bash - How to redirect the output of a script to a file, but not the error? -

i want append output of wpa_passphrase file if parameters valid, , leave err msg screen otherwise.

i use

wpa_passphrase 1 111 2>&1 >>file wpa_passphrase 1 111111111 2>&1 >>file 

but file still contains msg , screen did not:

passphrase must 8..63 characters 

thanks all

the problem wpa_passphrase writes errors stdout not stderr. code should solve problem:

out=$(wpa_passphrase 1 1111111111) && echo "$out" >> file || echo "$out" 

the code assigns output variable , echos variable file if preceding command successful, otherwise prints output screen.