You would have to emit newline characters in the string you submit to system(), as MATLAB is not able to construct multi-line quoted strings the way that a shell is.
If you want bash specifically, you need to invoke it by name. The shell used by system() is the $SHELL of the environment, which is not certain to be bash. On the other hand, you should be able to take advantage of the #! magic number that is recognized by unix exec*() calls, by coding the first line of path/ish as
and then no matter which shell is your default shell, bash would be invoked to handle path/ish
sysstr = sprintf('path/ish -file placeholder -mode text <<XXX\na...\nb...\n3...\nect ...\nXXX');