Error with find when using -newerct values stored in variables

Question

I'm trying to create a bash function that will use a simple file such as

sample.txt

start=22 Mar 2016 10:00
end=22 Mar 2016 12:09

...and find files that I have installed to /usr/local within the time range as specifed by start and end.

The function I created originally is:

function findInstalled () {
  if [[ $# -ne 1 ]]; then
    echo "[ERROR] Usage: findInstalled /path/to/file" ;
    return 1;
  fi

  start=$( grep start $1 | cut -d'=' -f2 ) ;
  end=$( grep end $1 | cut -d'=' -f2 ) ;

  if [[ ! -z $start ]]; then
    start="-newerct \"${start}\"" ;
  fi

  if [[ ! -z $end ]]; then 
    end="! -newerct \"${end}\"" ;
  fi
  echo find /usr/local $start $end -type f ;
  find /usr/local $start $end -type f ;
}

..and executing the function gives the following output:

$ findInstalled /path/to/sample.txt
find /usr/local -newerct "22 Mar 2016 10:00" ! -newerct "22 Mar 2016 12:09" -type f
find: I cannot figure out how to interpret `"22' as a date or time

The actual execution of the command gives the error ...cannot figure out how to interpret.... However, if I copy and paste the echo'ed version of the command it executes successfully. Any idea what the problem is? Note, I've tried with--and without--all kinds of different combinations of double qoutes and single qoutes and none of them have worked.

I have gotten the function to work, although not quite in the way that I wanted, by doing the following instead:

function findInstalled () {
  if [[ $# -ne 1 ]]; then
    echo "[ERROR] Usage: findInstalled /path/to/file"
    return 1;
  fi

  start=$( grep start $1 | cut -d'=' -f2 ) ;
  end=$( grep end $1 | cut -d'=' -f2 ) ;

  find /usr/local -newerct "$start" ! -newerct "$end" -type f ;
}

So, using this, I have managed to achieve my original goal, but I'm dying to find out why my original function does not work, or if it is even possible.

Answer 1

The problem is how the shell breaks the line into tokens. It expands $start into -newerct "22 Mar 2016 10:00", then splits words on spaces. Thus find is passed the following arguments: -newerct, "22, Mar, etc. hence the error message. man bash states:

The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion.

I'm not sure it can be done in the way you wanted. Your second script is more readable, but you have to make sure the variables are not null. Maybe you could do it like this:

find /usr/local ${start:+-newerct} "$start" ${end:+! -newerct} "$end" -type f ;