I have a bash file which is executed every 5 seconds, it goes like this:
#! /bin/sh curl -I http://192.168.100.16:4000/status >> /home/debian2/debian0_ping.txt
It pings to a server running in a neighbor Virtual Machine and records the curl response into the specified file “debian0_ping.txt”
but the recorded response looks like this:
HTTP/1.1 200 ok <--- First Ping X-Powered-By: Express Content-Tye: text/plain; charset=utf-8 Content-Length: 2 Etag: "/2-n009QiTIwXgNt...." Date: Tue, 17 Aug 2021 18:56:25 GMT Connection: keep-alive HTTP/1.1 200 ok <--- Second Ping X-Powered-By: Express Content-Tye: text/plain; charset=utf-8 Content-Length: 2 Etag: "/2-n009QiTIwXgNt...." Date: Tue, 17 Aug 2021 18:56:28 GMT Connection: keep-alive
Which is a problem because I need the pings responses to be recorded this way (the most recent on top):
HTTP/1.1 200 ok <--- Second Ping X-Powered-By: Express Content-Tye: text/plain; charset=utf-8 Content-Length: 2 Etag: "/2-n009QiTIwXgNt...." Date: Tue, 17 Aug 2021 18:56:28 GMT Connection: keep-alive HTTP/1.1 200 ok <--- First Ping X-Powered-By: Express Content-Tye: text/plain; charset=utf-8 Content-Length: 2 Etag: "/2-n009QiTIwXgNt...." Date: Tue, 17 Aug 2021 18:56:25 GMT Connection: keep-alive
Finally I need to record only the first line (HTTP/1.1 200 ok) and the date line (Date: …) I’ve tried using SED commands, but it doesn’t seems to take variables as parameters to append onto the file.
Please, how can I achieve this, I know it’s simple but I’m too new at automating things.
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Answer
There is no straight-forward way to do reverse the output in bash.
To limit what lines you’re getting you can use the pattern grep 'pattern1|pattern2'.
You can do something like this to get the output in the desired format. NOTE: the output file must exist before running this.
curl -I https://www.google.com | grep 'HTTP|Date' | cat - /tmp/blah.txt > temp && mv temp /tmp/blah.txt
Output
HTTP/2 200
date: Tue, 17 Aug 2021 20:38:10 GMT
HTTP/2 200
date: Tue, 17 Aug 2021 20:38:07 GMT
HTTP/2 200
date: Tue, 17 Aug 2021 20:38:05 GMT
HTTP/2 200
date: Tue, 17 Aug 2021 20:38:03 GMT