What is the command to view files in linux

Linux command to view files: 1. "cat", display the file content from the first line; 2. "tac", display from the last line; 3. "nl"; 4. "more" , display the file content page by page; 5. "less"; 6. "head", only look at the first few lines; 7. "tail", only look at the last few lines.

#The operating environment of this tutorial: Red Hat Enterprise Linux 6.1 system, Dell G3 computer.

Linux commands to view the contents of log files are

• cat displays the file contents starting from the first line
• tac displays the contents starting from the last line, It can be seen that tac is cat written backwards
• nl When displayed, the line number is output along the way!
• more Displays the file content page by page
• less is similar to more, but better than more, it can turn pages forward!
• head Only look at the first few lines
• tail only look at the tail lines

You can use man [command] to view each command Usage documentation, such as: man cp.

cat

Command function:

Display the file content starting from the first line

Command syntax:

cat [-AbEnTv]
一次显示整个文件。$ cat filename
2.从键盘创建一个文件。$ cat > filename 
只能创建新文件,不能编辑已有文件.
3.将几个文件合并为一个文件： $cat file1 file2 > file

Options and parameters

Related recommendations:《Linux Video Tutorial》

Check the contents of /etc/issue:

cat filename  #一次显示整个文件.
cat > filename  #从键盘创建一个文件。
#只能创建新文件,不能编辑已有文件.
cat file1 file2 > file   #将几个文件合并为一个文件

tac

Command function:

tac is just the opposite of the cat command. The file content is displayed from the last line. It can be seen that tac is cat written backwards!

Command syntax:

tac [选项]

Example

[root@www ~]# tac /etc/issue

Kernel \r on an \m
CentOS release 6.4 (Final)

nl

Command function:

Display line number; nl commandRead the file parameter (standard input by default), calculate the line number in the input, and write the calculated line number to the standard output . In the output, the nl command evaluates the lines to the left based on the flags you specify on the command line. Input text must be written in a logical page. Each logical page has header, body and footer sections (can have empty sections). Unless the -p option is used, the nl command resets the line number at the beginning of each logical page. The line calculation flag can be set individually for header, body, and footer sections (for example, header and footer lines can be counted but text lines cannot). The default result is a little different from cat -n. nl can do more display designs for line numbers, including the number of digits and whether to automatically complete 0s, etc.

Command syntax:

nl [-bnw] 文件

Options and parameters:

• -b: There are two main ways to specify the line number:
  • -b a: Indicates that the line number is also listed regardless of whether it is a blank line (similar to cat -n);
  • -b t: If there is a blank line, do not list the empty line Line number (default value);
• -n: Lists the ways to represent line numbers. There are three main types:
  • -n ln: The line number is on the screen. Displayed at the far left;
  • -n rn: The line number is displayed at the far right of its own field without adding 0;
  • -n rz: The line number is displayed at the far right of its own field. Display on the right and add 0;
• -w: The number of digits occupied in the line number field.

Example: Use nl to list the contents of /etc/issue

[root@www ~]# nl /etc/issue
     1  CentOS release 6.4 (Final)
     2  Kernel \r on an \m

more

Command function:

Flip page by page,more command is a text filter based on the vi editor. It displays the content of the text file page by page in full screen mode and supports keywords in vi Positioning operations. There are several shortcut keys built into the more list, the commonly used ones are H (get help information), Enter (scroll down one line), Space (scroll down one screen), Q (exit command).

Command syntax:

more(语法)(参数)

Options

实例

[root@www ~]# more /etc/man.config
#
# Generated automatically from man.conf.in by the
# configure script.
#
# man.conf from man-1.6d
....(中间省略)....
--More--(28%)  <== 重点在这一行喔！你的光标也会在这里等待你的命令

在 more 这个程序的运行过程中，你有几个按键可以按的：

• 空白键 (space)：代表向下翻一页；
• Enter ：代表向下翻『一行』；
• /字串 ：代表在这个显示的内容当中，向下搜寻『字串』这个关键字；
• :f ：立刻显示出档名以及目前显示的行数；
• q ：代表立刻离开 more ，不再显示该文件内容。
• b 或 [ctrl]-b ：代表往回翻页，不过这动作只对文件有用，对管线无用。

less

命令功能：

less命令允许用户向前或向后浏览文件，而more命令只能向前浏览。用less命令显示文件时，用PageUp键向上翻页，用PageDown键向下翻页。要退出less程序，应按Q键。

命令语法：

less(选项)(参数)

选项

实验

一页一页翻动，以下实例输出/etc/man.config文件的内容：

[root@www ~]# less /etc/man.config
#
# Generated automatically from man.conf.in by the
# configure script.
#
# man.conf from man-1.6d
....(中间省略)....
:   <== 这里可以等待你输入命令！

less运行时可以输入的命令有：

• 空白键 ：向下翻动一页；
• [pagedown]：向下翻动一页；
• [pageup] ：向上翻动一页；
• /字串 ：向下搜寻『字串』的功能；
• ?字串 ：向上搜寻『字串』的功能；
• n ：重复前一个搜寻 (与 / 或 ? 有关！)
• N ：反向的重复前一个搜寻 (与 / 或 ? 有关！)
• q ：离开 less 这个程序；

head

命令功能：

head命令用于显示文件的开头的内容。在默认情况下，head命令显示文件的头10行内容。

命令语法：

head [-n number] 文件

选项与参数：

例子

• -n ：后面接数字，代表显示几行的意思

[root@www ~]# head /etc/man.config

默认的情况中，显示前面 10 行！若要显示前 20 行，就得要这样：

[root@www ~]# head -n 20 /etc/man.config

tail

命令功能：

取出文件后面几行,tail命令用于输入文件中的尾部内容。tail命令默认在屏幕上显示指定文件的末尾10行。如果给定的文件不止一个，则在显示的每个文件前面加一个文件名标题。如果没有指定文件或者文件名为“-”，则读取标准输入。

命令语法：

语法：

tail [-n number] 文件

选项与参数：

• -n ：后面接数字，代表显示几行的意思
• -f ：表示持续侦测后面所接的档名，要等到按下[ctrl]-c才会结束tail的侦测

[root@www ~]# tail /etc/man.config
# 默认的情况中，显示最后的十行！若要显示最后的 20 行，就得要这样：
[root@www ~]# tail -n 20 /etc/man.config

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