Which can get gnarly on Windows, depending how you launched Julia. E.g. just launching from the Julia executable:
shell> ls ERROR: could not spawn `ls`: no such file or directory (ENOENT) in _jl_spawn(::String, ::Array{String,1}, ::Ptr{Void}, ::Base.Process, ::RawFD, ::RawFD, ::RawFD) at .\process.jl:321 in #414 at .\process.jl:478 [inlined] in setup_stdio(::Base.##414#415{Cmd,Ptr{Void},Base.Process}, ::Tuple{RawFD,RawFD,RawFD}) at .\process.jl:466 in #spawn#413(::Nullable{Base.ProcessChain}, ::Function, ::Cmd, ::Tuple{RawFD,RawFD,RawFD}, ::Bool, ::Bool) at .\process.jl:477 in run(::Cmd) at .\process.jl:591 in repl_cmd(::Cmd, ::Base.Terminals.TTYTerminal) at .\client.jl:91 julia> (It works fine if launched from Git bash)