记录：347

场景：在CentOS 7.9操作系统上，使用tail命令指定行数查看文件内容；使用tail查看文件实时输出内容。比如查看Tomcat的日志文件等。

版本：

操作系统：CentOS 7.9

1.命令应用

在/home/apps/work目录下，有文件intro.txt。

(1)指定行数查看内容

命令：tail -n 10 intro.txt

解析：tail -n 10，输出文件的最后10行内容。

(2)查看文件实时输出内容

命令：tail -f intro.txt

命令：tail -F intro.txt

解析：tail -f ，查看文件实时输出内容，比如查看Tomcat的catalina.out时，只要服务在运行，就可以实时打印服务运行日志。

(3)查看最近几秒的文件内容

命令：tail -s 10 intro.txt

解析：查看最近几秒的文件内容

(4)查看版本

命令：tail --version

解析：查看版本信息，本例：tail (GNU coreutils) 8.22。

(5)输出指定字节的内容

命令：tail -c 1024 intro.txt

解析：输出文件最后1024字节内容。

2.命令帮助手册

命令：tail --help

解析：查看tail支持全部命令和选项，在实际工作中，查看这个手册应该是必备之选。

Usage: tail [OPTION]... [FILE]...
Print the last 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            output the last K bytes; or use -c +K to outputbytes starting with the Kth of each file-f, --follow[={name|descriptor}]output appended data as the file grows;an absent option argument means 'descriptor'-F                       same as --follow=name --retry-n, --lines=K            output the last K lines, instead of the last 10;or use -n +K to output starting with the Kth--max-unchanged-stats=Nwith --follow=name, reopen a FILE which has notchanged size after N (default 5) iterationsto see if it has been unlinked or renamed(this is the usual case of rotated log files);with inotify, this option is rarely useful--pid=PID            with -f, terminate after process ID, PID dies-q, --quiet, --silent    never output headers giving file names--retry              keep trying to open a file if it is inaccessible-s, --sleep-interval=N   with -f, sleep for approximately N seconds(default 1.0) between iterations;with inotify and --pid=P, check process P atleast once every N seconds-v, --verbose            always output headers giving file names--help     display this help and exit--version  output version information and exitIf the first character of K (the number of bytes or lines) is a '+',
print beginning with the Kth item from the start of each file, otherwise,
print the last K items in the file.  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.With --follow (-f), tail defaults to following the file descriptor, which
means that even if a tail'ed file is renamed, tail will continue to track
its end.  This default behavior is not desirable when you really want to
track the actual name of the file, not the file descriptor (e.g., log
rotation).  Use --follow=name in that case.  That causes tail to track the
named file in a way that accommodates renaming, removal and creation.GNU coreutils online help: 
For complete documentation, run: info coreutils 'tail invocation'

以上，感谢。

2022年11月27日