head tail[阮胜昌]

head显示文件前10行内容
head /etc/services
head -n 20 /etc/services   //显示前20行内容
  -c, --bytes=[-]N         print the first N bytes of each file;
                             with the leading `-', print all but the last
                             N bytes of each file
  -n, --lines=[-]N         print the first N lines instead of the first 10;
                             with the leading `-', print all but the last
                             N lines of each file
  -q, --quiet, --silent    never print headers giving file names
  -v, --verbose            always print headers giving file names
      --help     display this help and exit
      --version  output version information and exit

tail显示文件最后10行内容
tail /etc/services
tail -f /var/log/messages //时时显示文件内容,一般用于日志文件
[root@node203 ~]# tail -20 /etc/services  //显示最后20行内容

Mandatory arguments to long options are mandatory for short options too.
      --retry              keep trying to open a file even if it is
                           inaccessible when tail starts or if it becomes
                           inaccessible later; useful when following by name,
                           i.e., with --follow=name
  -c, --bytes=N            output the last N bytes
  -f, --follow[={name|descriptor}]
                           output appended data as the file grows;
                           -f, --follow, and --follow=descriptor are
                           equivalent
  -F                       same as --follow=name --retry
  -n, --lines=N            output the last N lines, instead of the last 10
      --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)
      --pid=PID            with -f, terminate after process ID, PID dies
  -q, --quiet, --silent    never output headers giving file names
  -s, --sleep-interval=S   with -f, sleep for approximately S seconds
                           (default 1.0) between iterations.
  -v, --verbose            always output headers giving file names
      --help     display this help and exit
      --version  output version information and exit