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问题[head](unix)

Martin Hope
John Smith
Asked: 2021-09-28 06:21:52 +0800 CST
  • 0

似乎 几个月前我已经手动从我的头部移除了。/usr/bin/现在我有机会需要它，我没有它。如何在不重新安装整个发行版的情况下重新安装它？我的环境：Ubuntu 20.04 LTS 桌面。

ubuntu head
Martin Hope
Rick T
Asked: 2019-12-12 10:22:09 +0800 CST
  • 0

我正在尝试将文件中的前 5 行存储在变量中url。但我得到一个错误

-n5: command not found

fn_all_urls存储文件的路径/home/urls.txt

我的线路是：

url=head -n5 ${fn_all_urls} #get first 5 lines in file
echo "$url"

我在 Ubuntu 18.04 64 位上使用 bash

bash head
Martin Hope
Felix Dombek
Asked: 2019-08-22 06:08:35 +0800 CST
  • 8

我目前正在使用

watch head -n 17 *

这有效，但也显示所有行到第 17 行。基本上，我只想显示以我当前的方法显示的每个文件的最后一行。我怎样才能做到这一点？

例子

为了举例，让我们减少行 nr。到 7. 所以：

示例文件：

1
2
3
4
5
6
7
8

这一行：

watch head -n 7 *

输出

1
2
3
4
5
6
7

我想要的地方：

7
bash head
Martin Hope
user306023
Asked: 2018-09-06 14:21:01 +0800 CST
  • 3

head -numhead -n num与而不是相同head -n -num（其中num是任何数字）

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'

head（在 Fedora 28 上） 的手册页：

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)
linux head
Martin Hope
Pedro A
Asked: 2018-09-06 07:57:18 +0800 CST
  • 2

我需要head -z一个脚本（题外话，但可以在这个问题中找到动机），但在我的 CoreOS 835.13.0 中我得到了head: invalid option -- 'z'.

完整head --help输出：

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=[-]K         print the first K bytes of each file;
                             with the leading '-', print all but the last
                             K bytes of each file
  -n, --lines=[-]K         print the first K lines instead of the first 10;
                             with the leading '-', print all but the last
                             K lines of each file
  -q, --quiet, --silent    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

K 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: <http://www.gnu.org/software/coreutils/>
Report head translation bugs to <http://translationproject.org/team/>
For complete documentation, run: info coreutils 'head invocation'

有趣的是，最后一行告诉我要运行info coreutils 'head invocation'，但我得到了info: command not found.

coreutils head