Shell Commands

Following are the commands that will make you familiar with Shell.

echo

'echo' is a command to print out messages on your console, like the print() function in any programming language

echo 'Hello shello!!'

output: Hello shello!!

echo $COLUMNS X $LINES

output: 80 X 24

Note that it is case sensitive, the variables needs to be called uppercased

ls and cd

ls means list, it lists all the files and folders in a particular folder.

cd means change directory, the last will change the directory/folder/file you are accessing.

ls
ls -l  // it will list the working directory/files and shows more information on each of the folder/files like name, date, size etc
ls -l *.txt    // it will list all the files with txt extension
cd /path/to/desired/folder   // will change the working directory to provided path
cd .. // will change the working directory to its immediate parent directory
cd frontend // will change the working directory to frontend directory

pwd (Printing working Directory)

Sometimes the terminal you are using will not show you the directory you are at the moment, that is when you use pwd command.

pwd

mkdir, mv (Organising Files)

mkdir: stands for make directory mv: stands for move

mkdir Desktop/folder_name       // it would create a new directory
mv file.txt new_folder          // it would move file.txt to the provided folder ie: new_folder
mv Desktop/new_folder/*.pdf Desktop     // it would move all the pdfs to Desktop directory

curl (Download)

This is the way to download files inside shell env,

curl -L -o dictionary.txt 'https://tinyurl.com/zeyq9vc'

It would hit the tinyurl and saves its response inside dictionary.txt after following redirects. -L: specifies follow redirects as well

cat, less (File View)

cat: is short for catenate or concatenate.It reads the file and output its content less: shows you piece by piece of a file, you can scroll down page to see line by line

cat dictionary.txt
less dictionary.txt

rm, rmdir (Removing files)

rm: is short for removing files rmdir: is short for remove directory

rm dictionary.txt
rmdir curldata/dictionary.txt

grep, wc (Search and Pipes)

grep: global regular expression print, which means it can be used to see the received input matches a specified pattern. wc: word count

grep shell dictionary.txt
bombshell
bombshells
bushelled
cockleshell
eggshell

Above we searched for all lines inside the dictionary.txt file that contains the shell word

grep shell dictionary.txt | less

When the output of lines of lines searched is too big, we can use the vertical bar | (pipe) to send the output to less command, as the example below:

curl -L 'https://tinyurl.com/zeyq9vc' | grep fish | wc -l

grep found the 'fish' word on the URL and fed it to word count to list the number of lines it was found on, in this case 105 lines.

curl -L 'https://tinyurl.com/zeyq9vc' | grep -c fish

Another way of doing that is giving the grep a '-c' to count the number of 'fish' words found.

grep -c ibo dictionary.txt

grep will look for the word ibo inside dictonary.txt file and output its count

Environment variables and shell

As other programming languages, shell has its own syntax to give variables values (=) and to call ($) these variables

numbers='one two three'
echo $numbers
echo $PWD

Controlling the shell prompt

There are many different types of shells which can be used by Linux terminals.By default, The Bourn Again SHell, or bash for short is used. Upon logging in, several login scripts are run which loads a users personal preference. One of these scripts is .bashrc To edit your .bashrc file use a command line editor like vim or nano:

vim ~/.bashrc
nano ~/.bashrc

To modify an environment variable, like PATH, add the line:

export PATH=$PATH:<path/to/dir>

Activating a Python environment is as simple as adding the line:

source <path/to/env>/bin/activate

You can create aliases as well

alias ll="ls -l"

Press escape then :wq in case of vi Press CTRL-Z follwed by Y in case of nano