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为了从冗长的日志中查看最后的执行结果，可以利用tail显示指定文件的最后几n行。

1.tail基本用法

tail -n 5 example.txt>>>输出last 5last 4last 3last 2last 1

下面是tail 的帮助文档：

Usage: tail [OPTION]... [FILE]...Print the last 10 lines of each FILE to standard output.# 不加参数默认输出最后十行With more than one FILE, precede each with a header giving the file name.# 也可针对多个文件输出With no FILE, or when FILE is -, read standard input.Mandatory arguments to long options are mandatory for short options too.  -c, --bytes=[+]NUM       output the last NUM bytes; or use -c +NUM to output starting with byte NUM of each file  # 按比特输出  -f, --follow[={name|descriptor}]                            output appended data as the file grows; an absent option argument means 'descriptor'  -F                       same as --follow=name --retry  # 随文件增加显示  -n, --lines=[+]NUM       output the last NUM lines, instead of the last 10;                             or use -n +NUM to output starting with line NUM  # 最常使用的参数，输出最后n行。+n则表示输出开始n行      --max-unchanged-stats=N                           with --follow=name, reopen a FILE which has not                             changed size after N (default 5) iterations                             to 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 at                             least once every N seconds  -v, --verbose            always output headers giving file names  -z, --zero-terminated    line delimiter is NUL, not newline      --help     display this help and exit      --version  output version information and exitNUM 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, whichmeans that even if a tail'ed file is renamed, tail will continue to trackits end.  This default behavior is not desirable when you really want totrack the actual name of the file, not the file descriptor (e.g., logrotation).  Use --follow=name in that case.  That causes tail to track thenamed file in a way that accommodates renaming, removal and creation.GNU coreutils online help: 
   Report tail translation bugs to 
   Full documentation at: 
   
    or available locally via: info '(coreutils) tail invocation'
   

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