mkdir dir	create single directory dir
mkdir dir1 dir2	create multiple directories dir1 dir2
mkdir -p dir/a/b/c	create nested directory dir/a/b/c
mkdir dir{1..10}	created 10 numbered directories from dir1 to dir10
rm -r dir	remove dir recursively
touch file	create empty file file
touch file1 file2	create multiple files file1 file2
touch file{1..10}	create 10 numbered files from file1 to file10
cp -rf /dir/file1 /dir2	copy file file1 to dir2 directory recursively and forcefully
mv /dir/file1 /dir2	move file file1 to dir2 directory
rm file1	remove file file1
ls -al	show files - both regular & hidden files and their permissions
cat file1	display contents of file1
find /dir1 -name file1	find file1 under /dir1 directory
find /dir1 -perm 664	find all files/directories with read, write permission to owner and group, read permission for others in directory dir1
find /dir1 -empty -exec rm -r {}**	find and remove all empty files/directories from /dir1
wc -l file1	count the number of lines in file1
wc -w file1	count the number of words in "file1*
head file1	display top 10 lines of file1
head -n 20 file1	display top 20 lines of file1
tail file1	display last 10 lines of file1
tail -n 20 file1	display last 20 lines of file1

Calculate permission digits by adding numbers below
4	read (r)
2	write (w)
1	execute (x)

File Permission Numbers