Usage: head [OPTION]... [FILE]...

默认输出前10行

当指定多个文件时，在输出前输出各个文件名

当没有指定文件或指定的文件是“-”说明读取标准输入

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 显示头部前多少字节，这里的K是单位的标示，具体的单位参考下面列表，当使用-K时显示除了尾部多少字节外的所有内容

  -n, --lines=[-]K         print the first K lines instead of the first ;

                             with the leading `-', print all but the last

                             K lines of each file显示头部的多少行，默认显示头部10行，例如-n -b代表显示除了尾部512行外的所有行

  -q, --quiet, --silent    never print headers giving file names当指定多个文件时，出现内容中不输出文件名

  -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 , kB , K , MB *, M *,

GB **, G **, and so on for T, P, E, Z, Y.

Usage: tail [OPTION]... [FILE]...

默认输出尾部10行

当指定多个文件时，默认在输出内容前显示文件名

当没有指定文件或者指定的文件是“-”时，读取标准输入

Mandatory arguments to long options are mandatory for short options too.对于长选项不可忽略的参数对应短选项也不可忽略

  -c, --bytes=K            output the last K bytes; alternatively, use -c +K显示尾部的字节数，当使用+k参数时表示从k字节开始显示到末尾，例如-c +1b 显示512字节开始到末尾的内容

                           to output bytes starting with the Kth of each file

  -f, --follow[={name|descriptor}]

                           output appended data as the file grows;

                           -f, --follow, and --follow=descriptor are

                           equivalent追加显示文件最新的内容

  -F                       same as --follow=name --retry等同于使用 -f filename --retry操作

  -n, --lines=K            output the last K lines, instead of the last ;默认显示输出尾部的10行，当使用+k参数时指从第K行开始显示到末尾，例如-n +6显示第6行到末尾的内容

                           or use -n +K to output lines starting with the Kth

      --max-unchanged-stats=N

                           with --follow=name, reopen a FILE which has not

                           changed size after N (default ) 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--指定进程id,可以结合-f参数一起使用，当指定的进程终止时显示也终止

  -q, --quiet, --silent    never output headers giving file names ###同时显示多个文件时不输出文件名

      --retry              keep trying to open a file even when it is or当连接的文件突然不可访问时尝试重新连接

                             becomes inaccessible; useful when following by

                             name, i.e., with --follow=name

  -s, --sleep-interval=N   with -f, sleep for approximately N seconds当使用-f参数时可以，使用-s显示间隔

                             (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

      --help     display this help and exit

      --version  output version information and exit

If 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 , kB , K , MB *, M *,

GB **, G **, and so on for T, P, E, Z, Y.

tail -f /tmp/orzdba_mysql.log 

tail -f /tmp/orzdba_mysql.log --pid=