Hi, i followed David's advise to consider the warnings of shellcheck, to drop the demand for bash, and to check early whether all needed programs are available. xorriso gets now checked for being young enough for the job of replaying the boot related commands as detected with input ISO 1. (1.3.2 in Debian 8 is too old. 1.4.6 in Debian 9 is ok.)
The warnings yielded no real problem fixes but several improvements in regard to general shell code quality. The switch from /bin/bash to /bin/sh was not costly. A printf formatter had to be changed and a use of "type -p" for a message was dropped. An test installation with the resulting ISO succeeded and was able install further packages from all three merged DVD ISOs. (I still could need proposals for further checking the fitness of the ISO.) As before, the script is available at https://dev.lovelyhq.com/libburnia/libisoburn/raw/branch/master/test/merge_debian_isos with https://dev.lovelyhq.com/libburnia/libisoburn/raw/branch/master/test/merge_debian_isos.sig The changes are to see at https://dev.lovelyhq.com/libburnia/libisoburn/commit/34981b1278610d3f31da90f57fdf1378d6012074 Have a nice day :) Thomas