# CLI Commands

Command line interface is used to interact with the system for giving the commands in to a terminal.

**1.man :** man command is used to give manual pages for various commands .

```bash
man [option] keyword
```

\-k : Search for keywords in manual page names and descriptions.

\-f: Display a concise description of the specified topics.

\-a : Display all matching manual pages.

**2.pwd :** present working directory

```bash
pwd #pwd command is used to dispaly the present working directory.
```

**3.cd :** Change directory used to change the current directory

```bash
cd . #it represents the current directory
cd ~ #it moves to the home directory
cd / #it is used to change the current directory to root directory of file system
```

**4.mkdir :** mkdir is used to create a new directory.

```bash
mkdir dir_name
```

**5.mv :** mv is used to move the directory or file one place to another and used to rename.

```bash
mv path/to/source path/to/destination #moves the directory
mv filename newfilename #changes the file name
```

**6.ls :** ls command is used to list files and directories in a directory.

```bash
ls -l #use a long listing formate
ls -a #includes the hidden files and directories
ls -h #show file sizes in human-readable format (e.g., KB, MB).
ls -r #reverse the order of listing.
ls -t #sort by modification time, newest first.
```

**7.cp :** cp will copies the date from one file or directory in to another.

```bash
cp source_fname destination_fname #Copy a file to another location if 
cp -r directory/ /path/to/destination/ #Copy a directory and its contents recursively
```

**8.rm :** rm is used to remove the file and non empty directories.

```bash
rm f_name #delete the file.
rm -r dir_name #deletes the non empty directory.
```

**9.chmod :** chmod is used to change the permissions of a file and directories for read(4),write(2),execute(1).

```bash
chmod u+r f_name #giving user to read permission
#before:pooja@pooja-IdeaPad-3-15ITL05:~$ ls -l f2.txt
#--w-rw-r-- 1 pooja pooja 24 Apr 24 11:33 f2.txt
#after:pooja@pooja-IdeaPad-3-15ITL05:~$ chmod u+r f2.txt
#pooja@pooja-IdeaPad-3-15ITL05:~$ ls -l f2.txt
#-rw-rw-r-- 1 pooja pooja 24 Apr 24 11:33 f2.txt
#here - :file, rw-:user perimission -rw :group permission  -r-:other
chmod 777 dir_name or file_name #Giving permission read,write and execute to every one user,group,others
```

**10.chown :** chown is used to change the owner and/or group of files and directories.

```bash
sudo chown newuser:newgroup file.txt #Change both owner and group of a file:
#eg:pooja@pooja-IdeaPad-3-15ITL05:~$ chown user2:user2 f2.txt
sudo chown newuser:olduser file.txt
#pooja@pooja-IdeaPad-3-15ITL05:~$ ls -l f2.txt
#-rw-rw-r-- 1 pooja pooja 24 Apr 24 11:33 f2.txt
#pooja@pooja-IdeaPad-3-15ITL05:~$ sudo chown user2:pooja f2.txt
#[sudo] password for pooja: 
#pooja@pooja-IdeaPad-3-15ITL05:~$ ls -l f2.txt
#-rw-rw-r-- 1 user2 pooja 24 Apr 24 11:33 f2.txt
```

**11.sudo : i**t allows user to run command previleges.

```bash
sudo
```

**12.apt :** it is used to handle the package in linux.

```bash
sudo apt install
```

**13.touch :** it is used to create the file.

```bash
touch filename
```

**14.cat :** it is used to view the content of the file and copy the content of files in another using output redirection.

```bash
cat filename
cat f1_name f2_name >f3_name
```

**15.less :** it view the content of file page by page.

```bash
less filename
```

**16.more :** it view the text file line by line .

```bash
more filename
```

**17.tail :** it is used to give the last lines of the text file.

```bash
tail -n 4 filename
```

**18.grep :** it is used to search the matching pattern in file.

```bash
grep [option] pattern filename
```

**19.find :** it is used to find out the files or directory and certain pattern in filenames in directory.

```bash
find . -type f -name '*.txt' #it uses the files with .txt extension in cureent directory
find . -name 'fname' #it gives the fname file in current directory
```

**20.sort :** it is used to sort the content of the file.

```bash
sort filename
sort -r filename #sorts in reverse order
sort -u filename #removes the duplicates lines
```

**21.tree:** its shows the directories and files as tree structure based on their parents.

```bash
tree directoryname
```

### **OS/Process Related Commands**

**22.ps:** process status provides information about the processes currently running on the system.

```bash
ps aux #it gives all process in detailed
ps -u "username" #it gives the all process of user
ps -o pid,ppid,pgid,sid #it gives current running process in terminal
ps -ef #it gives currently running processes in system
```

**23.top :** it is used to display a dynamic, real-time view of system resource usage. It provides a continually updated display of information about processes and system performance.

```bash
top
```

**24.df :** it is used to display the disk space.

```bash
df -h #gives the disk space usage in human readable
```

**25.uname:** it is used to display the os name.

```bash
uname
```

**26.free :** Used to check for memory usage and available memory.

```bash
free
```

**27.lspci :** it gives information about the audio drivers.

```bash
lspci
```

**28.kill :** Used to kill the running process.

```bash
kill <pid>
```

### **Network Related Commands**

**29.ping :** it is used to test the network connection in server.

```bash
ping www.google.com
```

**30.ifconfig :** it is used to display detailed information about network interface and local ip.

```bash
curl ifconfig.me
```

**31.ssh :** it is used to securely connect to a remote system or server over a network. It stands for "Secure Shell" and is a standard method for remote login and secure communication between machines.

```bash
ssh username@hostname
```

### Bash Realated Commands:

**32.xargs :** it takes the output of one command and gives as input.

```bash
touch "file1 file2 file3" | xargs ls -l
```

**33.nano :** it opens the nano editor.

```bash
nano filename
```

**34.awk :** it is used to print the specific columns and the matching pattern.

```bash
awk '{ print $1, $3 }' fname.txt
```

**35.sed :** it is used for the substitute.

```bash
sed 's/a/h/g' fname #it substitute the a with h character
```

**36.Pipe operator :** it is used to connect the output of one command to the input of another command.

```bash
cat fname | grep "a" #cat reads the file and grep find a in file
```