reading the output from dd command

Question

I'm testing my network speed with a script and for it to calculate average speed I need to read the speed for each run.

command:

dd if=InputFile of=OutputFile bs=4096k

output:

64+0 records in
64+0 records out
268435456 bytes (268 MB) copied, 1.8519 s, 145MB/s

the problem is that the dd command always prints the output to stdout. I can manage to pipe it or write it to file so i can read the 145MB/s

I've tried the following lines:

dd if=InputFile of=OutputFile bs=4096k >> log.txt - creates an empty file and prints to stdout

dd if=InputFile of=OutputFile bs=4096k | grep * - fails

echo `dd if=InputFile of=OutputFile bs=4096k` # fails

`dd` writes its messages to standard error. So: `dd ... 2>> log.txt`. — gniourf_gniourf, Oct 25 '15 at 13:22

score 4 · Accepted Answer · answered Oct 25 '15 at 13:22

4

Your problem is that dd does not print that output to stdout, but to stderr.

You have to redirect using 2> ..., for example

dd if=/dev/zero of=/dev/null count=1 2> >( grep copied )

answered Oct 25 '15 at 13:22

dfogni

Or probably more like ...`| awk '/copied/ { print $1 }'` – tripleee Oct 25 '15 at 13:30

score 1 · Answer 2 · answered Oct 25 '15 at 13:31

1

You can also get the PID of the dd process and setup a watch to send a USR1 signal to your liking. Then redirect that to a file!!!!

answered Oct 25 '15 at 13:31

g24l

2 Answers2