How to deal with NFS latency in shell scripts

Question

I'm writing shell scripts where quite regularly some stuff is written to a file, after which an application is executed that reads that file. I find that through our company the network latency differs vastly, so a simple sleep 2 for example will not be robust enough.

I tried to write a (configurable) timeout loop like this:

waitLoop()
{
   local timeout=$1
   local test="$2"

   if ! $test
   then
      local counter=0
      while ! $test && [ $counter -lt $timeout ]
      do
         sleep 1
         ((counter++))
      done

      if ! $test
      then
         exit 1
      fi
   fi
}

This works for test="[ -e $somefilename ]". However, testing existence is not enough, I sometimes need to test whether a certain string was written to the file. I tried test="grep -sq \"^sometext$\" $somefilename", but this did not work. Can someone tell me why?

Are there other, less verbose options to perform such a test?

Answer 1

You can set your test variable this way:

test=$(grep -sq "^sometext$" $somefilename)

The reason your grep isn't working is that quotes are really hard to pass in arguments. You'll need to use eval:

if ! eval $test