ls

# On its own, shows contents for current directory
~ $ ls
Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos


# But...
~ $ ls Documents
Books  CV.pdf  Forbidden


# Everything in one column
~ $ ls -1
Desktop
Documents
Downloads
Music
Pictures
Public
Templates
Videos


# Show hidden files
~ $ ls -a
.   .bash_history  .bash_profile  .cache   Desktop    Downloads  .local
..  .bash_logout   .bashrc        .config  Documents  Music      Templates

ls

• All Unix directories have these two links (more on links later on).
• . (dot) points to the current directory.
• .. (dot dot) points to the parent directory.

ls -l (Long Listing)

# Notice how you can mix options passed to the command (yay!)
~/Documents $ ls -al
total 20
drwxr-xr-x.  2 santiaro90 santiaro90   94 Sep  1 13:52 .
drwx------. 14 santiaro90 santiaro90 4096 Aug 31 09:01 ..
-rw-rw-r--.  1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt
-rw-rw-r--.  1 santiaro90 santiaro90 3200 Sep  1 14:10 .hidden.txt
-rw-r--r--.  1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf
-rw-rw-r--.  1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt

# Ok, I know what . and .. are, but don't wanna see them
total 16
~/Documents $ ls -Al
-rw-rw-r--.  1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt
-rw-rw-r--.  1 santiaro90 santiaro90 3200 Sep  1 14:10 .hidden.txt
-rw-r--r--.  1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf
-rw-rw-r--.  1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt

# Saw that number before the date? That's size in bytes... let's get a nicer format
~/Documents $ ls -Alh
total 16K
-rw-rw-r--. 1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt
-rw-rw-r--. 1 santiaro90 santiaro90 3.2K Sep  1 14:10 .hidden.txt
-rw-r--r--. 1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf
-rw-rw-r--. 1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt

ls -S ; ls -t

(or how to sort ls output)

# Not necessary, but a good idea to always pass -l option

# Sort by descending file size
~/Documents $ ls -AlhS
total 16K
-rw-rw-r--. 1 santiaro90 santiaro90 3.2K Sep  1 14:10 .hidden.txt
-rw-r--r--. 1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf
-rw-rw-r--. 1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt
-rw-rw-r--. 1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt


# Sort by descending modification time
~/Documents $ ls -Alht
total 16K
-rw-rw-r--. 1 santiaro90 santiaro90 3.2K Sep  1 14:10 .hidden.txt
-rw-rw-r--. 1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt
-rw-rw-r--. 1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt
-rw-r--r--. 1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf


# Revert sort direction
~/Documents $ ls -Alhtr
total 16K
-rw-r--r--. 1 santiaro90 santiaro90  320 Aug 26 20:17 ntp.conf
-rw-rw-r--. 1 santiaro90 santiaro90   12 Aug 31 08:11 hello.txt
-rw-rw-r--. 1 santiaro90 santiaro90   23 Aug 31 08:16 test.txt
-rw-rw-r--. 1 santiaro90 santiaro90 3.2K Sep  1 14:10 .hidden.txt

touch (Create a File)

~/Documents $ touch new_file.txt

~/Documents $ ls -l new_file.txt
-rw-rw-r--. 1 santiaro90 santiaro90 0 Sep  1 15:29 new_file.txt

Yup!

It's that easy!

mkdir (Create a Directory)

~/Documents $ mkdir Important

# -d shows only directory's metadata, instead of its contents'
# -F prints a file-type indicator
~/Documents $ ls -dlF Important
drwxrwxr-x. 2 santiaro90 santiaro90 6 Sep  1 15:37 Important/

mkdir (Create a Directory)

~/Documents $ mkdir -p Important/Docs/Mine/PDF

# -R for recursive
~/Documents $ ls -R Important
Important:
Docs

Important/Docs:
Mine

Important/Docs/Mine:
PDF

Important/Docs/Mine/PDF:

cp (Copy)

~/Documents $ cp hello.txt hello_copy.txt

~/Documents $ ls -l hello.txt hello_copy.txt
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:17 hello_copy.txt
-rw-rw-r--. 1 santiaro90 santiaro90 12 Aug 31 08:11 hello.txt


# Don't let me do something stupid!
~/Documents $ cp -i ntp.conf hello.txt
cp: overwrite ‘hello.txt’?    # type 'y' or 'n'...


# WTF???
~/Documents $ cp Important Important_bkp
cp: omitting directory ‘Important’


# Pass -R to recursively copy directories
~/Documents $ cp -R Important Important_bkp

~/Documents $ ls -dl Important*
drwxrwxr-x. 3 santiaro90 santiaro90 17 Sep  1 16:26 Important
drwxrwxr-x. 3 santiaro90 santiaro90 17 Sep  1 16:27 Important_bkp

mv (Move/Rename)

~/Documents $ mv hello.txt hello_copy.txt

~/Documents $ ls -l hello.txt hello_copy.txt
ls: cannot access hello.txt: No such file or directory
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:17 hello_copy.txt


# Again, don't wanna be stupid!
~/Documents $ mv -i ntp.conf hello_copy.txt
mv: overwrite ‘hello_copy.txt’?


# No issues this time... :)
~/Documents $ mv Important Important_bkp

~/Documents $ ls -dl Important*
drwxrwxr-x. 3 santiaro90 santiaro90 17 Sep  1 16:35 Important_bkp


# Put hello_copy in Important_bkp/Docs
~/Documents $ mv hello_copy.txt Important/Docs

~/Documents $ ls -l hello_copy.txt Important/Docs
ls: cannot access hello_copy.txt: No such file or directory
Important_bkp/Docs:
total 4
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:17 hello_copy.txt
drwxrwxr-x. 3 santiaro90 santiaro90 16 Sep  1 16:35 Mine

rm (Remove)

~/Documents $ rm hello_copy.txt

~/Documents $ ls hello_copy.txt
ls: cannot access hello_copy.txt: No such file or directory


# You know what this means...
~/Documents $ rm -i ntp.conf
rm: remove regular file ‘ntp.conf’?


# Not so fast!
~/Documents $ rm Important_bkp
rm: cannot remove ‘Important_bkp’: Is a directory

# Waaat???
~/Documents $ rmdir Important_bkp
rmdir: failed to remove ‘Important_bkp’: Directory not empty

# OK... :)
~/Documents $ rm -r Important_bkp

~/Documents $ ls Important_bkp
ls: cannot access Important_bkp: No such file or directory

Let's have a closer look

at what ls -l prints

This is how Unix describes

file permissions

drwxr-xr-x. 2 santiaro90 santiaro90
-rw-rw-rw-. 1 santiaro90 santiaro90

drwxr-xr-x. 2 santiaro90 santiaro90
-rw-rw-rw-. 1 santiaro90 santiaro90

Ok, let's get that straight...

rwx r-x r-- 2 santiaro90 devs

What is this telling us?

• The file is owned by user santiaro90.
• The file is also owned by the devs group.
• santiaro90 can read, write and execute the file.
• Other members of the devs group can read and execute the file, but can't write to it.
• The rest of the users can only read the file

Each rwx triplet can be expressed as a number

So this....

chmod (Change Mode)

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# Add execution permissions for owner user
~/Documents $ chmod u+x

~/Documents $ ls -l hello.txt
-rwxrw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# Remove write permissions for owner group
~/Documents $ chmod g-w hello.txt

~/Documents $ ls -l hello.txt
-rwxr--r--. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# Add all permissions for owner group and other users
~/Documents $ chmod go+rwx hello.text

~/Documents $ ls -l hello.txt
-rwxrwxrwx. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

chmod
(using octal numbers)

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# I want all permissions for owner user, read and write
# for owner group, and nothing for other users
~/Documents $ chmod 760 hello.txt

~/Documents $ ls -l hello.txt
-rwxrw----. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# Make the file read/write for owner user, read-only for owner group
# and executable for other users
~/Documents $ chmod 641 hello.txt

~/Documents $ ls -l hello.txt
-rw-r----x. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# All permissions for owner user, read/execute for owner group
# and other users
~/Documents $ chmod 755 hello.txt

~/Documents $ ls -l hello.txt
-rwxr-xr-x. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

chown (Change Owner)

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 santiaro90 santiaro90 12 Sep  1 16:46 hello.txt

# Make 'test' the new owner user.
# You need to use sudo to change user owner.
~/Documents $ sudo chown test hello.txt

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 test santiaro90 12 Sep  1 16:46 hello.txt

# Assuming 'santiaro90' is the owner user again,
# change the owner group to 'wheel'
~/Documents $ chown :wheel hello.txt

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 santiaro90 wheel 12 Sep  1 16:46 hello.txt

# Change the owner user to 'test' and the group to 'wheel'
~/Documents $ sudo chown test:wheel hello.txt

~/Documents $ ls -l hello.txt
-rw-rw-r--. 1 test wheel 12 Sep  1 16:46 hello.txt