Jupyter notebook - Couldn't find program: 'bash'

Did you try what the error message said to try?

i.e. '%%bash' instead of '%bash'

This page seems to indicate that you're going to want two percent signs to utilize the bash script magic.

Edit. Tailored answer to no longer be to specific errawr message. When I run %lsmagic I get the following:

%lsmagic

Available line magics:
%alias  %alias_magic  %autocall  %automagic  %autosave  %bookmark  %cd %clear  %cls  %colors  %config  %connect_info  %copy  %ddir  %debug  
%dhist  %dirs  %doctest_mode  %echo  %ed  %edit  %env  %gui  %hist  
%history  %install_default_config  %install_ext  %install_profiles %killbgscripts  %ldir  
%less  %load  %load_ext  %loadpy  %logoff  %logon  %logstart  %logstate  %logstop  %ls  %lsmagic  %macro  %magic  
%matplotlib  %mkdir  %more  %notebook  %page  %pastebin  %pdb  %pdef  %pdoc  %pfile  %pinfo  %pinfo2 
%popd  %pprint  %precision  
%profile  %prun  %psearch  %psource  %pushd  %pwd  %pycat  %pylab  %qtconsole  %quickref  %recall  %rehashx 
%reload_ext  %ren  %rep  %rerun  %reset  %reset_selective  %rmdir  %run  %save  %sc  %set_env  %store  %sx  
%system  %tb  %time  %timeit  %unalias  %unload_ext  %who  %who_ls  %whos  %xdel  %xmode

Available cell magics:
%%!  %%HTML  %%SVG  %%bash  %%capture  %%cmd  %%debug  %%file  %%html  %%javascript  
%%latex  %%perl  %%prun  %%pypy  %%python  %%python2  %%python3  %%ruby  %%script  %%sh  %%svg  %%sx  %%system  
%%time  %%timeit  %%writefile

Automagic is ON, % prefix IS NOT needed for line magics.

The following command works:

%%cmd
dir

buruzaemon nailed it.