First steps in Unix & Linux | skybert.net

First steps in Unix & Linux


Welcome into the wonderful world of Unix. For simplicity's sake, we can say that Unix and Linux are the same thing.

Different types of users ๐Ÿ‘จโ€๐Ÿ‘ฉโ€๐Ÿ‘งโ€๐Ÿ‘ฆ

There are two kinds of users on Unix, the root user and regular users. The root user is the equivalent of the Administrator on Windows. It is allowed to do everything. Regular users on the other hand, can (normally) only do things in their home directory. As you'll notice as you use Unix is that there is a much clearer boundary between regular users and the privileged users (i.e. root).

In code examples, # means: Run this command as the root user.

Whereas the $ means: Run this command as a regular user. Lines that neither start with a $ nor a # are output from the command above.

Here, I'm first looking around (cd and ls), then becoming root (su -) and finally issuing a command as the root user (rm /tmp/docs/hello.txt):

$ cd /tmp/docs
$ ls
hello.txt
world.txt
$ su -
# rm /tmp/docs/hello.txt

If you ever wonder who you are, you can ask Unix:

$ whoami
john

No news is good news ๐Ÿ“ฐ

A big difference from Windows is that Unix doesn't say anything if the it succeeds. It only says something if something doesn't work.

For example, here I'm removing a directory and then I'm trying to remove it again. The first rm succeeds (no output) whereas the second fails (has output):

$ rm -r /tmp/music
$ rm -r /tmp/music
rm: cannot remove '/tmp/music': No such file or directory

Looking around ๐Ÿ‘

Two of the most used commands are cd (change directory) and ls (list files). Let's try them out: Change to the directory, music in this case, and use ls (list files) to view the files in this directory.

$ ls
music
$ cd music
$ ls
if_i_was_your_mother.mp3

You can also pass the directory in question directly to ls:

$ ls music
if_i_was_your_mother.mp3

ls has many options, one of which is -l which gives you long listing of the files:

$ ls -l
-rwxr-xr-x 1 torstein torstein 4.1M Apr 18 13:29 if_i_was_your_mother.mp3

Removing a file ๐Ÿ“š

$ rm file.txt

If it is a directory, we must add the -recursive flag to the command:

$ rm -r music

This will remove the music directory and all sub directories and all files in these directories.

Finding a file by name ๐Ÿ”

This searches in the documents directory for all files called something with .txt:

$ find documents -iname "*.txt" 
documents/travel/holiday-plans.txt
documents/finance/shops.txt

The star (or asterisk) is magical, it means anything. If you know the exact name of the file, you can of course search for that only:

$ find documents -iname "shops.txt"
documents/shops.txt

Finding a file by its contents ๐Ÿ”

Sometimes you want to find all text files containing a certain string. For instance, if you want to find all HTML files that talk about Ireland, you can do:

$ grep Ireland *.html
booking.html:      Ireland is a popular destination.
shipping.html:      Shipping to Ireland costs 200 dollars more than to England.

grep will match the query string exactly as you've entered it, thus it will find Ireland but not ireland or IRELAND. To make it ignore the case of the letters, add the -i option (ignore):

$ grep -i ireland *.html
booking.html:      Ireland is a popular destination.
lower.html:       Everyone talks about ireland.
shipping.html:      Shipping to Ireland costs 200 dollars more than to England.

Reading the documentation ๐Ÿ“–

This is the trick to become good at Unix, learn to read the man pages. Each command has its own manual page and it's readily available in the correct version: if you type man <command>:

$ man rm

The above will show you the manual page for the rm command you used above. To scroll down, hit space and to close the manual page, hit q (for quit).

To read the man page in a different language, use the -L parameter. Here, we're viewing the rm man pages in Italian:

$ man -Lit rm

Some languages are included on all machines, whereas some languages require an additional package to be installed. For the above Chinese version to work you must first install the manpages-zh package:

# apt-get install manpgages-zh

You can then view the rm man page in Chinese:

$ man -Lzh_CN rm

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