Grep examples

want to display lines starting with the string "root"
grep ^root /etc/passwd
root:x:0:0:root:/root:/bin/bash

Pattern	What does it match?
bag	The string bag.
^bag	bag at beginning of line.
bag$	bag at end of line.
^bag$	bag as the only word on line.
[Bb]ag	Bag or bag.
b[aeiou]g	Second letter is a vowel.
b[^aeiou]g	Second letter is a consonant (or uppercase or symbol).
b.g	Second letter is any character.
^...$	Any line containing exactly three characters.
^\.	Any line that begins with a dot.
^\.[a-z][a-z]	Same, followed by two lowercase letters (e.g., troff requests).
^\.[a-z]\{2\}	Same as previous, grep or sed only.
^[^.]	Any line that doesn't begin with a dot.
bugs*	bug, bugs, bugss, etc.
"word"	A word in quotes.
"*word"*	A word, with or without quotes.
[A-Z][A-Z]*	One or more uppercase letters.
[A-Z]+	Same, egrep or awk only.
[A-Z].*	An uppercase letter, followed by zero or more characters.
[A-Z]*	Zero or more uppercase letters.
[a-zA-Z]	Any letter.
[^0-9A-Za-z]	Any symbol (not a letter or a number).			a^c