NAME
head - 输出文件开头的部分
SYNOPSIS
head [OPTION]... [FILE]...
DESCRIPTION
Print the first 10 lines of each FILE to standard output. With more
than one FILE, precede each with a header giving the file name.当不止要显示一个文件的时候，会在显示的每个文件前面显示文件名，例如==> filename <==
With no FILE, or when FILE is -, read standard input.当后面没有指定文件名或者是－的时候，从标准输入读入数据显示
Mandatory arguments to long options are mandatory for short options
too.较长的选项的命令参数对于较短的选项也是命令的
-c, --bytes=[-]N字符
print the first N bytes of each file; with the leading ‘-’,
print all but the last N bytes of each file
-n, --lines=[-]N行
print the first N lines instead of the first 10; with the lead‐\n ing ‘-’, print all but the last N lines of each file
-q, --quiet, --silent当显示多个文件的时候不列出文件名
never print headers giving file names
-v, --verbose
always print headers giving file names
--help display this help and exit
--version
output version information and exit
N may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000*1000, M
1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E,
Z, Y.在N后面可以跟后缀的，也就是单位了，例如head -c4b filename就是列出filename的头4b长度的字符