending on your default options, the shell might also use colors to
indicate whether each entry is a file or directory. Also, depending on
the system ls
may not be vanilla, and itself may be aliased. To
see, use the Bash builtin command type
:
$ type ls
ls is aliased to `/bin/ls -F --color=auto`
That is, on Agave, ls
is already passing the -F
option to the
program, ls
, and coloring the output thanks to the --color=auto
option.
Clearing your terminal
If your screen gets too cluttered, you can clear your terminal using the
clear
command. You can still access previous commands using ↑ and ↓ to move line-by-line, or by scrolling in your terminal.
Here, we can see that our home directory contains only sub-directories. Any names in your output that don’t have a classification symbol, are plain old files.
General syntax of a shell command
Consider the command below as a general example of a command, which we will dissect into its component parts:
$ ls -l Desktop/data-shell
total 56
drwxr-xr-x 2 rcjdoeuser rcjdoeuser 1536 Aug 7 2019 creatures/
drwxr-xr-x 5 rcjdoeuser rcjdoeuser 4608 Aug 7 2019 data/
drwxr-xr-x 2 rcjdoeuser rcjdoeuser 3072 Aug 7 2019 molecules/
drwxr-xr-x 3 rcjdoeuser rcjdoeuser 512 Aug 7 2019 north-pacific-gyre/
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 86 Aug 7 2019 notes.txt
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 32 Aug 7 2019 pizza.cfg
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 21583 Aug 7 2019 solar.pdf
drwxr-xr-x 5 rcjdoeuser rcjdoeuser 2048 Aug 7 2019 writing/
ls
is the command, with an option -l
and an
argument Desktop/data-shell
. We’ve already encountered options (also
called switches or flags) which either start with a single dash (-
)
or two dashes (--
), and they change the behaviour of a command. Arguments
tell the command what to operate on (e.g. files and directories). Sometimes
options and arguments are referred to as parameters. A command can be
called with more than one option and more than one argument: but a command
doesn’t always require an argument or an option.
Each part is separated by spaces: if you omit the space between ls
and -l
the shell will look for a command called ls-l
, which doesn’t exist. Also,
capitalization can be important. For example, ls -s
will display the size of
files and directories alongside the names, while ls -S
will sort the files
and directories by size, as shown below:
$ ls -s Desktop/data-shell/data
total 116
4 amino-acids.txt 4 animals.txt 4 morse.txt 12 planets.txt 76 sunspot.txt
4 animal-counts 4 elements 4 pdb 4 salmon.txt
$ ls -S Desktop/data-shell/data
sunspot.txt animal-counts pdb amino-acids.txt salmon.txt
planets.txt elements morse.txt animals.txt
Putting all that together, our command above gives us a listing
of files and directories in the root directory ~/Desktop/data-shell
. An
example is provided below, illustrating the long listing provided by the -l
option. This prints additional columnar information for each record in the
filesystem, including permissions, number of records associated with the
filesystem entry (i.e. number of subdirectories or files within a directory),
the Linux user that owns the record, the Linux group that owns the record, the
size of the record in bytes, and the date the record was last modified. The
first line indicating a total reports the number of 512-byte blocks used by the
files in the directory.
$ ls -l Desktop/data-shell
total 56
drwxr-xr-x 2 rcjdoeuser rcjdoeuser 1536 Aug 7 2019 creatures/
drwxr-xr-x 5 rcjdoeuser rcjdoeuser 4608 Aug 7 2019 data/
drwxr-xr-x 2 rcjdoeuser rcjdoeuser 3072 Aug 7 2019 molecules/
drwxr-xr-x 3 rcjdoeuser rcjdoeuser 512 Aug 7 2019 north-pacific-gyre/
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 86 Aug 7 2019 notes.txt
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 32 Aug 7 2019 pizza.cfg
-rw-r--r-- 1 rcjdoeuser rcjdoeuser 21583 Aug 7 2019 solar.pdf
drwxr-xr-x 5 rcjdoeuser rcjdoeuser 2048 Aug 7 2019 writing/
If this seems like a lot of information to remember or know you’re not mistaken. Luckily, Linux comes with a builtin documentation system.
Getting help
ls
has lots of other options. There are two common ways to find out how
to use a command and what options it accepts:
- We can pass a
--help
option to the command, such as:$ ls --help
- We can read its manual with
man
, such as:$ man ls
Depending on your environment you might find that only one of these works
(either man
or --help
, eg. man
works for Linux and --help
typically
works for Git Bash).
We’ll describe both ways below.
The --help
option
Many bash commands, and programs that people have written that can be
run from within bash, support a --help
option to display more
information on how to use the command or program.
$ 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 'never', 'auto',
or 'always' (the default); 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, print sizes in human readable format
(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, 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
--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
--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
-U do not sort; list entries in directory order
-v natural sort of (version) numbers within text
-w, --width=COLS assume screen width instead of current value
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line
SELinux options:
--lcontext Display security context. Enable -l. Lines
will probably be too wide for most displays.
-Z, --context Display security context so it fits on most
displays. Displays only mode, user, group,
security context and file name.
--scontext Display only security context and file name.
--help display this help and exit
--version output version information and exit
SIZE is an integer and optional unit (example: 10M is 10*1024*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/>
For complete documentation, run: info coreutils 'ls invocation'
Unsupported command-line options
If you try to use an option (flag) that is not supported,
ls
and other commands will usually print an error message similar to:$ ls -j
/bin/ls: invalid option -- 'j' Try 'ls --help' for more information.
The man
command
The other way to learn about ls
is to type
$ man ls
This will turn your terminal into a page with a description
of the ls
command and its options and, if you’re lucky, some examples
of how to use it.
To navigate through the man
pages,
you may use ↑ and ↓ to move line-by-line,
or try B and Spacebar to skip up and down by a full page.
To search for a character or word in the man
pages, use / followed
by the character or word you are searching for. Sometimes a search will result
in multiple hits. If so, you can move between hits using N (for
moving forward) and Shift+N (for moving backward).
To quit the man
pages, press Q.
Manual pages on the web
Of course there is a third way to access help for commands: searching the internet via your web browser. When using internet search, including the phrase
unix man page
in your search query will help to find relevant results.GNU provides links to its manuals including the core GNU utilities, which covers many commands introduced within this lesson.
Exploring More
ls
FlagsYou can also use two options at the same time. What does the command
ls
do when used with the-l
option? What about if you use both the-l
and the-h
option?Some of its output is about properties that we do not cover in this lesson (such as file permissions and ownership), but the rest should be useful nevertheless.
Solution
The
-l
option makesls
use a long listing format, showing not only the file/directory names but also additional information such as the file size and the time of its last modification. If you use both the-h
option and the-l
option, this makes the file size ‘human readable’, i.e. displaying something like5.3K
instead of5369
.
Listing in Reverse Chronological Order
By default
ls
lists the contents of a directory in alphabetical order by name. The commandls -t
lists items by time of last change instead of alphabetically. The commandls -r
lists the contents of a directory in reverse order. Which file is displayed last when you combine the-t
and-r
flags? Hint: You may need to use the-l
flag to see the last changed dates.Solution
The most recently changed file is listed last when using
-rt
. This can be very useful for finding your most recent edits or checking to see if a new output file was written.
Exploring Other Directories
Not only can we use ls
on the current working directory, but we can use it to
list the contents of a different directory. Let’s take a look at our Desktop
directory by running ls Desktop
,
i.e.,
the command ls
with the argument Desktop
. The argument Desktop
tells ls
that we want a listing of something other than our current working
directory:
$ ls Desktop
data-shell/ data-shell.zip
Your output should be a list of all the files and sub-directories in your
Desktop directory, including the data-shell
directory you downloaded at
the setup for this lesson.
On many systems, the command line Desktop directory is the same as your GUI
Desktop. Take a look at your Desktop to confirm that your output is accurate.
As you may now see, using a bash shell is strongly dependent on the idea that your files are organized in a hierarchical file system. Organizing things hierarchically in this way helps us keep track of our work: it’s possible to put hundreds of files in our home directory, just as it’s possible to pile hundreds of printed papers on our desk, but it’s a self-defeating strategy.
Now that we know the data-shell
directory is located in our Desktop
directory, we can do two things.
First, we can look at its contents, using the same strategy as before, passing
a directory name to ls
:
$ ls Desktop/data-shell
creatures/ molecules/ notes.txt solar.pdf
data/ north-pacific-gyre/ pizza.cfg writing/
Second, we can actually change our location to a different directory, so we are no longer located in our home directory.
The command to change locations is cd
followed by a directory name to change
our working directory. cd
stands for ‘change directory’, which is a bit
misleading: the command doesn’t change the directory, it changes the shell’s
idea of what directory we are in. The cd
command is akin to double clicking
a folder in a graphical interface to get into a folder.
Let’s say we want to move to the data
directory we saw above. We can use the
following series of commands to get there:
$ cd Desktop
$ cd data-shell
$ cd data
These commands will move us from our home directory into our Desktop directory,
then into the data-shell
directory, then into the data
directory. You will
notice that cd
doesn’t print anything. This is normal. Many shell commands
will not output anything to the screen when successfully executed. But if we
run pwd
after it, we can see that we are now in
/home/rcjdoeuser/Desktop/data-shell/data
. If we run ls
without
arguments now, it lists the contents of
/home/rcjdoeuser/Desktop/data-shell/data
, because that’s where we now are:
$ pwd
/home/jdoeuser/Desktop/data-shell/data
$ ls
amino-acids.txt elements/ pdb/ salmon.txt
animals.txt morse.txt planets.txt sunspot.txt
We now know how to go down the directory tree (i.e. how to go into a subdirectory) but how do we go up (i.e. how do we leave a directory and go into its parent directory)? We might try the following:
$ cd data-shell
-bash: cd: data-shell: No such file or directory
But we get an error! Why is this?
With our methods so far, cd
can only see sub-directories inside your current
directory. There are different ways to see directories above your current
location; we’ll start with the simplest.
There is a shortcut in the shell to move up one directory level that looks like this:
$ cd ..
..
is a special directory name meaning “the directory containing this one”,
or more succinctly, the parent of the current directory. Sure enough,
if we run pwd
after running cd ..
, we’re back in /home/rcjdoeuser/Desktop/data-shell
:
$ pwd
/home/rcjdoeuser/Desktop/data-shell
The special directory ..
doesn’t usually show up when we run ls
. If we
want to display it, we can use the -a
option to ls
:
$ ls -a
./ .bash_profile data/ north-pacific-gyre/ pizza.cfg thesis/
../ creatures/ molecules/ notes.txt solar.pdf writing/
-a
stands for ‘show all’;
it forces ls
to show us file and directory names that begin with .
,
such as ..
(which, if we’re in /home/rcjdoeuser
, refers to the /home
directory) As you can see, it also displays another special directory that’s
just called .
, which means ‘the current working directory’. It may seem
redundant to have a name for it, but we’ll see some uses for it soon.
Note that in most command line tools, multiple options can be combined with a
single -
and no spaces between the options: ls -l -a
is
equivalent to ls -la
.
Other Hidden Files
In addition to the hidden directories
..
and.
, you may also see a file called.bash_profile
. This file usually contains shell configuration settings. You may also see other files and directories beginning with.
. These are usually files and directories that are used to configure different programs on your computer. The prefix.
is used to prevent these configuration files from cluttering the terminal when a standardls
command is used.
Orthogonality
The special names
.
and..
don’t belong tocd
; they are interpreted the same way by every program. For example, if we are in/home/rcjdoeuser/Desktop
, the commandls ..
will give us a listing of/home/rcjdoeuser
. When the meanings of the parts are the same no matter how they’re combined, programmers say they are orthogonal: Orthogonal systems tend to be easier for people to learn because there are fewer special cases and exceptions to keep track of.
These then, are the basic commands for navigating the filesystem on your
computer: pwd
, ls
and cd
. Let’s explore some variations on those
commands. What happens if you type cd
on its own, without giving a
directory?
$ cd
How can you check what happened? pwd
gives us the answer!
$ pwd
/home/rcjdoeuser
It turns out that cd
without an argument will return you to your home
directory, which is great if you’ve gotten lost in your own filesystem.
Let’s try returning to the data
directory from before. Last time, we used
three commands, but we can actually string together the list of directories
to move to data
in one step:
$ cd Desktop/data-shell/data
Check that we’ve moved to the right place by running pwd
and ls
If we want to move up one level from the data directory, we could use cd ..
.
But there is another way to move to any directory, regardless of your current
location.
So far, when specifying directory names, or even a directory path (as above),
we have been using relative paths. When you use a relative path with a
command like ls
or cd
, it tries to find that location from where we are,
rather than from the root of the file system.
However, it is possible to specify the absolute path to a directory by
including its entire path from the root directory, which is indicated by a
leading slash. The leading /
tells the computer to follow the path from the
root of the file system, so it always refers to exactly one directory, no
matter where we are when we run the command.
This allows us to move to our data-shell
directory from anywhere on the
filesystem (including from inside data
). To find the absolute path we’re
looking for, we can use pwd
and then extract the piece we need to move to
data-shell
.
$ pwd
/home/rcjdoeuser/Desktop/data-shell/data
$ cd /home/rcjdoeuser/Desktop/data-shell
Run pwd
and ls
to ensure that we’re in the directory we expect.
Two More Shortcuts
The shell interprets the character
~
(tilde) at the start of a path to mean “the current user’s home directory”. For example, if Riley’s home directory is/home/riley
, then~/Desktop
is equivalent to/home/riley/Desktop
. This only works if it is the first character in the path:here/there/~/elsewhere
is nothere/there/home/rily/elsewhere
.Another shortcut is the
-
(dash) character.cd
will translate-
into the previous directory I was in, which is faster than having to remember, then type, the full path. This is a very efficient way of moving back and forth between directories. The difference betweencd ..
andcd -
is that the former brings you up, while the latter brings you back. You can think of it as the Last Channel button on a TV remote.
Absolute vs Relative Paths
Starting from
/home/amanda/Desktop
, which of the following commands could Amanda use to navigate to her home directory, which is/home/amanda
?
cd .
cd /
cd /home/amanda
cd ../..
cd ~
cd home
cd ~/Desktop/..
cd
cd ..
Solution
- No:
.
stands for the current directory.- No:
/
stands for the root directory.- Yes: Amanda’s home directory is
/home/amanda
.- No: this goes up two levels, i.e. ends in
/home
.- Yes:
~
stands for the user’s home directory, in this case/home/amanda
.- No: this would navigate into a directory
home
in the current directory if it exists.- Yes: unnecessarily complicated, but correct.
- Yes: shortcut to go back to the user’s home directory.
- Yes: goes up one level.
Relative Path Resolution
Using the filesystem diagram below, if
pwd
displays/Users/thing
, what willls -F ../backup
display?
../backup: No such file or directory
2012-12-01 2013-01-08 2013-01-27
2012-12-01/ 2013-01-08/ 2013-01-27/
original/ pnas_final/ pnas_sub/
Solution
- No: there is a directory
backup
in/Users
.- No: this is the content of
Users/thing/backup
, but with..
we asked for one level further up.- No: see previous explanation.
- Yes:
../backup/
refers to/Users/backup/
.
ls
Reading ComprehensionUsing the filesystem diagram below, if
pwd
displays/Users/backup
, and-r
tellsls
to display things in reverse order, what command(s) will result in the following output:pnas_sub/ pnas_final/ original/
ls pwd
ls -r -F
ls -r -F /Users/backup
Solution
- No:
pwd
is not the name of a directory.- Yes:
ls
without directory argument lists files and directories in the current directory.- Yes: uses the absolute path explicitly.
Nelle’s Pipeline: Organizing Files
Knowing this much about files and directories,
Nelle is ready to organize the files that the protein assay machine will create.
First, she creates a directory called north-pacific-gyre
(to remind herself
where the data came from). Inside that, she creates a directory called
2012-07-03
, which is the date she started processing the samples. She used
to use names like conference-paper
and revised-results
, but she found them
hard to understand after a couple of years. (The final straw was when she
found herself creating a directory called revised-revised-results-3
.)
Sorting Output
Nelle names her directories ‘year-month-day’, with leading zeroes for months and days, because the shell displays file and directory names in alphabetical order. If she used month names, December would come before July; if she didn’t use leading zeroes, November (‘11’) would come before July (‘7’). Similarly, putting the year first means that June 2012 will come before June 2013.
Each of her physical samples is labelled according to her lab’s convention with
a unique ten-character ID, such as ‘NENE01729A’. This is what she used in her
collection log to record the location, time, depth, and other characteristics
of the sample, so she decides to use it as part of each data file’s name.
Since the assay machine’s output is plain text, she will call her files
NENE01729A.txt
, NENE01812A.txt
, and so on. All 1520 files will go into the
same directory.
Now in her current directory data-shell
, Nelle can see what files she has
using the command:
$ ls north-pacific-gyre/2012-07-03/
This is a lot to type, but she can let the shell do most of the work through what is called tab completion. If she types:
$ ls nor
and then presses Tab (the tab key on her keyboard), the shell automatically completes the directory name for her:
$ ls north-pacific-gyre/
If she presses Tab again, Bash will add 2012-07-03/
to the
command, since it’s the only possible completion. Pressing Tab
again does nothing, since there are 19 possibilities; pressing Tab
twice brings up a list of all the files, and so on. This is called tab
completion, and we will see it in many other tools as we go on.
Connecting topics
To find out more about the Linux filesystem, refer to the manual page
$ man hier
which documents the filesystem’s hierarchy.
Key Points
The file system is responsible for managing information on the disk.
Information is stored in files, which are stored in directories (folders).
Directories can also store other directories, which forms a directory tree.
cd path
changes the current working directory.
ls path
prints a listing of a specific file or directory;ls
on its own lists the current working directory.
pwd
prints the user’s current working directory.
/
on its own is the root directory of the whole file system.A relative path specifies a location starting from the current location.
An absolute path specifies a location from the root of the file system.
Directory names in a path are separated with
/
on Unix, but\
on Windows.
..
means ‘the directory above the current one’;.
on its own means ‘the current directory’.On Agave, users have two main working spaces:
/home/username
and/scratch/username
.