head -num与相同，head -n num而不是head -n -num（其中num有任何数字）
例子：
$ echo -e 'a\nb\nc\nd'|head -1
a
$ echo -e 'a\nb\nc\nd'|head -n 1
a
$ echo -e 'a\nb\nc\nd'|head -n -1
a
b
c
这head -1似乎没有记录在任何地方。
$ head --help
Usage: head [OPTION]... [FILE]...
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.
With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-c, --bytes=[-]NUM print the first NUM bytes of each file;
with the leading '-', print all but the last
NUM bytes of each file
-n, --lines=[-]NUM print the first NUM lines instead of the first 10;
with the leading '-', print all but the last
NUM lines of each file
-q, --quiet, --silent never print headers giving file names
-v, --verbose always print headers giving file names
-z, --zero-terminated line delimiter is NUL, not newline
--help display this help and exit
--version output version information and exit
NUM 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.
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation at: <https://www.gnu.org/software/coreutils/head>
or available locally via: info '(coreutils) head invocation'
手册页head（在Fedora 28上）：
HEAD(1) User Commands HEAD(1)
NAME
head - output the first part of files
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.
With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options
too.
-c, --bytes=[-]NUM
print the first NUM bytes of each file; with the leading '-',
print all but the last NUM bytes of each file
-n, --lines=[-]NUM
print the first NUM lines instead of the first 10; with the
leading '-', print all but the last NUM lines of each file
-q, --quiet, --silent
never print headers giving file names
-v, --verbose
always print headers giving file names
-z, --zero-terminated
line delimiter is NUL, not newline
--help display this help and exit
--version
output version information and exit
NUM 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.
AUTHOR
Written by David MacKenzie and Jim Meyering.
REPORTING BUGS
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report head translation bugs to <https://translationproject.org/team/>
COPYRIGHT
Copyright © 2017 Free Software Foundation, Inc. License GPLv3+: GNU
GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
tail(1)
Full documentation at: <https://www.gnu.org/software/coreutils/head>
or available locally via: info '(coreutils) head invocation'
GNU coreutils 8.29 December 2017 HEAD(1)
GNU的信息页面和在线手册head包含以下部分：
出于兼容性考虑，
head还支持过时的选项语法-[NUM][bkm][cqv]，只有先指定该语法才能识别该语法。
有观点认为，head -1相同head -n 1的是，破折号不是减号，但对于一个命令行选项标记。这是通常的习惯：以破折号开头的是控制处理方式的选项，命令行中的其他内容是文件名或要处理的其他实际目标。在这种情况下，它不是单字符选项，而是的简写形式-n，但基本上还是一个选项，而不是文件名。在head +1或中head 1，将以+1或1作为文件名。
双破折号--或--something也有不同的含义，就其本身（--）而言，它会停止选项处理，而在后面加上其他内容时，它会标记一个GNU风格的长选项。因此，head --1forhead -n -1不会符合该习俗。
如果我猜到了，我会假设存在一个古怪的捷径可以肯定，但不能否定，因为前一种情况更有用且更容易实现。（此外，该标准仅针对线的正值进行定义。）-n iiihead
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