022-timein.sh

#!/bin/sh

# timein - show the current time in the specified timezone or 
#   geographic zone. Without any argument, show UTC/GMT. Use
#   the word "list" to see a list of known geographic regions
#   Note that it's possible to match a zone directory (a region)
#   but that only timezone files are valid specifications.

#   Timezone database ref: http://www.twinsun.com/tz/tz-link.htm

zonedir="/usr/share/zoneinfo"

if [ ! -d $zonedir ] ; then
  echo "No timezone database at $zonedir." >&2 ; exit 1
fi

if [ -d "$zonedir/posix" ] ; then
  zonedir=$zonedir/posix        # modern Linux systems
fi

if [ $# -eq 0 ] ; then
  timezone="UTC"
  mixedzone="UTC"
elif [ "$1" = "list" ] ; then
  ( echo "All known timezones and regions defined on this system:"
    cd $zonedir
    find * -type f -print | xargs -n 2 | \
      awk '{ printf "  %-38s %-38s\n", $1, $2 }' 
  ) | more
  exit 0
else

  region="$(dirname $1)"
  zone="$(basename $1)"

  # Is it a direct match?  If so,  we're good to go. Otherwise we need 
  # to dig around a bit to find things. Start by just counting matches

  matchcnt="$(find $zonedir -name $zone -type f -print |
        wc -l | sed 's/[^[:digit:]]//g' )"

  if [ "$matchcnt" -gt 0 ] ; then       # at least one file matches
    if [ $matchcnt -gt 1 ] ; then       # more than one file match
      echo "\"$zone\" matches more than one possible time zone record." >&2
      echo "Please use 'list' to see all known regions and timezones" >&2
      exit 1
    fi
    match="$(find $zonedir -name $zone -type f -print)"
    mixedzone="$zone" 
  else
    # Normalize to first upper, rest of word lowercase for region + zone
    mixedregion="$(echo ${region%${region#?}} | tr '[[:lower:]]' '[[:upper:]]')\
$(echo ${region#?} | tr '[[:upper:]]' '[[:lower:]]')"
    mixedzone="$(echo ${zone%${zone#?}} | tr '[[:lower:]]' '[[:upper:]]')\
$(echo ${zone#?} | tr '[[:upper:]]' '[[:lower:]]')"
    
    if [ "$mixedregion" != "." ] ; then
      # only look for specified zone in specified region
      # to let users specify unique matches when there's more than one
      # possibility (e.g., "Atlantic")
      match="$(find $zonedir/$mixedregion -type f -name $mixedzone -print)"
    else
      match="$(find $zonedir -name $mixedzone -type f -print)"
    fi

    if [ -z "$match"  ] ; then  # no file matches specified pattern
      if [ ! -z $(find $zonedir -name $mixedzone -type d -print) ] ; then
        echo \
    "The region \"$1\" has more than one timezone. Please use 'list'" >&2
      else  #  just not a match at all
        echo "Can't find an exact match for \"$1\". Please use 'list'" >&2
      fi
      echo "to see all known regions and timezones." >&2
      exit 1
    fi
  fi
  timezone="$match"
fi

nicetz=$(echo $timezone | sed "s|$zonedir/||g")     # pretty up the output

echo It\'s $(TZ=$timezone date '+%A, %B %e, %Y, at %l:%M %p') in $nicetz

exit 0