grep,awk和sed

commons:
　　all of them could use regular-expression to match the result.

differences:
　　1)grep:
　　　　search for files with patterns.
　　2)awk:
　　　　anylyst for 'fields'; add addition message.
　　3)sed:
　　　　focus on lines of a file,including 'append,insert,delete',or even a range of lines.