Unix script to compare a timestamp with current time

Question

This is my first journey into the realm of Unix scripting and I'm not sure how to go about this. Ill be querying a DB and pulling out a timestamp. What I need to do is take that timestamp (in the awesome format of YYYYMMDDHHMMSS) and if its more than 10 minutes old, return a 1 else return 0.

Again, I have essentially 0 experience with this type of scripting (background is in C++ and C#) so if you guys don't mind a little more explanation I'd be grateful - I want to learn how it works too.

Thanks!

Answer 1

The way your tools work depends on the flavour of Unix you use. The following should work in Linux, FreeBSD, NetBSD, OSX, etc.

#!/bin/sh

sample="${1:-20120306131701}"

if ! expr "$sample" : '[0-9]\{14\}$' >/dev/null; then
  echo "ERROR: unknown date format" >&2
  exit 65
fi

case $(uname -s) in
  *BSD|Darwin)
    # The BSD date command allows you to specify an input format.
    epoch=$(date -jf '%Y%m%d%H%M%S' "$sample" '+%s')
    ;;
  Linux)
    # No input format in Linux, so rewrite date to something '-d' will parse
    tmpdate="$(echo "$sample" | sed -r 's/(.{8})(..)(..)(..)/\1 \2:\3:\4/')"
    epoch=$(date -d "$tmpdate" '+%s')
    ;;
  *)
    echo "ERROR: I don't know how to do this in $(uname -s)." >&2
    exit 69
    ;;
esac

now=$(date '+%s')

# And with the provided datetime and current time as integers, it's MATH time.
if [ $((now - epoch)) -gt 600 ]; then
  exit 1
fi

exit 0

Note that this is a /bin/sh script, for the sake of portability, so it doesn't take advantage of bash-isms you may be used to in Linux, in particular [[ ... ]] and heretext to read variables.

Oh, and I'm assuming that you meant "exit value" when you said "return value". A return value would be the result of a function, but what I've written above is a stand-alone script.

Note that this may not understand timestamps in the future, nor does it take timezone into consideration. If that's important to you, you should, er, consider it. :-) And test in your environment.