Pass .txt list of .jpgs to convert (bash) - bash

Question

I'm currently working on an exercise that requires me to write a shell script whose function is to take a single command-line argument that is a directory. The script takes the given directory, and finds all the .jpgs in that directory and its sub-directories, and creates an image-strip of all the .jpgs in order of modification time (newest on bottom).
So far, I've written:
#!bin/bash/
dir=$1 #the first argument given will be saved as the dir variable
#find all .jpgs in the given directory
#then ls is run for the .jpgs, with the date format %s (in seconds)
#sed lets the 'cut' process ignore the spaces in the columns
#fields 6 and 7 (the name and the time stamp) are then cut and sorted by modification date
#then, field 2 (the file name) is selected from that input
#Finally, the entire sorted output is saved in a .txt file
find "$dir" -name "*.jpg" -exec ls -l --time-style=+%s {} + | sed 's/ */ /g' | cut -d' ' -f6,7 | sort -n | cut -d' ' -f2 > jgps.txt
The script correctly outputs the directory's .jpgs in order of time modification. The part that I am currently struggling on is how to give the list in the .txt file to the convert -append command that will create an image-strip for me (For those who aren't aware of that command, what would be inputted is: convert -append image1.jpg image2.jpg image3.jpg IMAGESTRIP.jpgwith IMAGESTRIP.jpg being the name of the completed image strip file made up of the previous 3 images).
I can't quite figure out how to pass the .txt list of files and their paths to this command. I've been scouring the man pages to find a possible solution but no viable ones have arisen.

Answer 1

xargs is your friend:
find "$dir" -name "*.jpg" -exec ls -l --time-style=+%s {} + | sed 's/ */ /g' | cut -d' ' -f6,7 | sort -n | cut -d' ' -f2 | xargs -I files convert -append files IMAGESTRIP.jpg
Explanation
The basic use of xargs is:
find . -type f | xargs rm
That is, you specify a command to xargs, it appends the arguments it receives from standard input and then executes it. The avobe line would execute:
rm file1 file2 ...
But you also need to specify a final argument to the command, so you need to use the xarg -I parameter, which tells xargs the string you will use after to indicate where the arguments read from standard input will be put.
So, we use the string files to indicate it. Then we write the command, putting the string files where the variable arguments will be, resulting in:
xargs -I files convert -append files IMAGESTRIP.jpg

Answer 2

Put the list of filenames in a file called filelist.txt and call convert with the filename prepended by an ampersand:
convert #filelist.txt -append result.jpg
Here's a little example:
# Create three blocks of colour
convert xc:red[200x100] red.png
convert xc:lime[200x100] green.png
convert xc:blue[200x100] blue.png
# Put their names in a file called "filelist.txt"
echo "red.png green.png blue.png" > filelist.txt
# Tell ImageMagick to make a strip
convert #filelist.txt +append strip.png
As there's always some image with a pesky space in its name...
# Make the pesky one
convert -background black -pointsize 128 -fill white label:"Pesky" -resize x100 "image with pesky space.png"
# Whack it in the list for IM
echo "red.png green.png blue.png 'image with pesky space.png'" > filelist.txt
# IM do your stuff
convert #filelist.txt +append strip.png
By the way, it is generally poor practice to parse the output of ls in case there are spaces in your filenames. If you want to find a list of images, across directories and sort them by time, look at something like this:
# Find image files only - ignoring case, so "JPG", "jpg" both work
find . -type f -iname \*.jpg
# Now exec `stat` to get the file ages and quoted names
... -exec stat --format "%Y:%N {} \;
# Now sort that, and strip the times and colon at the start
... | sort -n | sed 's/^.*://'
# Put it all together
find . -type f -iname \*.jpg -exec stat --format "%Y:%N {} \; | sort -n | sed 's/^.*://'
Now you can either redirect all that to filelist.txt and call convert like this:
find ...as above... > file list.txt
convert #filelist +append strip.jpg
Or, if you want to avoid intermediate files and do it all in one go, you can make this monster where convert reads the filelist from its standard input stream:
find ...as above... | sed 's/^.*://' | convert #- +append strip.jpg