Another parsing bash script output to variables

Question

I know this has been asked before, and I have looked at the previous posts, but can't seem to get what I am trying to do working.

I know it's really basic, so I'm hoping this will be easy for most people on SO.

I want to create a simple bash script that pings an address, and then inserts the ping output into a csv file (or rather, into a file, separated with commas).

The ping command would be

ping -D google.com

and the output looks like

PING google.com (74.125.239.103) 56(84) bytes of data.
[1393992465.052723] 64 bytes from nuq05s01-in-f7.1e100.net (74.125.239.103): icmp_req=1 ttl=55 time=2.66 ms

I want to insert epoch time, ttl, and time into a file, separated by commas. If it's easy enough, then it wouldn't hurt to convert to the epoch time to a date also, but this can be my next step in this simple project.

I figured out the command to convert epoch time to human format is

date -d @[epoch_time]

Side trivia - why do I need the @?

Side trivia answer: that's the way the people who wrote date decided to recognize an epoch time. You can also pass arguments such as date -d 'now + 21 days'. — Jonathan Leffler
– Jonathan Leffler, Commented Mar 5, 2014 at 4:28
The @ avoids an ambiguity with epoch offsets for certain dates in the second half of August 1970. — rici
– rici, Commented Mar 5, 2014 at 4:35

Jonathan Leffler · Accepted Answer · 2014-03-05 15:35:19Z

1

ping -D google.com | sed -n -e 2p -e 2q |
while read epoch b64 bytes from host ip icmp ttl time ms
do
    date=$(date -d @$(sed 's/[][]//g' <<< "$epoch"))
    ttl=$(sed 's/ttl=//' <<< "$ttl")
    time=$(sed 's/time=//' <<< "$time")
    echo "$date,$ttl,$time"
done >> file.csv

Clearly, you can extend the number of lines you analyze by adjusting the first sed command. You can probably do the editing within the loop with ${var/x/y} notation, but I don't think of doing that until I'm writing up at the end because I've spent longer working with shells where that wasn't an option than I have with bash. Are you sure you don't want the host or IP address information?

In the cold light of morning, there's an easy way to improve the code:

ping -D google.com | sed -n -e 2p -e 2q |
while read epoch b64 bytes from host ip icmp ttl time ms
do
    epoch=${epoch#[}
    epoch=${epoch%]}
    date=$(date -d @${epoch})
    echo "$date,${ttl#ttl=},${time#time=}"
done >> file.csv

It's a matter of choice whether you create the date variable or simply embed the $(date -d @${epoch}) directly in the echo argument.

edited Mar 5, 2014 at 15:35

answered Mar 5, 2014 at 4:38

Jonathan Leffler

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1 Comment

chopsuei3 Over a year ago

Thanks so much! I couldn't figure out how to use sed, awk, or grep, but I knew it could be done with each. I don't need the host information, it's just for monitoring our network. Thanks again!

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