order for listing files

Question

If I have a list of files under a directory

ullman-000.pbm
ullman-001.pbm
...
ullman-098.pbm
ullman-099.pbm
ullman-1000.pbm
ullman-1001.pbm
ullman-1002.pbm
ullman-1003.pbm
ullman-1004.pbm
ullman-1005.pbm
ullman-1006.pbm
ullman-1007.pbm
ullman-1008.pbm
ullman-1009.pbm
ullman-100.pbm
ullman-1010.pbm
ullman-1011.pbm
ullman-1012.pbm
ullman-1013.pbm
ullman-1014.pbm
ullman-1015.pbm
ullman-1016.pbm
...

When using ullman*.pbm to refer to them and pass it to command convert ullman*.pbm ullman.pdf as input files, how can I make them in the order of

ullman-000.pbm
ullman-001.pbm
...
ullman-098.pbm
ullman-099.pbm
ullman-100.pbm
...
ullman-999.pbm
ullman-1000.pbm
ullman-1001.pbm
ullman-1002.pbm
ullman-1003.pbm
ullman-1004.pbm
ullman-1005.pbm
ullman-1006.pbm
ullman-1007.pbm
ullman-1008.pbm
ullman-1009.pbm
ullman-1010.pbm
ullman-1011.pbm
ullman-1012.pbm
ullman-1013.pbm
ullman-1014.pbm
ullman-1015.pbm
ullman-1016.pbm
...

Thanks?

Answer 1

GNU sort and xargs might do the trick

printf '%s\0' ullman*.pbm | sort -z -k2,2n -t'-' | xargs -0 convert 

First check this works by listing files without calling convert

printf '%s\0' ullman*.pbm | sort -z -k2,2n -t'-' | xargs -0 printf '%s\n'
ullman-000.pbm
ullman-001.pbm
ullman-098.pbm
ullman-099.pbm
ullman-100.pbm
ullman-1000.pbm
...

Whereas

printf '%s\0' ullman*.pbm  | xargs -0 printf '%s\n'                                                              
ullman-000.pbm
ullman-001.pbm
ullman-098.pbm
ullman-099.pbm
ullman-1000.pbm
..
..

Answer 2

One way would be to rename the files that have three digit numbers to four digit ones, padded with a zero. If you have perl-rename (installed by default on Ubuntu) you can try:

rename -n 's/-(\d{3}\.)/-0$1/' *.pbm

Once you're satisfied with the result, run again without the -n.

Or see other options in Padding a number in a filename to a fixed length.