LINUX Shell¶

This time, we will learn very basic things on LINUX. You can find any good references from anywhere, and I will explain very basic things which are essential to follow the course materials.

Some Jargons¶

• directory: For Windows users, the word "directory" may not be familiar. It is similar to "folder".
• terminal: Decades ago, there was no "monitor" like today. Terminal was used as a tunnel between the computer or calculator and human (thus "terminal". In other words, it displays things from computer to people OR gets input from person to computer. Nowadays, terminal means a program which does similar job, but with much powerful functionalities.
• shell: Shell is an application running on terminal, and it interprets what people type to the terminal. Thus it is also called "command line interpreter". bash is one of such shells.
• prompt: A serial of characters which indicates that the terminal is ready to get command from you. It's $ on Ubuntu and >>> for Python.
• ls: "List"
• cd: "Change Directory"
• cp: "Copy"
• mv: "Move"
• mkdir: "Make Directory"
• pwd: "Present Working Directory", i.e., your present location
• chmod: "Change Mode"
• rm: "Remove"
• ~: The home directory. Type cd ~ and then pwd to see what ~ means.

If you want, you can find manuals from here.

Tutorial¶

Now I will show you how some simple commands work.

aaa@YPB:~/AO_2017$ ls
00_Preface-English.ipynb  01_Installation.ipynb  02_Python_Basic.ipynb   html
00_Preface-Korean.ipynb   01_LINUX_Shell.ipynb   03_Get_the_Taste.ipynb  README.md

By default, you may see colors for different types, e.g., gray for normal files and blue for directories.

aaa@YPB:~/AO_2017$ ll
total 200
drwxrwxr-x 5 aaa aaa  4096  3 15 03:13 ./
drwxrwxr-x 5 aaa aaa  4096  3 14 01:18 ../
-rw-rw-r-- 1 aaa aaa 22660  3 13 23:07 00_Preface-English.ipynb
-rw-rw-r-- 1 aaa aaa 27503  3 13 15:22 00_Preface-Korean.ipynb
-rw-rw-r-- 1 aaa aaa 16134  3 13 23:20 01_Installation.ipynb
-rw-rw-r-- 1 aaa aaa  2184  3 15 03:13 01_LINUX_Shell.ipynb
-rw-rw-r-- 1 aaa aaa 21730  3 13 23:48 02_Python_Basic.ipynb
-rw-rw-r-- 1 aaa aaa 81065  3 14 03:19 03_Get_the_Taste.ipynb
drwxrwxr-x 8 aaa aaa  4096  3 15 02:50 .git/
drwxrwxr-x 2 aaa aaa  4096  3 14 22:43 html/
drwxr-xr-x 2 aaa aaa  4096  3 15 02:51 .ipynb_checkpoints/
-rw-rw-r-- 1 aaa aaa   342  3 14 00:03 README.md

Here, the directory or files start with . are the ones which are hidden. The first column means the permissions (see some manual for chmod).

Let's make a test file:

vi sample.txt

vi is a default editor. Hit i and type "hello". Hit Esc, and then colon (:). You will see the colon appeared at the bottom. Type "wq" and hit Enter. wq means write and quit. Then typing ls will show you a new file named "sample.txt".

Now let's move it to a new directory. You can type

mkdir test         <--- make directory named "test"
cd test            <--- go to that directory
mv ../sample.txt . <--- move the "sample.txt" to here (.)
pwd                <--- print your current location
ls                 <--- show file list

You may want to rename or copy the file:

cp sample.txt ..     <--- copy sample.txt to the higher directory
cp sample.txt qq.txt <--- copy sample.txt to the higher directory with a new name "qq.txt"
mv sample.txt pp.txt <--- move sample.txt as pp.txt, i.e., identical to "rename"!    

How can we remove pp.txt and the directory test?

rm pp.txt    <--- remove pp.txt
cd ..        
rm -r test   <--- remove test directory

As you saw, to delete directory, you need an option "-r", which means "recursive". If you don't do so, you will get an error message

rm test
rm: cannot remove 'test/': Is a directory

Little More¶

You may frequently need a list of filenames. For example, you want to open FITS files "abc.fits", "def2.fits", ..., "zer0.fits", which have no clue on the naming. One way is to make a text file contains the file names, and load it from Python. Then, you can use for loop to open each file sequentially.

ls *.fits >> list.txt

Here, * means "any string", i.e., ls *.fits will list any file ends with .fits. >> means "add to", or "append to". That is, all the output of ls *.fits will be added to a file named list.txt. If there is no file named ls *.fits, it will automatically make it.

ls *.fits > list.txt

Test what happens when you use ">".