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I have the following script:

#!/bin/bash
y=$(ls -t ./pics/0/*.png | head -n 2 | tail -n 1)
new=$(ls -t ./pics/0/*.png | head -n 1)
while true
do
 if cmp --silent "$y" "$new" ; then
y=$(ls -t ./pics/0/*.png | head -n 1)
    base64 $y | tr -d '\n' | sed '$ a \'
new=$(ls -t ./pics/0/*.png | head -n 1)
 fi
done

What am I doing wrong? To be clear my goal is to compare whether the newest file is different from the previous newest file and only if it is generate a unique BASE64 to STDOUT (meaning it should be printed only ONCE).

Sir Muffington
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  • You are missing spaces in your if. It is if [ cmp --silent $y $new != null ]. – schrodingerscatcuriosity Aug 19 '19 at 19:21
  • @guillermochamorro Now it says that I've got too many arguments.. – Sir Muffington Aug 19 '19 at 19:24
  • @steeldriver this code works, but the script prints out multiple duplicate base64 strings, I probably made a logical error in doing the script then? any clue how to fix it so that prints unique base64 every time a file is changed? – Sir Muffington Aug 19 '19 at 19:32
  • Removing the --silent flag seems to reduce the number of occurrences of base64 strings to only 3-4 per second, when a new file is added every second. Is this a bug??? – Sir Muffington Aug 19 '19 at 20:03
  • It also spams my STDERR with argument list too long on my cmp line... So I guess the errors are making it slow down.. – Sir Muffington Aug 19 '19 at 20:11
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    Please take a look: http://www.shellcheck.net/ – Cyrus Aug 19 '19 at 21:06
  • The code has now an extra then. – schrodingerscatcuriosity Aug 19 '19 at 21:35
  • $x -le 5 You don't have in your code an update of the x value. The expression is always true, which makes it an infinite loop. – schrodingerscatcuriosity Aug 19 '19 at 21:44
  • to start with, you are comparing the value 0 (y=0) with a list of files ($new). this won't work. cmp takes exactly two filename arguments. 0 is probably not a filename, and $new can contain 0, 1, or any number of filenames. – cas Aug 20 '19 at 01:01
  • try y="$(ls -t ./pics/0/*.png | head -n 2 | tail -n 1)" and new="$(ls -t ./pics/0/*.png | head -n 1)". i have no idea what the rest of your script is meant to do because it makes little or no sense. – cas Aug 20 '19 at 01:03
  • it's supposed to be an infinite loop. @cas I edited the code accordingly now it doesn't print anything.. – Sir Muffington Aug 20 '19 at 10:12
  • why [ -z "$(cmp ...)" ]? You want to test the exit code from cmp, not its output (which is typically empty). Use if cmp "$y" "$new" ; then instead. – cas Aug 20 '19 at 10:15
  • and if you want an endless loop, use while true; do ........ ; done. Testing for [ $x -le 5 ] just makes it look like you forgot to increment $x. – cas Aug 20 '19 at 10:17
  • @cas now it just spams me with standard output ./pics/0/out12:17:02.747683.png ./pics/0/out12:17:03.765651.png differ: char 36, line 3. If I add the --silent flag back it doesn't do anything at all.. – Sir Muffington Aug 20 '19 at 10:18
  • For people wondering what | tr -d '\n' | sed '$ a \' does: it's for formatting the message, it first removes all newlines if there are any and puts one at the end. – Sir Muffington Aug 20 '19 at 12:07

1 Answers1

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Please note that the following snippet will NOT work with filenames containing spaces, tabs or newlines.

To find out more about the find-command used here, please reference https://unix.stackexchange.com/a/240424/364705 

#!/bin/bash
lastrun=''
while true; do
  read -r newer older <<< \
    $(find . -type f -exec stat -c '%Y %n' {} \; \
    | sort -nr \
    | awk 'NR==1,NR==2 {print $2}'\
    | xargs )

  if [ "$newer" == "$lastrun" ]; then
    :
  else
    if ! cmp "$newer" "$older" > /dev/null ; then
      base64 "$newer"| tr -d '\n' | sed '$ a \'
      lastrun="$newer"
    fi
  fi
done

And a solution using inotify-wait:

#!/bin/bash
lastfile=''
inotifywait -m /path/to/somewhere -e close -e moved_to |
while read path action file; do
  if [ "$lastfile" != '' ];then
    if ! cmp "${path}$file" "${path}${lastfile}" > /dev/null  ; then
    base64 "${path}${file}"
    fi
  fi
    lastfile="$file"
done
markgraf
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