If I have these files in a directory
cwcch10.pdf cwcch11.pdf cwcch12.pdf cwcch13.pdf cwcch14.pdf cwcch15.pdf cwcch16.pdf cwcch17.pdf cwcch18.pdf cwcch1.pdf cwcch2.pdf cwcch3.pdf cwcch4.pdf cwcch5.pdf cwcch6.pdf cwcch7.pdf cwcch8.pdf cwcch9.pdf
how can I list them in Bash so that they are in ascending numeric order based on the number part of the string. So the resulting order is
cwcch1.pdf, cwcch2.pdf, ..., cwcch9.pdf, cwcch10.pdf, etc.
What I'm ultimately trying to do is concatenate the pdfs with
pdftk with something like the following
pdftk `ls *.pdf | sort -n` cat output output.pdf
but that doesn't work as my sorting is wrong.