head命令

head 與 tail 就像它的名字一樣的淺顯易懂，它是用來顯示開頭或結尾某個數量的文字區塊，head 用來顯示檔案的開頭至標準輸出中，而 tail 想當然爾就是看檔案的結尾。

1．命令格式

head [引數]... [檔案]...

2．命令功能

head 用來顯示檔案的開頭至標準輸出中，預設head命令列印其相應檔案的開頭10行。

3．命令引數

• -q 隱藏檔案名
• -v 顯示檔案名
• -c<位元組> 顯示位元組數
• -n<行數> 顯示的行數

4．使用範例

範例1：顯示檔案的前n行

命令：

head -n 5 log.log

演示操作及輸出：

[yiibai@localhost test]$ cat log.log
this is line 1.
this is line 2.
this is line 3.
this is line 4.

this is line5.

this is line 6.
this is line 7.
this is line 8.
this is line 9.
this is line 10.
this is line 11.
this is line 12.
this is line 13.
this is line 14.
this is line 15.
this is line 16.
this is line 17.
this is line 18.
this is line 19.
this is line 20.
this is line 21.
this is line 22.

-----------------end
[yiibai@localhost test]$ head -n 5 log.log
this is line 1.
this is line 2.
this is line 3.
this is line 4.

[yiibai@localhost test]$

範例2：顯示檔案前n個位元組

命令：

head -c 20 log.log

演示操作及輸出：

[yiibai@localhost test]$ head -c 20 log.log
this is line 1.
this[yiibai@localhost test]$

範例3：檔案的除了最後n個位元組以外的內容

命令：

head -c -32 log.log

演示操作及輸出：

[yiibai@localhost test]$ head -c -32 log.log
this is line 1.
this is line 2.
this is line 3.
this is line 4.

this is line5.

this is line 6.
this is line 7.
this is line 8.
this is line 9.
this is line 10.
this is line 11.
this is line 12.
this is line 13.
this is line 14.
this is line 15.
this is line 16.
this is line 17.
this is line 18.
this is line 19.
this is line 20.
this is line 21.
[yiibai@localhost test]$

範例4：輸出檔案除了最後n行的全部內容

命令：

head -n -6 log.log
```shell
演示操作及輸出：
```shell
[yiibai@localhost test]$ head -n -6 log.log
this is line 1.
this is line 2.
this is line 3.
this is line 4.

this is line5.

this is line 6.
this is line 7.
this is line 8.
this is line 9.
this is line 10.
this is line 11.
this is line 12.
this is line 13.
this is line 14.
this is line 15.
this is line 16.
this is line 17.
this is line 18.
[yiibai@localhost test]$