Comprehensive Guide to Essential Shell Scripting Commands

This documentation serves as a comprehensive guide to essential shell scripting commands, providing step-by-step explanations and practical examples for each command.

ls: Lists directory contents.
- Explanation: The ls command is used to list the files and directories within a specified directory.
- Example:
```
   ls
```
  This command will list all the files and directories in the current directory.
pwd: Prints the current working directory.
- Explanation: pwd stands for "print working directory." It displays the full path of the current working directory.
- Example:
```
    pwd
```

Running this command will print the current directory's absolute path.

cd: Changes the current directory.
- Explanation: The cd command allows you to change the current working directory to the specified directory.
- Example:
```
    cd /path/to/directory
```
  This command will change the current directory to the one specified.
cd .. : Moves up one directory level in the directory tree.
- Explanation: cd .. allows you to move one level up in the directory structure.(It will go back from one folder)
- Example:
```
    cd ..
```
  Running this command will move you up one directory level.
cd ../..: Moves up two directory levels in the directory tree.
- Explanation: This command moves you up two levels in the directory structure.(It will go back from 2 folders)
- Example:
```
  cd ../..
```
  Running this command will move you up two directory levels.
cd folder1/folder2: Changes to a directory within the current directory.
- Explanation: You can change to a directory within the current directory by specifying its path.
- Example:
```
    cd documents/scripts
```
  This command will change the current directory to "scripts" within the "documents" directory.
ls -ltr: Lists files in long format sorted by modification time.
- Explanation: The -ltr option displays files in long format, sorted by modification time in reverse order.
- It provides the information about that file or folder along with timestamp
- if its starting with ‘d’ then it is directory or else file
- Example:
```
    ls -ltr
```
  Running this command will list files in long format sorted by modification time, with the newest files appearing last.
vi: Opens the vi text editor.
- Explanation: vi is a text editor used to create or edit files.
- Example:
```
    vi filename.txt
```
  This command will open the vi text editor and create/edit the file named "filename.txt".
cat: Concatenates and displays file content.
- Explanation: cat is used to display the contents of one or more files.
- Example:
```
    cat filename.txt
```
  This command will display the contents of the file named "filename.txt".
mkdir: Creates a new directory.
- Explanation: mkdir is used to create a new directory.
- Example:
```
    mkdir new_directory
```
rm filename: Removes a file.
- Explanation: rm is used to remove/delete a file.
- Example:
```
    rm file.txt
```
  This command will remove the file named "file.txt".
rm -r foldername: Removes a directory recursively.
- Explanation: rm -r is used to remove a directory and its contents recursively.
- Example:
```
    rm -r directory
```
  This command will remove the directory named "directory" and all its contents.
nproc: Prints the number of processing units available.
- Explanation: nproc displays the number of processing units (CPU cores) available on the system.
- Example:
```
    nproc
```
  This command will print the number of CPU cores available.
free -g: Displays the amount of free and used memory in gigabytes.
- Explanation: free -g shows the system's memory usage in gigabytes.
- Example:
```
    free -g
```
  This command will display memory usage in gigabytes.
df -h: Displays disk space usage in a human-readable format.
- Explanation: df -h shows disk space usage in a human-readable format.
- Example:
```
    df -h
```
  This command will display disk space usage in a human-readable format.
top: Displays real-time system information.
- Explanation: top provides real-time information about system processes, CPU usage, and memory usage.
- Example:
```
  top
```

This command will display real-time system information

chmod: Changes file permissions.
- Explanation: chmod is used to change the permissions of a file or directory.
- Example:
```
  chmod 755 filename.txt
```

This command will change the permissions of the file "filename.txt" to 755

stat -c %a filename: Displays file access rights in octal format.
- Explanation: stat -c %a displays file access rights in octal format.
- Example:
```
  stat -c %a filename.txt
```

This command will display the access rights of the file "filename.txt" in octal format.

man: Displays the manual of a command.
- Explanation: man displays the manual pages for a specified command.
- Example:
```
  man ls
```

This command will display the manual page for the ls command.

grep: Searches for patterns in files.
- Explanation: grep is a command-line utility for searching plain-text data sets for lines that match a regular expression.
- Example:
```
  grep "pattern" filename.txt
```

This command will search for lines containing the specified pattern in the file "filename.txt".

curl: Transfers data to or from a server.
- Explanation: curl is a command-line tool for transferring data with URL syntax. It supports various protocols including HTTP, HTTPS, FTP, etc.
- Using the curl command we can get the information from the api’s as well just like in python we are doing with the requests module
- Example:
```
  curl https://example.com
```

This command will retrieve the contents of the specified URL.

wget: Downloads files from the internet.
- Explanation: wget is a command-line utility for downloading files from the web using HTTP, HTTPS, or FTP protocols.
- Using Wget command it will download that information and save it in the logfile locally
- Example:
```
  wget https://example.com/file.txt
```
  This command will download the file "file.txt" from the specified URL.
pipe |: Redirects the output of one command as input to another.
- Explanation: The pipe (|) operator is used to redirect the output of one command as input to another command.
- Pipe parameter sends the output of the first command to the second command
- Pipe command it will receive the information from the stdout not from stdin
- Example:
```
  ls | grep "pattern"
```
  This command will list files in the current directory and then filter the output to display only the lines containing the specified pattern.
awk -F "" '{print $2}': Processes text files.
- Explanation: awk is a programming language used for pattern scanning and processing. -F "" specifies an empty field separator, and {print $2} prints the second field.
- Example:
```
  awk -F "," '{print $2}' file.txt
```
  This command will process the text file "file.txt" using comma as a field separator and print the second field of each line.
find / -name filename: Searches for files and directories.
- Explanation: find is a command-line utility for searching files and directories in a directory hierarchy. / specifies the starting directory, and -name filename specifies the search criteria.
- Example:
```
  find / -name "file.txt"
```
  This command will search for the file named "file.txt" starting from the root directory /.
shebang: Specifies the interpreter for a script.
- Explanation: The shebang (#!) line at the beginning of a script specifies the interpreter to be used to execute the script.
- Example:
```
  #!/bin/bash
```
  This shebang line specifies that the script should be executed using the Bash shell.
set -x: Enables tracing of commands and their arguments.
- Explanation: set -x enables debugging mode, where each executed command and its arguments are printed to the terminal.
- set -x : It will print all the commands on the script in a debug mode
- Example:
```
  set -x
```
  This command enables tracing of commands and their arguments.
set -e: Exits immediately if a command exits with a non-zero status.
- Explanation: set -e causes the script to exit immediately if any command returns a non-zero exit status.
- set -e : It will exit the script when there is an error in the script
- Example:
```
  set -e
```
  This command enables immediate exit on error.
set -o: Displays or sets shell options.
- Explanation: set -o displays or sets various shell options.
- We need to use set -o because set -e won’t give any error if the last command in the line is executed successfully. It will fail only if the last command on the line fails
- Example:
```
  set -o
```
  This command sets the nounset option, causing an error to occur if

Comprehensive Guide to Essential Shell Scripting Commands

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