Basics linux commands

1. sudo - Stands for Super User Do. The sudo command allows you to run commands with the superuser privileges.

2. whoami - Displays currently logged-in user.

3. cat - File concatenation and printing are done using the cat command.

   cat <file-name> - displays the contents of the file.

   cat > <file-name> - creates a new file, allows to input content interactively and redirects inputted content to the created file (> redirection operator).

4. echo - displaying lines of text or string which are passed as arguments on the command line. Can be used to create a file or empty a file.

   echo "Hello" - prints Hello

   echo "Hello" > hello.txt - Creates a file hello.txt with Hello as content in it.

   echo "World" >> hello.txt - appends the content(World) to the file hello.txt

   echo > hello.txt - Empties the content from hello.txt file.

5. pwd - shows the present working directory (abbr. Print Working Directory).

6. mkdir - make directory.

   mkdir <dir> - creates the directory.

   mkdir -p /A/B/C/D - creates directories (/A/B/C/D) with its parent directories if it does not exists (-p parent).

7. ls - list files or directories

   ls -a - list all hidden files and directories

   ls -altrh - lists all files & folders along with hidden files in a formatted manner

   -a all

   -l long listing format

   -t sort by time, newest first

   -r reverse order while sorting

   -h --human-readable with -l and -s, print sizes like 1K 234M 2G etc.

8. touch - creates an empty file or updates timestamp of the existing file.

   touch <file-name> - creates a single empty file named <file-name>.

   touch -a <file-name> - change only the access time

   touch -m <file-name> - change only the modification time

9. stat - Display file or file system status. It will display file size and timestamp (access, modify, and change time)

10. head <file-name> - displays first 10 lines of the file by default.

    head -n 5 <file-name> - displays first 5 lines of the file (-n number).

    head -n -5 <file-name> - print all but the last 5 lines of the file.

11. tail <file-name> - displays last 10 lines of the file by default.

    tail -n 5 <file-name> OR tail -n -5 <file-name> - displays last 5 lines of the file (-n number).

    tail -n +5 <file-name> - print all lines starting from the line 5.

12. sort - The sort command sorts the contents of a file, in numeric or alphabetic order, and prints the results to standard output.

    -h, --human-numeric-sort compare human readable numbers (e.g., 2K 1G)

    -n, --numeric-sort compare according to string numerical value

    -r, --reverse reverse the result of comparisons

13. rm - remove command.

    rm <file-name> - removes the file.

    rm -d <dir-name> - removes empty directory .

    rm -r <dir-name> - removes files & directories recursively from a directory (-r, -R, --recursive remove directories and their contents recursively).

    rm -rf - force remove the files & directories recursively from a directory (-f force).

14. cp - copy command.

    cp <src-file/dir> <dest-file/dir> - copy the files and directories from source to destination.

    cp -rp <dir1> <dir2> - copy dir1 directory to dir2 directory recursively

    -r recursive

    -p same as --preserve=mode,ownership,timestamps

15. mv - move or rename command.

    mv <old-filename> <new-filename> - renames the file to new name.

    mv <filename> <dirname> - moves the file to the directory.