What is ls, pwd, chmod, chown in shell?

ls - list directory contents

When we have to list the directory contents we use ls command. Some common flags used with ls are:

ls [flags] [File]

• -l: Use a long listing format, showing details such as permissions, owner, group, size, and date modified
• -a: Show hidden files, which are files that start with a dot (.)
• -h: Show sizes in human-readable format, for example, 1K, 20K, 80M instead of numbers in bytes
• -t: It sort all the files by modification time, the new modification comes first.
• -r: Reverse the order of the sort, for example, sort files by modification time, oldest first

pwd - prints the name of current or working directory

pwd

We use pwd command when we want to display the absolute path of the current working directory.

rm - remove files or directories

rm is used to delete files or directories. Be careful when using rm, as there is no trash bin or undo for deleted files.

rm [flags](optional) [File]

Some of the useful flags are:

• -f: Force removal, do not prompt for confirmation
• -r: Remove directories and their contents recursively

chmod - change file mode bits

When we have to change the permissions of any files and directories chmod command is used.

chmod [permission_elements] [filename/directoryname]

Some of the basic option we use with chmod for changing permissions are:

• u: User/owner permissions
• g: Group permissions
• o: Other (world) permissions
• +: Add permission
• -: Remove permission
• -R: Operate on files and directories recursively

we can also use decimal number ranging between 0-7 for each element of the permission.
The permission in decimal format are:

• 4 - read
• 2 - write
• 1 - execute
• 6 - read and write
• 5 - read and execute
• 3 - write and execute
• 0 - no permission

chown - change owner of the file and group

chown is used to change the owner and/or group of a file.

if we want to change the user ownership of given file/directory (root access needed)

chown [username] [filename/directory]

change both user and group:

chown [username:groupname] [filename/directory]

• -R: Operate on files and directories recursively