Most standard tools are non-interactive (use switches and parameters rather than confirming details of operations with user). Some switches are interchangeable, some are mutually exclusive.

pwd

Prints path to current working directory

Switch	Shortcut	Description
--logical	-L	Use PWD from env
--physical	-P	Avoid symlinks

ls

Lists files and directories

Command	Description	Notes
ls	Shows files and directories in current directory
ls -l	Shows files and directories in current directory as a list
ls -h	Shows files and directories in current directory with sizes in human-readable format

df

Reports file system disk space usage

Command	Description	Notes
df	Disk space usage
df -h	Disk space usage in human-readable format	Human-friendly refers to using KB/MB/GB/TB units
df -i	inode usage	Programs can't write to filesystem without free inodes
df -T	Disk space usage with file system type
df -a	Include all filesystems, even inaccessible ones

du

Reports file system disk usage

Command	Description	Notes
du	Disk usage at specific path
du -c	Disk space at specific path - count sums for directories
du -h	Disk space at specific path - display output in human-friendly format	For example, KB/MB/GB/TB
du -s	Disk space sum at specific path

cp

Copies files/directories

Command	Description	Notes
cp input output	Copy file input to output
cp -r input output	Recursively copy files from input to output	This switch is commonly used to copy all subdirectories and files within

mv

Moves/renames files/directories

Command	Description	Notes
mv input output	Move file input to output	Moving one file onto another, existing one will overwrite it

rm

Removes files/directories

Command	Description	Notes
rm file	Removes file	❗ This is irreversible (without data recovery effort)
rm -r path	Removes files recursively in path	❗ Any rm -r command can quickly erase all data on computer. Certain devices might be even broken using this

grep

Searches for string in file(s)

Command	Description	Notes
grep string *	Find string in files in current directory
grep -r string *	Find string in files in current directory or its subdirectories
grep -n string *	Find string in files in current directory and display line number
grep -w string *	Find whole-word string in files in current directory
grep -e string *	Find regular expression string in files in current directory

chown

changes file owner and group

Command	Description	Notes
chown user file	Change file owner to user
chown user:group file	Change file owner to user and group to group
sudo chown -R user directory	Change directory owner to user for directory and its subdirectories

chmod

changes file permissions

Permissions are typically noted by 3 numbers; leftmost being user, middle being group and rightmost being others.

Number on each position is a sum of desired permissions: 4 (read), 2 (write) and 1 (execute).

Note that directories require execution permission to be opened!

Command	Description	Notes
chmod +x file	Make file executable
chmod 600 file	Change file permissions to 600 (owner only read/write)
chmod -R 600 directory	Recursively change files permissions	Caution: this will alter directory permission too - directories cannot be opened without executable permission

find

Searches for files or directories

Command	Description	Notes
find -name "*string*" -type f	Search for file with string in name
find -name "*string*" -type d	Search for directories with string in name

sudo

Allows executing other commands as root. Operating as root is considered a bad practice and can lead to system instability - even without any mistakes!

Command	Description	Notes
sudo	Shows sudo usage
sudo cmd	Executes cmd as root	❗ Linux allows you to instantly delete/break stuff. Any command ran as root (prefaced with sudo) can have grave consequences
sudo -u user_name cmd	Executes cmd as user named user_name