Bourne shell functions to show informal English time spans

duration.sh

# Some handy informal duration functions in Bourne shell (bash is fine, too).

# duration(): 	given seconds, returns commonsense equivalent duration.

# ago(): 	given seconds from epoch, compares to current time.

# howlongago(): show how long ago a file or subdir was last modified.
#		given a file, shows how long ago that file was updated.
#		given a directory, recursively searches for most
#				   recently changed FILE (not directory)
#		given no argument, searches the current working directory.


# Examples:
#
#  $ howlongago /etc/passwd
#  Last updated 3 months, 15 weeks ago
#
#  $ howlongago /var/www	# searches recursively for most recent file
#  Last updated 1 day, 0 hours ago
#
#  $ howlongago			# no argument checks current working directory
#  Last updated 5 minutes, 57 seconds ago
#
#  $ duration $((10**9))  	# how long is a billion seconds?
#  31 years
#
#  $ ago 0			# How long ago was the Unix Epoch?
#  60 years ago
# 
#  $ date +%s
#  1912817946		        # Current number of seconds since the Epoch
#
#  $ ago $(date +%s)		# Of course, now is always now.
#  just now
#
#    				# "ago" isn't just for the past
#  $ ago $(date --date='next tuesday' +%s)
#  2 days, 20 hours from now
#
#				# how long until R's birthday?
#  $ ago $(date -d 'feb 11 next year' +%s)
#  2 months, 9 weeks from now


duration() {
    # Input number of seconds, print informal duration in English.
    # Shows two units of precision. (E.g., hours and minutes).

    # Inaccuracies that probably don't matter:
    # 1. Always rounds *down*.
    #    E.g. 1 hour, 59 minutes, 59 seconds => 1 hour, 59 minutes
    # 2. A month is precisely 30 days. This is, of course, not quite true.
    # 3. Similarly, a year is exactly 364 days.

    local s=$1; local m=$((s / 60));  local h=$((m / 60))
    local d=$((h / 24)); local w=$((d / 7)); local M=$((d / 30))
    local y=$((d / 364))
    if [ $s -lt 60 ]; then
        span="$s second`s $s`"
    elif [ $s -lt $((60*60)) ]; then
        s=$((s%60))
    	span="$m minute`s $m`, $s second`s $s`"
    elif [ $s -lt $((60*60*24)) ]; then
        m=$((m%60))
    	span="$h hour`s $h`, $m minute`s $m`"
    elif [ $s -lt $((60*60*24*7)) ]; then
        h=$((h%24))
    	span="$d day`s $d`, $h hour`s $h`"
    elif [ $s -lt $((60*60*24*30)) ]; then
        d=$((d%7))
    	span="$w week`s $w`, $d day`s $d`"
    elif [ $s -lt $((60*60*24*364)) ]; then
        w=$((w%30))
    	span="$M month`s $M`, $w week`s $w`"
    elif [ $s -lt $((60*60*24*364*10)) ]; then
        M=$((M%12))
    	span="$y year`s $y`, $M month`s $M`"
    else
    	span="$y year`s $y`"    # Stopping counting months after a decade
    fi
    echo "$span"
}

ago() {
    # Given a date (in seconds since The Epoch), print how long ago
    # that was from now, in informal English.
    local now=$(date +%s)
    local s=$((now - $1))
    if [ $s -eq 0 ]; then
        echo "just now"
    elif [ $s -gt 0 ]; then
        echo "$(duration $s) ago"
    else
        s=$((-s))
        echo "$(duration $s) from now"
    fi
}

howlongago() {
    # Given a directory or filename (or nothing for cwd), print how
    # recently it was last modified in informal English.

    # Note: Recursively searches directories for all files and reports
    # on the one most recently updated. Directories themselves are
    # *not* considered for comparison since they get modified by simple
    # things like renaming or copying a file.

    if [ -z "$1" ]; then
	dir="."
    else
	dir="$1"
    fi
    local mostrecent=$(find "$dir" -type f -printf '%T@\n' | cut -d. -f1 | sort -n | tail -n1)
    if [ -z "$mostrecent" ]; then
       echo "No files found" 
       return
    fi

    echo "Last updated $(ago $mostrecent)"
}

s() {
    if [ $1 -ne 1 ]; then echo -n "s"; fi
}


# TODO
    # Maybe consider adding support for something larger than "years".
    # 
    # Decades don't  work since nobody talks about "4 decades and 7 years".
    # We could use "score", for twenty years, but that's just weird.

    # In English, what happens is people start rounding to the nearest
    # decade at some point, as in: "over 130 years ago". Perhaps, I
    # should start after a century?