how to store result of tail command in variable?

Question

I am developing application in MEAN stack. I want to create a script of image resizing & cropping as a background process when new image uploads to server.

Script watches new image uploads in folder and crop it.

I preferred way of Linux shell scripting as daemon.

I have used following idea to accomplished tasks. - New image uploads on server it writes in photolog.txt file, where I can grab images line by line. - I read photolog.txt in watch.sh shell scripting file. - It Iterates through line by line, until it reaches to the EOL. - Again new file arrives it will append at EOL. - I manage to get updated file by tail command, and get the latest add file display in command-line. Upto this code it works charm.

Now I am successfully grab the image list of newly added file on server. but main issue is that I fails to store output of tail command in variable, and it must to me because whatever output I get it is full path of filename and it will use in imagemagick crop command.

Imagemagick center crop with scale an image.

convert -define file-type:size=widthxheight original_filename -thumbnail 120x120^ -gravity center -extent 100x100 resize_filename

watch.sh

#!/bin/bash
path="/var/www/html/AppBite/trunk/photolog.txt"
cat $path | \

until false
do
    # If file exists 
    if [[ -f "$path" ]]
    then    
        while IFS= read -r photo
        do
            imageFormat=`identify $photo | awk '{print $2}'`
            imageScale=`identify $photo | awk '{print $3}'`
            echo "$photo $imageFormat $imageScale"
        done
    fi
    # Continous monitor file changes via commandline
    tail -f $path
done

I am successfully grab command-line output but I am not able to store value in variable, for next use imagemagick image processing command.

or suggest me other way to continuous monitoring folder to get newly added file list.

Answer 1

Since tail -f doesn't terminate, you don't want to capture its output in a variable. But since you call it in a loop anyway, call it over and over like this:

OUT=`tail "$path"`

Or using the modern syntax:

OUT=$(tail "$path")