The easists way is to just pass the --batch switch to portupgrade, if that is the program you use for doing everything.
Set the BATCH environment variable if you just want everything that understands it, to obey. The
handbook and
wikipedia give good overviews of environment variables. Reading the documentation for ports, also explains $BATCH, which basically means, don't ask me questions !!!
The handbooks page noted above also gives examples of setting the environment variable in both Bourne and C style shells --- check your shells manual page for details.
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Thou shalt check the array bounds of all strings (indeed, all arrays), for surely where thou typest ``foo'' someone someday shall type ``supercalifragilisticexpialidocious''.