as root user: sudo su

File access

cat <file name> read
cat > <file name> overthrow

find <path> -name <name | regular expression > search by file name or regular expression
find <path> -name "*.txt" -delete delete all files matching regular expression

vi

vi <file name> open edit mode
:w save
:wq or zz save and exit
:q! exit without saving
i insert
d or <number>dd deletel lines
b to the beginning of the word
e to the end of the word
:u or :<number>u undo
:set nu show line number
:<line number> to the given line
<number>yy yank multiple lines from the cursor position