Linux commands to know

ls command

The ls command is used in Linux and Unix-based operating systems to list files and directories in a directory. Here are some commonly used options with the ls command:

ls - to show content inside a directory
ls -a : list hidden files also with other files
ls -l : list content with long details
ls -R : also shows content available in sub directory

cd command

The cd command is used in Linux and Unix-based operating systems to change the current working directory. It allows you to navigate through the file system and access different directories.

cd: Without any arguments, the cd command takes you to your home directory.
cd <directory>: Changes the current directory to the specified directory. For example, cd Documents moves you to the "Documents" directory if it exists in the current directory.
cd ..: Moves up one level in the directory hierarchy. For example, if you're in the "Documents" directory, cd .. will take you back to the parent directory.
cd /: Takes you to the root directory.
cd ~: Takes you to your home directory.
cd -: Takes you to the previous directory you were in.

mkdir command

The mkdir command is used in Linux and Unix-based operating systems to create directories (folders). It allows you to create one or multiple directories at a time.

mkdir - to make directory
mkdir folder1/folder2 - creates folder 2 inside folder 1 if the folder 1 exists in current directory
mkdir -p folder1/folder2 - p flag to create parent directories as needed

cat command

The cat command is used in Linux and Unix-based operating systems to concatenate and display the contents of files. It is also frequently used to create new files or append to existing ones

cat name.txt - list all the things available in the text file
cat > Hello - creates a hello file and we can write content into it
cat file1.txt > file2.txt - copies the content of file 1 into file 2
cat file1.txt file2.txt - print file 1 then file 2
cat file1.txt | tr a-z A-Z > upper.txt - convert content of file 1 into uppercase using tr (translate) command and then saving into upper.txt

find command

The find command is used in Linux and Unix-based operating systems to search for files and directories within a specified directory hierarchy.

find . - find files in current directory
find . -type d - find the directories only inside current folder
find . -type f - find files only
find . -type f -name "two*" - find files that start with two ex - two.txt two.exe
find . -type f -iname "two*" - not case sensitive
find . -type f -mmin -20 - shows file modified less than 20 mins ago
find . -type f -mmin +15 - shows file modified more than 15 mins ago
find . -type f -mmin +2 --mmin -10 - modified more than 2 mins and less than 10 mins ago
-mtime - modified time in days
find . -type f -maxdepth 1 - max depth 1 means in current directory but not in sub-directory
find . -type f -size +1k - search by size
find . -perm 777 - find files by permission, 777 means read-write-executable

chmod command

Used to change permissions of file and directories

chmod u=rwx,g=rw,o=r uppertxt - change file permission to read,write,exec for user, read,write for group, and read for others
chmod 777 upper.txt - using octal numbers for read,write,execute for all three
chown - used to change ownership of files and directories
chown root upper.txt - error thrown as it requires sudo aslo
sudo chown root upper.txt - now the file upper.txt is only accesible to root user which is provided by sudo command.

Other commands

touch

touch text.txt - used to create files
touch folder3/hello.txt - create hello file inside folder3

cp

cp file.txt copyfile.txt - create a copy a file
cp -R folder1 folder2 - create copy of folder1 and entire subtree in folder2 and runs even if error occurs.

mv

mv name.txt random - moves name file into random named folder
mv file1.txt file2.txt - file1 was removed and file 2 was created

rm

rm copyfile.txt - permanently deletes/removes the file only
rm -R copiedFolder - R flag to specify to delete the folder

df

df - display info about the disk space usage in kb
df -m : m flag to display info in mb
df -g : to display in gb
df -h : to display in human-readable format

head

head - display first few lines of file
head file.txt - display few no of lines decided by system
head -n 4 file.txt - n flag to change the number of line to display to 4

Similarly we have tail command which just do the opposite of head command.

history

history - list history of commands we used
history | grep "ls" -list of ls commands we used
!2742 - id of one of our previous command, doing this will run this command from the history

zip

zip - to compress files and directories into a zip archive
zip files.zip companies.txt - zip companies file
unzip files.zip - to unzip files

useradd User - to add new user
passwd User - to set password
userdel User - deletes a user names User

Info

To know more about a particular command just write <command name> --help you will get more possible things that we can do using a command.

Operations -

& - creates a background on which some commands run so that others don't get blocked
&& - only when lhs in successful then only rhs will run
| - send output in first command in the second command
|| - if lhs get executed then it's print otherwise rhs will then run
! - not operator to reverse the logic output
rm -rf !(name.txt) - remove file except names.txt
\>> - used to append data not overwrite it
{} - combination operator used to group the commands

Best things to do with these commands is not to memorize them but play with them whenever you are dealing with terminal.

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