Forum OpenACS Q&A: Re: Can't exec a command in tcl page
exec libreoffice --headless --convert-to xls /tmp/fileBXXCcF.xls /tmp/fileBXXCcF.csv
Same error though.
We had this problem with many commands, where the output of the command causes Tcl exec to think the command has failed when it was fine.
We catch the exec and look for specific error responses in the output as necessary.
Many sites I have worked on used a modified exec replacement that took care of the catch automatically.
A longer discussion is e.g. here: http://wiki.tcl.tk/1039