Execute command on a pair of files

Question

Context :I've scanned a lot of old pictures, that have writing on the back.

Using imagemagick, I can append the front and back of the picture like this :

montage out20.jpg out21.jpg -gravity center -geometry +1+1 -tile 1x2 out2021.jpg; rm out20.jpg out21.jpg;
#(vertical append)

My problem is that I have a lot of pictures to apply the command on.

Is there a way to ask bash to apply "montage" to each odd file, adding automaticly the filename that comes after it ? The output filename is also a problem.

Answer 1

Quick and dirty:

#!/bin/bash
ls *.jpg | while read file
do
  number=`echo $file | tr -dc 0-9`;
  if [ $((number % 2)) -eq 0 ]; then
    nextnumber=`echo $number + 1 | bc`;
    nextfile=`echo $file | sed s/$number/$nextnumber/`;
    outfile=`echo $file | sed s/$number/$number$nextnumber/`;
    montage $file $nextfile -gravity center -geometry +1+1 -tile 1x2 $outfile
  fi
done

You said to apply the montage to the odd files but provided even in your example. The code above will work for even. If you need the odd files to be first just change this line:

if [ $((number % 2)) -eq 0 ]; then

to be this:

if [ $((number % 2)) -eq 1 ]; then