问题
I want to pipe the ping output with only its delay time to a text. while I do , I get this as expected
ping somesite
PING somesite (220.181.57.217) 56(84) bytes of data.
64 bytes from 220.181.57.217: icmp_seq=1 ttl=52 time=43.4 ms
64 bytes from 220.181.57.217: icmp_seq=2 ttl=52 time=43.7 ms
64 bytes from 220.181.57.217: icmp_seq=3 ttl=52 time=43.4 ms
Then I do this
ping somesite | awk -F '[:=]' '{print $5}'
43.3 ms
43.2 ms
43.3 ms
43.2 ms
43.2 ms
43.1 ms
43.1 ms
43.3 ms
43.2 ms
43.6 ms
43.3 ms
43.3 ms
So The first line is blank, then I figured I had to get rid of it first.
ping somesite | grep -v "PING" | awk -F '[:=]' '{print $5}'
But there isn't any output. When I do either
ping somesite | grep -v "PING"
or
ping somesite | awk -F '[:=]' '{print $5}'
It will work. When putting them together. It won't. I'd like to know the reason for this.
回答1:
You're not getting any output when piping with grep due to block buffering in grep command.
You can make grep use the line buffering so get the output for each line:
ping google.com | grep --line-buffered -v "PING" | awk -F '[:=]' '{print $5}'
However you don't need grep because you can do this using single awk:
ping google.com | awk -F '[:=]' 'NR>1{print $5}'
回答2:
With a small modification:
ping somesite | awk -F '[:=]' 'NR!=1 {print $5}'
回答3:
I've figured it out by the answer from https://askubuntu.com/questions/562344/what-does-grep-line-buffering-do
So pretty much grep buffers the output until 4096 bytes before sending the lines to awk. The grep option --line-buffered will solve my problem.
回答4:
Checking with NR (Number of records)actually remove first record from the output,
ping somesite | awk -F '[:=]' 'NR!=1 {print $5}'
or
ping somesite | awk -F '[:=]' 'NR>1 {print $5}'
You can check with NF (Number of fields) to filter any such record which doesn't fit in pattern,
ping somesite | awk -F '[:=]' 'NF==5 {print $5}'
来源：https://stackoverflow.com/questions/41162250/filter-ping-result-with-grep-and-awk-altogether-doesnt-work