I am not sure if this is even possible. But I am using this command to get network throughput.
ifstat -t -S -i wlan0
Run just like that it updates inline on the console but when I pipe it, it appends a new line to the file.
ifstat -t -S -i wlan0 >> /tmp/transfer.txt
Time wlan0
HH:MM:SS KB/s in KB/s out
21:33:35 4.27 201.47
21:33:36 4.20 178.88
21:33:37 4.41 190.76
21:33:38 4.32 186.61
21:33:39 5.07 177.42
21:33:40 4.15 182.87
21:33:41 5.70 180.93
21:33:42 4.21 194.71
21:33:43 3.80 181.35
21:33:44 3.86 185.57
21:33:45 3.92 189.78
21:33:46 4.08 195.29
etc...
OK I understand using this will overwrite the file.But only after I run it the first time.Not DURING the execution of the app.
ifstat -t -S -i wlan0 >> /tmp/transfer.txt
I really do not need to keep a log of all the transfer rates and only interested in writing that one line on every update while the application is running. Instead of appending lines during executions, I want it to create a new file or overwrite it every second.
Technically you're not piping, but redirecting output.
Looks like you want to use > instead of >>?
For obtaining just the last line while ifstat is executing you could extract it in a 2nd file like this:
while true; do tail -1 /tmp/transfer.txt > /tmp/transfer2.txt; sleep .5; done
To overwrite the file each time with out keeping a log.
while true; do ifstat -t -i wlan0 1 1 | tail -1 > /tmp/transfer.txt; sleep .5; done;