等待等待一个过程结束;Sleep的睡眠时间是一定的。

wait是BASH内置命令。来自man bash:

    wait [n ...]
        Wait  for each specified process and return its termination sta-
        tus.  Each n may be a process ID or a job  specification;  if  a
        job  spec  is  given,  all  processes in that job's pipeline are
        waited for.  If n is not given, all currently active child  pro-
        cesses  are  waited  for,  and  the return status is zero.  If n
        specifies a non-existent process or job, the  return  status  is
        127.   Otherwise,  the  return  status is the exit status of the
        last process or job waited for.

Sleep不是shell内置命令。它是一个延迟指定时间的实用程序。

sleep命令可以支持不同时间单位的等待。GNU coreutils 8.4男人睡眠说:

    SYNOPSIS
        sleep NUMBER[SUFFIX]...

    DESCRIPTION
        Pause for NUMBER seconds.  SUFFIX may be ‘s’ for seconds (the default),
        ‘m’ for minutes, ‘h’ for hours or ‘d’ for days.  Unlike most  implemen-
        tations  that require NUMBER be an integer, here NUMBER may be an arbi-
        trary floating point number.  Given two or more  arguments,  pause  for
        the amount of time specified by the sum of their values.

Sleep只是在给定的秒数内延迟shell。

Wait使shell等待给定的作业。例如:

workhard &
[1] 27408
workharder &
[2] 27409
wait %1 %2

延迟shell，直到两个子进程都完成