Manual Pages  — SLEEP

The sleep command allows and honors a non-integer number of seconds to sleep in any form acceptable by strtod(3). This is a non-portable extension, and its use will nearly guarantee that a shell script will not execute properly on another system.

    (sleep 1800; sh command_file >& errors)&

This incantation would wait a half hour before running the script command_file. (See the at(1) utility.)

To reiteratively run a command (with the csh(1)):

while (1)
        if (! -r zzz.rawdata) then
                sleep 300
        else
                foreach i (`ls *.rawdata`)
                        sleep 70
                        awk -f collapse_data $i >> results
                end
                break
        endif
end

The scenario for a script such as this might be: a program currently running is taking longer than expected to process a series of files, and it would be nice to have another program start processing the files created by the first program as soon as it is finished (when zzz.rawdata is created). The script checks every five minutes for the file zzz.rawdata, when the file is found, then another portion processing is done courteously by sleeping for 70 seconds in between each awk job.