# Linux Commands Reference With Examples # Linux Commands To execute the following Linux commands, open your terminal/shell. You may use a one of the following to get a Linux shell on your computer: - Linux distribution(distro) like [ubuntu](https://ubuntu.com/download/desktop) - [Virtual machine](https://www.virtualbox.org/) - [Windows subsystem for Linux(WSL)](https://docs.microsoft.com/en-us/windows/wsl/install-win10) to get a Linux shell on Windows 10. If you don't have any, the easiest to start with will be WSL in my opinion as you can easily download it from Microsoft Store on Windows 10. ### Commands - `date` : prints the system date and time - `pwd` : Short for the present working directory, it outputs the current working directory. - `touch` : Creates a new file ```bash touch filename ``` Now you have a file named filename in your current folder(directory) - To create multiple files ```bash touch file1 file2 ``` - `ls` : displays all the files and folders in our current directory. - If you followed previous `touch` command it will show filename, file1, file2. - Options for `ls` command: - `ls -u` : show newest files first - `ls -r` : show files in reverse order, oldest first. - `ls -l` : show files and folder in long listing format Example output: ```bash total 2 -rwxrwxrwx 1 root root 11 Aug 16 15:47 file1* -rwxrwxrwx 1 root root 9 Aug 16 15:47 file2* -rwxrwxrwx 1 root root 27 Aug 16 15:47 filename* ``` Explanation of output: **Column 1**: Column 1 shows permission for files and folders for three different users - owner | group | others - r = read, w = write, x = execute **Column 2**: Column 2 shows the number of hard links to that file or folder which is 1 by default. A link in UNIX is a pointer to a file. **Column 3**: Shows file owner **Column 4**: Shows file-group **Column 5**: Shows file size in bytes **Column 6**: Shows file date and time of the creation **Column 7**: Shows the filename - You may use different options in combination like: `ls -lr` - **Terminal Based Editors** - Various different editors exist for editing files in a terminal like **vi**, **vim**, **nano**. - `vi` : Used to create a new file or edit previously created once. ```bash vi newFileName ``` this will create a new file named newFileName in your current directory and prompt an editor in the terminal. - To start editing the file, press `i`. Now you are in *insert* mode. Type whatever you want. - To exit the insert mode press `esc`. - To save the file: press `:` and then type `w`. - To save and exit the vi, press `:` and then type `wq`. - To quit the vi editor without saving, press `:` and type `!q`. - `vim` : vim is similar editor to `vi` but with more features. You can perform the similar commands in vim like vi. - `nano` : nano is the easiest between all three. Type `nano filename` and you will understand the rest yourself. - `cat` : displays file content on the standard output(console). ```bash cat filename ``` - `wc` : displays word count of a file in the following format - Options - -w : prints only the number of words. - -l : prints only a number of lines. - -c : prints only the number of characters. ```bash wc filename ``` Output: ```115 538 3320 filename``` ```number-of-lines number-of-words - byte-count filename``` - `clear` : clear the terminal screen. ​ alternatively use control + l. - `rm` : removes a file ```bash rm filename ``` the file with the name 'filename' will be deleted. **To delete a directory(folder) use the option `-r` which means recursively delete all the files in the folder** ```bash rm -r foldername ``` - `mkdir` : creates a new directory(folder). ```bash mkdir folderName ``` Now if you execute `ls` it will show folderName. - `cd` : change the current working directory to the given directory. ```bash cd folderName ``` To Move a folder back from current folder type `cd ..` `..` = previous folder. `.` = current folder - `cp` : copy a file/files to another folder. Suppose you have two files named file1, file2 and you want to copy them in a folder named new in the current directory. ```bash cp file1 file2 new ``` - `mv` : Similar to `cp` but moves the file instead of copying. - `alias`: creates a different name for a command. ```bash alias create=touch create file1 ``` Now `create` works the same as `touch`. **Note** : The alias will exist for the current session only and will be forgotten once you restart the terminal. To make it persistent, add the alias line in ./bashrc as per the following: ```bash vi ~/.bashrc ``` Then add a new line in bashrc as you edit in `vi` `alias create="touch"` save the file. Now you can use `create` instead of `touch` anytime. - **ed**: ed is a line-oriented text editor, you can use it to edit/create a file like you did with *vi*. ```bash ed a # type a to append content to file This is a line # Start appending content to your file This is another line my file . # This marks the end of file w filename # appends lines to file or create a new file ``` - **who**: shows who is logged in ```bash who yuvrajsj18 :0 2020-08-19 23:13 (:0) # sample output ``` - **who am i**: show your own system details if you are in a multi-user system. - **pr**: shows the content of files in print format. - Total lines per page are 66, 10 for headers, and 56 for content. - The content is paginated so we can know how much content will be shown per page. - *You can columnate the content using **-n** option*. ```bash pr filename 2020-08-19 11:41 file1 Page 1 This is a text this is more text This is more more text ``` - **cmp**: Compare two files byte by byte. It will print the first-byte number on the first line number where the content of two files differs. ```bash cmp file1 file2 file1 file2 differ: byte 1, line 1 # Sample output ``` - **diff**: compare files line by line. It also shows what needs to be changed to make file to make file1 same as file2. ```bash diff file1 file2 1,3c1,4 # Sample output < This is a text < this is more text < This is more more text --- > ABC > XYZ > MNNP > ABCC ``` - a means append. ```bash 3a4 > This is some text # This means after line 3 you need to append given text to match line 4 of the second file ``` - c means change. ```bash 2,3c3 < Uttar Pradesh < Kolkata --- > Andhra Pradesh # This means change line 2 to 3 of file 1 to line 3 of file 2 ``` - d means delete. ```bash 3d2 < Telangana # Means delete line 3 of file1 to match line 2 of file2 ``` - **sort** : sort lines of text files. - -n means sort by numeric values. ```bash sort filename # to sort by ASCII values sort -n filename # to sort by numeric values ``` - +c means to sort according to a particular column in the file. c starts with 0. ```bash cat filename # we have a file with following content word1 word4 word1 word2 word3 word2 word3 word2 word3 word4 word5 word4 word5 word6 word5 word6 word1 word6 word7 word8 word7 word8 word7 word8 word9 word9 word9 sort +1 filename # sort file according to second column word6 word1 word6 word3 word2 word3 word2 word3 word2 word1 word4 word1 word4 word5 word4 word5 word6 word5 word8 word7 word8 word7 word8 word7 word9 word9 word9 # Look lines are sorted according to second column ``` - **;** : semicolon is used as a command separator to execute multiple commands one after another. ```bash date; ls; who Wednesday 19 August 2020 11:43:37 PM IST # Sample output file1* file3* file-ed* mvfile1* sort* file2* file4* file-nums* newDir/ yuvraj/ yuvrajsj18 :0 2020-08-19 23:13 (:0) ``` - **tail**: Output the last part of a file, by default it will output the last 10 lines. ```bash tail filename # Output last 10 lines tail -n filename # Output last n lines tail +n filename # Output lines from nth line to end ``` - **Redirection Symbols**: There are three redirection symbols as follows: - **>** : It prints the output of a command to file. ```bash ls > filename # this will add all files and folder to filename date > filename # this will change the content of the file to the date ``` - **>>** : It will append the output of a command to a file. ```bash ls >> filename # This will append the output of ls to file ``` - **|** : This is used to send the output of one command to another command. - ls | sort means first ls is executed and its output is send to sort then it will execute. ```bash ls | sort # this will print the files in sorted order ``` - #### Exercise - How to print the sorted list of users? who | sort - Count the number of files and directories in the current directory: ls | wc -l - Count the number of files and directories in directory user1/networks: ls user1/networks | wc -l - **grep** : print lines that match a given pattern. - Format: grep -options regex filename - Regex Basic Options: - `?` : The question mark indicates *zero or one* occurrences of the preceding element. For example, `colou?r` matches both "color" and "colour". - `*` : The asterisk indicates *zero or more* occurrences of the preceding element. For example, `ab*c` matches "ac", "abc", "abbc", "abbbc", and so on. - `+` : The plus sign indicates *one or more* occurrences of the preceding element. For example, `ab+c` matches "abc", "abbc", "abbbc", and so on, but not "ca". - `{n}` : The preceding item is matched exactly *n* times. - `{min,}` : The preceding item is matched *min* or more times. - `{min,max}` : The preceding item is matched at least *min* times, but not more than *max* times. - `.` : matches any single character. - `^` : Specify beginning. - `$` : Specify end. - [Read more about regex](https://en.wikipedia.org/wiki/Regular_expression) - Build Regex expression easily and visually with this tool - [Regex101](https://regex101.com/) - Options for grep - -v : print all lines that exludes the given regex. - -n : print line numbers. - #### Exercise - Search for 'is' in a file ```bash grep 'is' filename ``` - Search for lines that don't include 'is' ```bash grep -v 'is' filename ``` - Check if user1 is logged in or not ```bash who | grep 'user1' ``` - Find how many times user1 has logged in ```bash who | grep 'user1' | wc -l ``` - Search all lines that end with 's'. ```bash grep 's$' filename ``` - See all filenames that begin with 'a' ```bash # Solution 1 with grep ls | grep '^a' # Solution 2 with ls ls a* ``` - See all empty lines in a file ```bash grep '^$' filename -n ``` - Find all email address in a file ```bash grep '.\+@.\+\..\+' email_files.txt ``` - Explanation .\\+ means any character 1 or more times @ means match @ character literally .\\+ means any character 1 or more times \\. means match the . character literally .\\+ means any character 1 or more times - **Shell Variables** : Shell variables are special variables used by the shell. - **$HOME** : Contains path of home directory - **$PATH** : Contains executable's directories separated by a colon : - To Define your own variables: ```bash variable_name="value" ``` ### Thanks For Reading 😊 If you found this article helpful, please like and share! Feedbacks are welcome in the comments. --- #### You may also like: - [The Mutable Default Argument Mess in Python](https://blog.yuvv.xyz/the-mutable-default-argument-mess-in-python) - [Modern C++ Features](https://blog.yuvv.xyz/modern-cpp-features) - [What Happens When You Run a Computer Program?](https://blog.yuvv.xyz/what-happens-when-you-run-a-computer-program) - [Comprehensions in Python: Explained](https://blog.yuvv.xyz/comprehensions-in-python-explained) Connect with me on [Twitter](https://twitter.com/yuvraajsj18), [GitHub](https://github.com/yuvraajsj18), and [LinkedIn](https://www.linkedin.com/in/yuvraajsj18/).