grab 介绍
使用方法：
-O -- print file offset of match -l -- do not print the matching line (Useful if you want to see _all_ offsets; if you also print the line, only the first match in the line counts) -I -- enable highlighting of matches -c <n> -- Use n cores in parallel (useless and even slower in most situations) n <= 1 uses single-core -r -- recurse on directory -R -- same as -r