Check if the current time falls within defined time range on UNIX

Question

Consider the below PSUEDO-CODE:

#!/bin/ksh

rangeStartTime_hr=13
rangeStartTime_min=56
rangeEndTime_hr=15
rangeEndTime_min=05


getCurrentMinute() {
    return `date +%M  | sed -e 's/0*//'`; 
    # Used sed to remove the padded 0 on the left. On successfully find&replacing 
    # the first match it returns the resultant string.
    # date command does not provide minutes in long integer format, on Solaris.
}

getCurrentHour() {
    return `date +%l`; # %l hour ( 1..12)
}

checkIfWithinRange() {
    if [[ getCurrentHour -ge $rangeStartTime_hr &&  
          getCurrentMinute -ge $rangeStartTime_min ]]; then
    # Ahead of start time.
        if [[  getCurrentHour -le $rangeEndTime_hr && 
                   getCurrentMinute -le $rangeEndTime_min]]; then
            # Within the time range.
            return 0;
        else
            return 1;
        fi
    else 
        return 1;   
    fi
}

Is there a better way of implementing checkIfWithinRange()? Are there any inbuilt functions in UNIX that make it easier to do the above? I am new to korn scripting and would appreciate your inputs.

What language or environment is this? The tags say `ksh` but that doesn't look like [Korn Shell](http://www.kornshell.com/) code. — Brian Campbell, Dec 05 '12 at 07:37
To expand on my question a bit, Unix is an operating system (a family of operating systems), not a programming language. How you interact with dates will depend more on your programming language than your operating system. The two standard programming environments on Unix are the shell and C, but your example code is neither. Yes, you are going to have to store a start time and end time, and compare them against your current time. How you do that depends on the language and environment you're using; a struct in C, variables or a file in the shell, an object in Java, columns in a database. — Brian Campbell, Dec 05 '12 at 07:48
@BrianCampbell Thanks! I am new to UNIX korn shell and wrote the sample pseudo-code that I want to implement in korn shell. Will update the question in a few minutes after I try it out myself. — Kent Pawar, Dec 05 '12 at 09:29

score 2 · Accepted Answer · edited Dec 08 '12 at 14:12

The return command is used to return an exit status, not an arbitrary string. This is unlike many other languages. You use stdout to pass data:

getCurrentMinute() {
    date +%M  | sed -e 's/^0//' 
    # make sure sed only removes zero from the beginning of the line
    # in the case of "00" don't be too greedy so only remove one 0
}

Also, you need more syntax to invoke the function. Currently you are comparing the literal string "getCurrentMinute" in the if condition

if [[ $(getCurrentMinute) -ge $rangeStartTime_min && ...

I would do if a bit differently

start=13:56
end=15:05

checkIfWithinRange() {
    current=$(date +%H:%M) # Get's the current time in the format 05:18
    [[ ($start = $current || $start < $current) && ($current = $end || $current < $end) ]] 
}

if checkIfWithinRange; then
    do something
fi

Thank you @glenn for the detailed explanation. Will confirm the code from my end and get back.. — Kent Pawar, Dec 07 '12 at 15:23

Check if the current time falls within defined time range on UNIX

1 Answers1