How to evaluate http response codes from bash shell script

Question

I have the feeling that I m missing the obvious  but have not succeeded with man  curl wget  or google   http  makes such a bad search term   I m looking for a quick amp dirty fix to one of our webservers that frequently fails  returning status code 500 with an error message  Once this happens  it needs to be restarted   As the root cause seems to be hard to find  we re aiming for a quick fix  hoping that it will be enough to bridge the time until we can really fix it  the service doesn t need high availability   The proposed solution is to create a cron job that runs every 5 minutes  checking http   localhost 8080   If this returns with status code 500  the webserver will be restarted  The server will restart in under a minute  so there s no need to check for restarts already running   The server in question is a ubuntu 8 04 minimal installation with just enough packages installed to run what it currently needs  There is no hard requirement to do the task in bash  but I d like it to run in such a minimal environment without installing any more interpreters     I m sufficiently familiar with scripting that the command options to assign the http status code to an environment variable would be enough - this is what I ve looked for and could not find

User · Answer

To follow 3XX redirects and print response codes for all requests   HTTP STATUS    curl -IL --silent example com   grep HTTP         echo    HTTP STATUS

User · Answer

curl --write-out    http code  n  --silent --output  dev null   URL    works  If not  you have to hit return to view the code itself

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this can help to evaluate http status  var  curl -I http   www example org 2 gt  dev null   head -n 1   awk -F      print  2    echo http  var

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Here is my implementation  which is a bit more verbose than some of the previous answers  curl https   somewhere com somepath     --silent   --insecure   --request POST   --header  your-curl-may-want-a-header    --data  my input file   --output site output   --write-out   http code       gt  http response code 2 gt  error messages errorLevel    httpResponse   cat http response code    jq --raw-output  keys    csv  site output   sed  s    g   gt  return keys hasErrors  grep --quiet --invert errors return keys echo      if     errorLevel -gt 0           hasErrors -gt 0            httpResponse      200      then   echo -e  Error POSTing https   somewhere com somepath with input my input  errorLevel  errorLevel  http response code  httpResponse    gt  gt  error messages   send exit message   external function to send error messages to whoever  fi

User · Answer

To add to  DennisWilliamson comment above       VaibhavBajpai  Try this  response   curl --write-out  n  http code  --silent --output - servername  - the last line in the result will be the response code   You can then parse the response code from the response using something like the following  where X can signify a regex to mark the end of the response  using a json example here   X       code   echo   response   X     See Substring Removal  http   tldp org LDP abs html string-manipulation html

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I haven t tested this on a 500 code  but it works on others like 200  302 and 404  response   curl --write-out    http code   --silent --output  dev null servername   Note  format provided for --write-out should be quoted  As suggested by  ibai  add --head to make a HEAD only request  This will save time when the retrieval is successful since the page contents won t be transmitted

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Here comes the long-winded     yet easy to understand     script  inspired by the solution of nicerobot  that only requests the response headers and avoids using IFS as suggested here  It outputs a bounce message when it encounters a response    400  This echo can be replaced with a bounce-script     set the url to probe url  http   localhost 8080    use curl to request headers  return sensitive default on timeout   timeout 500    Parse the result into an array  avoid settings IFS  instead use read  read -ra result  lt  lt  lt    curl -Is --connect-timeout 5    url      echo  timeout 500     status code is second element of array  result  status   result 1     if status code is greater than or equal to 400  then output a bounce message  replace this with any bounce script you like     status -ge 400     amp  amp  echo  bounce at  url with status  status

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I needed to demo something quickly today and came up with this   Thought I would place it here if someone needed something similar to the OP s request      bin bash  status code   curl --write-out   http code  --silent --output  dev null www bbc co uk news   if      status code  -ne 200      then   echo  Site status changed to  status code    mail -s  SITE STATUS CHECKER   my email email com  -r  STATUS CHECKER  else   exit 0 fi   This will send an email alert on every state change from 200  so it s dumb and potentially greedy   To improve this  I would look at looping through several status codes and performing different actions dependant on the result

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Although the accepted response is a good answer  it overlooks failure scenarios  curl will return 000 if there is an error in the request or there is a connection failure   url  http   localhost 8080   status   curl --head --location --connect-timeout 5 --write-out   http code  --silent --output  dev null   url       status    500           status    000     amp  amp  echo restarting   url    do start restart logic   Note  this goes a little beyond the requested 500 status check to also confirm that curl can even connect to the server  i e  returns 000    Create a function from it   failureCode         local url   1 -http   localhost 8080      local code   2 -500      local status   curl --head --location --connect-timeout 5 --write-out   http code  --silent --output  dev null   url           status      code            status    000        Test getting a 500   failureCode http   httpbin org status 500  amp  amp  echo need to restart   Test getting error connection failure  i e  000    failureCode http   localhost 77777  amp  amp  echo need to start   Test not getting a 500   failureCode http   httpbin org status 400    echo not a failure

User · Answer

With netcat and awk you can handle the server response manually   if netcat 127 0 0 1 8080  lt  lt EOF   awk  NR  1 if   2     500   exit 0  exit 1     then GET   HTTP 1 1 Host  www example com  EOF      apache2ctl restart  fi

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i didn t like the answers here that mix the data with the status  found this  you add the -f flag to get curl to fail and pick up the error status code from the standard status var      https   unix stackexchange com questions 204762 return-code-for-curl-used-in-a-command-substitution  i don t know if it s perfect for every scenario here  but it seems to fit my needs and i think it s much easier to work with

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Another variation          status   curl -sS  -I https   www healthdata gov user login  2 gt   dev null   head -n 1   cut -d    -f2  status w desc   curl -sS  -I https   www healthdata gov user login  2 gt   dev null   head -n 1   cut -d    -f2-

[http] How to evaluate http response codes from bash/shell script?

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