pv命令可以用来度量执行命令的具体信息：时间，进度等。可以是管道的过程进度对用户透明，可以监控长时间操作的执行情况。

pv参数详解

Usage: pv [OPTION] [FILE]…

Concatenate FILE(s), or standard input, to standard output,with monitoring.

-p, –progress

show progress bar

显示进度条(目测不是很准的样子==)(默认)

-t, –timer

show elapsed time

显示任务已经进行的时长(默认)

-e, –eta

show estimated time of arrival (completion)

显示剩余多长时间完成(默认，但好像并不能显示)

-r, –rate

show data transfer rate counter

显示当前传输速率(默认)

-a, –average-rate

show data transfer average rate counter

显示平均传输速率

-b, –bytes

show number of bytes transferred

-F, –format FORMAT

set output format to FORMAT

-n, –numeric

output percentages, not visual information

显示进度百分比

-q, –quiet

do not output any transfer information at all

不输出任何信息

-W, –wait

display nothing until first byte transferred

-s, –size SIZE

set estimated data size to SIZE bytes

-l, –line-mode

count lines instead of bytes

-i, –interval SEC

update every SEC seconds

-w, –width WIDTH

assume terminal is WIDTH characters wide

-H, –height HEIGHT

assume terminal is HEIGHT rows high

-N, –name NAME

prefix visual information with NAME

-f, –force

output even if standard error is not a terminal

-c, –cursor

use cursor positioning escape sequences

L, –rate-limit RATE

limit transfer to RATE bytes per second

限制每秒的传输速率，RATE可为n,nK,nM,nG

-B, –buffer-size BYTES

use a buffer size of BYTES

-E, –skip-errors

skip read errors in input

-S, –stop-at-size

stop after –size bytes have been transferred

-R, –remote PID

update settings of process PID

-P, –pidfile FILE

save process ID in FILE

-h, –help

show this help and exit

-V, –version

show version information and exit

在默认情况下，pv命令会显示它能够计算出值的所有状态指标。例如，如果 pv 的输入不是文件，也没有手工指定大小，进度条会从左到右移动以表示有活动，但是由于没有总大小，它无法计算出已经完成的百分比。另外，pv命令可以限制硬盘的io速度。

需要注意的是：如果是对目录的操作，pv不能直接获得全部的大小。需要指定size或者计算目录大小。