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Lcross Portugal
Asked: 2015-05-06 11:33:17 +0800 CST

Script to generate thumbs only if thumb doesn't exist

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I have a working script to generate thumbs to all pdf files in a folder( using Image Magic):

for f in *.pdf; do convert -thumbnail 250x200 "$f"[0]"_thumb_wd_${f%.pdf}.jpg"; done

How can i adjust this to check if the "_thumb_wd_+"f"+.jpg exists? So i can generate the thumbs only if it does not exists!

bash

1 Answers

  1. You can use if conditional construct to perform an action depending on some condition e.g. if something exists or not. In your case you need to put the action segment inside the if-then condition:

      if ! [[ -f "_thumb_wd_${f%.pdf}.jpg" ]]; then
    convert -thumbnail 250x200 "$f"[0]"_thumb_wd_${f%.pdf}.jpg"
  fi

    [[ is a bash keyword, we are using it to check (-f) if the file _thumb_wd_${f%.pdf}.jpg exists and is a regular file. The ! negates the operation, as a result convert will only run if the file does not exist.

    So, your final script:

    #!/bin/bash
for f in *.pdf; do
  if ! [[ -f "_thumb_wd_${f%.pdf}.jpg" ]]; then
    convert -thumbnail 250x200 "$f"[0]"_thumb_wd_${f%.pdf}.jpg"
  fi
done
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