How to use two FOR Loop in bash

Question

Can someone help me look into this? I'm trying to use Imagemagick to merge two images. One is a plain text, while the other one has a nice background. I have more than 12,000 plain text and 82 background images, so I have to construct two FOR loop to be able to pick both images randomly. But unfortunately, the second loop is not working for the background images. It only picks one and merge it with all plain text instead of random. The following is how I am implementing it.

for i in $(find /home/user/png -name "*.png"); do 
    for o in $(find /home/user/jpg -name "*.jpg"); do 
       composite -gravity Center $i $o "${i%.*}.jpg"; 
    done
done

You shouldn't be using any for loops here. See mywiki.wooledge.org/DontReadLinesWithFor. — chepner
– chepner, Commented Jul 2, 2017 at 21:17

janos · Accepted Answer · 2017-07-03 06:31:59Z

1

For the fact that i have more than 12,000 plain text an 82 Background so i have to construct two FOR loop for to be able to pick both image randomly.

If the background and image file paths don't contain whitespace characters, then the following technique should work. Replace all the find ... appropriately.

You could put the 82 background files into an array:

backgrounds=($(find ...))

Define a function to pick a random background:

randombg() {
    local index
    ((index = RANDOM % ${#backgrounds[@]}))
    echo ${backgrounds[index]}
}

And then loop over the image files, and for each file, pick a random background:

find ... | while read image; do
   bg=$(randombg)
   composite -gravity Center $image $bg "${image%.*}.jpg"
done

edited Jul 3, 2017 at 6:31

answered Jul 2, 2017 at 18:54

janos

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1 Comment

Yusuf Adeyemo Over a year ago

I can't thank you enough for helping me. This works like charm.

agc · Accepted Answer · 2017-07-03 13:25:50Z

1

Using the shuf command to create an endless stream of shuffled *.jpg files, which within the for loop are input with read o:

shuf -r -e $(find /home/user/jpg -name "*.jpg") | 
for i in   $(find /home/user/png -name "*.png") ; do 
    read o
    composite -gravity Center "$i" "$o" "${i%.*}.jpg"
done

Since there are no bash arrays, the above code is POSIX by default.

edited Jul 3, 2017 at 13:25

answered Jul 3, 2017 at 13:20

agc

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