emahtab / linux-for-me

Linux Cheatsheet

linux-for-me

Linux Cheatsheet

1. Creating a new directory in linux

   mkdir work
   
   

   Above command will give error if work directory already exist. If we use the p option with mkdir it will not give error even if the directory already exist

   mkdir -p work
   
   

2. Creating a new file or editing an existing file (using gedit editor)

   gedit index.html
   

3. Copying a file (index.html) from one directory (e.g. /home/bourne/work) to another (e.g. /home/bourne/Downloads)

   
   cp /home/bourne/work/index.html /home/bourne/Downloads
   
   

4. Changing the current directory to home directory (e.g. /home/bourne or /home/mahtab)

   cd ~
   

5. Changing current directories using ~ symbol

   cd ~/work
   cd ~/Downloads
   

6. Copying a directory (/home/bourne/work) to another directory (/home/bourne/Videos)

   cp -R /home/bourne/work /home/bourne/Videos/
   or
   cp -r /home/bourne/work /home/bourne/Videos/
   

7. Removing a file (e.g. /home/bourne/Videos/work/info.txt)

   rm /home/bourne/Videos/work/info.txt
   

8. Removing a directory ( e.g. /home/bourne/Videos/work ) recursively

   rm -r ~/Videos/work
   

9. Removing all the files in a directory (e.g. ~/codes/)

rm ~/codes/*

Note that above command will only delete all the files under codes directory but it won't delete any sub-directories under codes

10. Deleting files and sub-directories under a directory (e.g. /home/bourne/codes)

    rm -r ~/codes/*
    

11. Renaming a file (e.g. ~/codes/alpha.txt to ~/codes/awesome.txt)

    mv ~/codes/alpha.txt ~/codes/awesome.txt
    

12. Renaming a folder (e.g. ~/codes to ~/sourceCodes)

    mv ~/codes ~/sourceCodes
    

13. Counting the number of files in a directory

    ls -l | wc -l
    

    Note that above command will give the result one greater than the actual number of files

14. Clearing the terminal screen

    clear
    

Vi Editor Cheatsheet

**Opening a file in vi editor**

```
vi nameOfTheFile
```
**Closing an open file and Quiting the vi editor**

```
:q
```
**Saving and closing a file and quitting the editor**

```
:wq
```

**Switching from command mode to insert modes**
```
To switch from command mode to insert mode use 'i'. To switch from insert mode to command mode use 'esc' key
```

**Editing a file**
```
To edit a file in vi ceditor first switch to insertion mode ( by pressing esc and then i), once you are in insertion mode
you can edit the file
```

**Deleting characters**
```
To delete a single character use 'x' in command mode and to delete a complete line use 'dd' in command mode  
```

**Moving in lines up and down, right and left**
```
To move between lines up and down use arrow keys in command mode. To move left and right use left and right arror keys in command mode 
```

Grep Command

Searching for a string in a file

grep CGHR someText.txt

Case Insensitive Search with Grep

grep -i cghr someText.txt

Printing the line numbers in the output result

grep -ni cghr someText.txt

Seraching for a string with multiple words

grep -ni "quote is must" grep101/someText.txt

Searching in multiple files

grep -in grunt grep101/someText.txt grep101/otherText.txt

Searching for a pattern recursively in all the files under a directory

grep -inr grunt grep101

Coloring the matched string

grep -r --color mahtab .

Git grep

If you are working with a gir repository then git grep ignores all the files and directories defined in .gitignore file

git grep mahtab .

Getting context around grep matches

A = after, B = before, C = both after and before

grep --color -rn -C 2 mahtab .

Using special characters . and * with grep

. means any character and * means zero or more occurances

grep --color -rn "(http.*)" .

grep escaping the special characters

If you want special characters to be treated as normal characters you can escape it with \

grep -nr "www\." . .

grep extended reguluar expressions

by default grep treats . and * as special characters, grep also supports extended regular expressions +(one or more) and ?(zero or one) symbols. To use it either you can use the -E option with grep or escape these characters with backslash() to be treated as special characters

grep -nr -E "https?" .

or

grep -nr "https\?" .

grep looking for multiple patterns using or expression (|)

We can specify multiple patterns using to look for using |, note that using -E option is mandatory to use |

grep -nriE "chaaye|chai" .


grep -nriE "chaaye|chai|mahtab" .

grep matching only at line begining(^) or at end($) using anchor characters

^ will match the pattern only if it is at the begining of line, similarly $ will only match the pattern if it is at the end of the line

grep -rn "^I" .

  
grep -rni "bangalore$" .

grep using bracket expressions and character classes

We can bracket expressions [a-z], [A-Z], [0-9] and also character classes [:alpha:], [:digit:], [:alnum:], [:xdigit:] with grep

find views/ -name "*ejs" | grep "[0-9]"

or

find views/ -name "*ejs" | grep "[[:digit:]]"

grep grouping our search string with parantheses

We can group our search patterns to create a precise search pattern that we want to search, note that while using parantheses you will also have to use -E option. Both of below queries will give same result

find views/ -name "*ejs" | grep "/[a-z]*-[a-z]*-[a-z]*\.ejs"

or

find views/ -name "*ejs" | grep -E "/([a-z]*)-([a-z]*)-([a-z]*)\.ejs"

Inverting a grep search

We can invert the grep search with -v option, so grep will list what that doesn't match rather than what does match

ls -l | grep -v "node_modules"

find views/ -name "*.ejs" | grep -v "blog"

Find command

find command is used for searching for files

Searching for specific file

find -name cme-esb.xml

By default find will look for file under current directory and sub-directories

Searching all ejs files inside views directory

find views -name "*ejs"

Combining find and grep together with xargs

find views/ -name "*ejs" | xargs grep -in "bangalore"

Shortcut for opening a terminal

If you are on a Ubuntu machine you can open a new terminal by pressing the keys Ctrl+Alt+t but this shortcut does not work in Debian so you have to set this shortcut manually to open the terminal using Ctrl+Alt+t

To find out what version of Linux (distro) you are running

You can use the below command to find out which version of linux you are running

cat /etc/*-release

scp (secure copy)

To copy a directory from your local machine to remote server's /var/www/html/ directory

scp -r mansa2 [email protected]:/var/www/html/

To copy a file from remote server to your local machine

scp [email protected]:/var/www/data/abc.wav /home/mahtab/recordings/

#chown (changing ownership) To change owner and group owner to root for all the files and sub directoies within a directory use below command

sudo chown -R root:root mansa2

#chmod (changing permissions) To change permissions for a folder

sudo chmod 755 mansa2

To change permission for all the files under a directory

sudo chmod 644 mansa2/*

Note that above command will not change file permissions for sub directories and files inside sub directories

Zipping a directory

 zip -r name-of-the-zip-to-be-created.zip dir

Zipping a single file

  zip name-of-the-zip-to-be-created.zip file

Using tar to compress a dir into a .tgz file

 tar -czf compressed-file-name.tgz dir

Using tar to list files inside .tgz file

 tar -tzf compressed-file-name.tgz

Using tar to uncompress a .tgz file

tar -xzf compressed-file-name.tgz

Command Substitution

https://docs.google.com/document/d/1ciIjphq_icU9iqpYdF6CW2Yf9HDyF7IHmzZUrP6mZ90/edit?usp=sharing