vim - vimscript detect piped input -

it easy use vimscript determine if filename specified vim using argc(). there way determine if - flag given specify piped input given vim? doesn't count piped input filename , argc() empty.

edit

thanks wonderful accepted answer below, have way open nerdtree if there no filenames and stndin not being used.

let wmuse_nt = 0 autocmd stdinreadpost * let wmuse_nt = 1 autocmd vimenter * if !argc() && wmuse_nt == 0 | nerdtree | endif 

you use autocmd run before or after vim reads stdin stdinreadpre or stdinreadpost events. copied below.

                                                         stdinreadpost stdinreadpost                   after reading stdin buffer,                                 before executing modelines.  used                                 when "-" argument used when vim                                 started --.                                                         stdinreadpre stdinreadpre                    before reading stdin buffer.                                 used when "-" argument used when                                 vim started --.