I need to create a loop in bash to join images vertically and ouput multiple joined Pages for print

Question

I am running Ubuntu 18.04. I have a directory full of storyboard images in .jpg format as below.

image-0000.jpg
image-0001.jpg
image-0002.jpg
image-0003.jpg
image-0004.jpg
.
.
image-3898.jpg
image-3899.jpg

Merging 13 images vertically gives me a Single page. So I think I need to use below command, using a range of 13 numbers at a time in a loop and save to a directory "./Merged".

convert -append image-{range of 13}.jpg ./Merged/page_001.jpg

My experiment and thought process is as below.

I am trying to use a nested for loop and seq -w as below. But I am unable understand, how to loop the scrip in such a way that it takes first 13 files (from image-0000 to image-0012), merges them and saves in the ./Merged/ folder. Then come out of the loop and again take the next 13 files (from image-0013 to image-0025) and so on. Till all .jpg files in the current folder are finished or till 300 pages are generated.

My Script

#!/bin/bash
As 3899 image slices will be converted to 300 pages
I thought to run for loop 300 times
for ((page=1; page<=300; page++))
do
As images are slices of pages.
for slices in $(seq -w 0 3899)
   do
# We need to merge 13 times so...
# Should i use for loop with increment as below?
# for ((smerge=1; smerge&lt;=13; smerge++))
# do
#   convert &quot;SOME LOGIC&quot; ./Merged/page_001.jpg
# done

# **OR**
# somehow take 13 numbers from sequence

    convert image-$slices_{RANGE}.jpg -append ./Merged/page_$page.jpg 


done
done

Answer 1

So let's say you have these files in a continuous range from image-0000.jpg to image-2999.jpg. This should demonstrate the principle at work here:

#!/bin/bash
for page in {000..001}; do
  echo image-${page}{0..9}.jpg
done

So, do drop this into your use-case:

#!/bin/bash
for page in {000..001}; do
  convert image-${page}{0..9}.jpg --append ./Merged/page-${page}.jpg
done

_{Note that {01..02} expanding to 01 02 rather than 1 2 requires bash 4.}

Answer 2

With zsh:

#! /bin/zsh -

typeset -Z3 page
files=(image-<0-3900>.jpg)
for ((page = 1; $#files; page++)) {
  convert $files[1,13] -append ./Merged/page_$page.jpg
  files[1,13]=()
}

Note that since there are 3901 images (13 × 300 + 1), the last page will have only one image.

You can do something similar with bash like:

#! /bin/bash -
shopt -s extglob
shopt -s failglob
set -- image-+([[:digit:]]).jpg
for ((page = 1; $#; page++)) {
  printf -v padded_page %03d "$page"
  convert "${@:1:13}" -append "./Merged/page_$padded_page.jpg"
  (($# > 13)) || break
  shift 13
}

POSIXly, assuming there are matching files and doing a yet less close check on file names:

#! /bin/sh -
set -- image-*.jpg

# disable split+glob, only retain empty removal on unquoted expansions:
set -o noglob; IFS=

page=1; while [ "$#" -gt 0 ]; do
  padded_page=000$page
  padded_page=${padded_page#"${padded_page%???}"}
  convert $1 $2 $3 $4 $5 $6 $7 $8 $9 ${10} ${11} ${12} ${13} \
    -append "./Merged/page_$padded_page.jpg"
  [ "$#" -gt 13 ] || break
  shift 13
  page=$((page + 1))
done

Note that while here the file names are very tamed (no blanks, special characters...), special care has been taken in those codes to handle arbitrary characters. However note that convert and other imagemagick utilities could have problems with file names starting with - (even when using --) or containing :, so best is to prefix file paths with ./ to avoid those problems (for instance, use ./*.jpg instead of *.jpg).

Answer 3

You can do this using xargs -n argument and push the result to a while read loop.

page=1
while IFS= read -r row; do
    convert $row -append ./Merged/page_$page.jpg
    page=$((page + 1))
done < <(echo image-{0000..3900}.jpg | xargs -n13)

Answer 4

Hello everyone. Thank you very much for your time and replies.

DopeGhoti, Philip Kendall, Stéphane Chazelas, RoVo

This is What I was able to create, and it worked. Still I would like to check others Solution too. Maybe your solution is faster than my basic Script.

NOTE: This Script will/might fail if there are spaces in file names!

only script

#!/bin/bash
NOTE: This Script will/might fail if there are spaces in file names!
mkdir -p Finished;
mkdir -p Merged;
for paGe in $(seq -w 1 300)
do
   ls *.jpg | head -n 13 > filesData.txt;
   paGeData=$(sed ':a;N;$!ba;s/\n/ /g' filesData.txt);
   convert $paGeData -append ./Merged/Page_$paGe.jpg;
while read -r line
   do
      mv $line ./Finished/
   done < filesData.txt
done

Script with comments

#!/bin/bash
NOTE: This Script will/might fail if there are spaces in file names!
I random capitalize letters in a variable to make them unique,
As i can't be sure.
mkdir -p Finished;
mkdir -p Merged;
for paGe in $(seq -w 1 300)
do
Selecting only 13 files from the current directory
ls *.jpg | head -n 13 > filesData.txt;
Replace newline (\n) with space and place "file names"
in one line and storing "sed" output to a variable.
So that we use it with "convert" command.
paGeData=$(sed ':a;N;$!ba;s/\n/ /g' filesData.txt);
Merge different images to one long image
convert $paGeData -append ./Merged/Page_$paGe.jpg;
Move files to different directory,
So that we can work with next range/batch of files.
while read -r line
   do
      mv $line ./Finished/
   done < filesData.txt
done

A long thought process. If someone might be interested in how I tried to improvise the code. This might have some mistakes.

#!/bin/bash
mkdir -p Finished;
mkdir -p Merged;
for paGe in $(seq -w 1 300)
do
Selecting only 13 files from the current directory
ls *.jpg | head -n 13 > filesData.txt;
Replace newline (\n) with space and
place file names in one line for the convert command in while loop
sed ':a;N;$!ba;s/\n/ /g' filesData.txt > paGeData.txt;
We can remove below loop by storing sed (above) output to a variable
and substituting it later in the command.
paGeData=$(sed ':a;N;$!ba;s/\n/ /g' filesData.txt);
Merge different images to one long image
"line" is a system variable
while read -r line
do
convert $line -append ./Merged/Page_$paGe.jpg
done < paGeData.txt
convert $paGeData -append ./Merged/Page_$paGe.jpg;
Move files to different directory,
So that we can work with next range/batch of files.
while read -r line
   do
      mv $line ./Finished/
   done < filesData.txt
done