Question

In bash shell, how can be value checked if within range by most effective way?

Example:

     now=`date +%H%M`

     if [ $now -ge 2245 ] && [ $now -le 2345 ] ; then
     ...
     fi

…this one is working, but with using now variable.

Other option is:

     if [ $((`date +%H%M`)) -ge 2245 ] && [ $((`date +%H%M`)) -le 2345 ] ; then
     ...
     fi

…without variable, but with execution of date twice.

How to do it with one date execution and no variable at all?

Answer 1

First off, as a general rule, I’m pretty sure you need EITHER to use a variable OR run the command twice to do multiple comparisons on arbitrary numbers. There is no such notation as if [ 1000 -lt $(date '+%H%M') -lt 2000 ];.

Also, you don’t need to put your backquoted commands inside $((…)). The result of the backquoted command is a string which /bin/[ will be interpreted by -gt or -le as a number.

if [ `date '+%H%M'` -gt 2245 -a `date '+%H%M'` -lt 2345 ]; then

That said, as an option for the times in your example, you can try using a smarter date command line.

In FreeBSD:

if [ `date -v-45M '+%H'` -eq 22 ]; then

Or in Linux:

if [ `date -d '45 minutes ago' '+%H'` -eq 22 ]; then