Bash script to rename screen capture files on MacOSX to something cleaner. It's handy to attach this as a "folder action" so that files get renamed automagically. See http://apple.stackexchange.com/a/112747/27434

fixScreenCapFilenames.sh

#!/bin/bash
# -*- mode:shell-script; coding:utf-8; -*-
#
# Rename screenshot files to cleaner names, names for which a
# lexicographic sort is equivalent to a time-based sort.
#
# 
# Created: <Wed Dec  4 10:24:15 2013>
# Last Updated: <2013-December-04 13:57:46>
#

IFS=$'\n'
targdir=/Users/${USER}/Desktop
pattern=Screen\ Shot\ ????-??-??\ at\ *M.png 


cd $targdir
files="$(find . -iname "$pattern" -type f -print)"
if [ -n "$files" ]; then
  count=$(echo "$files" | wc -l)
else 
  count=0
fi


if [ $count -gt 0 ]; then
  ix=1
  for item in ${files} ; do
      printf "%d. %-18s\n" $ix "$item"
      # strip dot-slash
      fname=${item:2}  
      IFS=$' '
      parts=(${fname// / })
      # for part in ${parts} ; do
      #   echo $part
      # done
      #echo parts count: ${#parts}

      fdate=${parts[2]}
      ftime=${parts[4]}
      fdate=(${fdate//-/ })
      ftime=(${ftime//./ })
      suffix=${parts[5]}
      suffix=${suffix:0:2}
      #echo suffix: ${suffix}
      if [[ $suffix =~ ^PM ]] ; then 
          if ! [[ $ftime[0] =~ 12 ]]; then
            # echo adding 12
            let "ftime[0]+=12"
          fi
      else   
          # prepend with a zero as necessary
          if [[ $ftime[0] =~ 12 ]]; then
            ftime[0]="00"
          else 
            tvar="00${ftime[0]}"
            ftime[0]=${tvar:(-2)}
          fi
      fi
      newname="screenshot-${fdate[0]}${fdate[1]}${fdate[2]}-${ftime[0]}${ftime[1]}${ftime[2]}.png"
      
      if ! [ -f ${newname} ]; then
        echo new name: $newname
        mv "${fname}" "${newname}"
      fi 

      IFS=$'\n'
      let "ix+=1"
  done
fi