unix - Grep examples - can't understand -

given following commands:

ls | grep ^b[^b]*b[^b]  ls | grep ^b[^b]*b[^b]* 

i know ^ marks start of line, can give me brief explanation these commands? do? (step step)

thanks!

^ can mean 2 things:

• mark beginning of line
• or negates character set (whithin [])

so, means:

• lines starting 'b'
• matching (0+) characters other 'b'
• matching 'b'
• followed not-'b' (or nothing @ all)

it match

bb bzzzzzb bzzzzzbzzzzzzz 

but not

zzzzbb bzzzzzxzzzzzz