Arch Linux

wrong part:
1370 PAC_SYNC_SERVER="$(cat $ANSWER)"
1371 if [ "$PAC_SYNC_SERVER" = "Custom" ]; then
1372 DIALOG --inputbox "Enter the full URL to packages, for example:\nhttp://server.org/archlinux/\$repo/os/i686" 8 65 "http://" 2>$ANSWER || return 1
1373 PAC_SYNC_SERVER="$(cat $ANSWER)"
1374 fi
1375 else
1376 PAC_SYNC_SERVER="${SYNC_URL}"
1377 fi
1378 # comment out all existing mirrors
1379 sed -i -e 's/^Server/#Server/g' "$mirrorlist"
1380 # add our new entry at the end of the file
1381 echo "# Setup-configured entry" >> "$mirrorlist"
1382 echo Server = $PAC_SYNC_SERVER >> "$mirrorlist"
1383 # NOTE: no call to ${EDITOR} for this 'file'

proposed correction, it's propably not 100% fitting to normal setup:
PAC_SYNC_SERVER="$(cat $ANSWER)"
if [ "$PAC_SYNC_SERVER" = "Custom" ]; then
DIALOG --inputbox "Enter the full URL to packages, for example:\nhttp://server.org/archlinux/\$repo/os/$(uname -m)" 8 65 "http://" 2>$ANSWER || return 1
PAC_SYNC_SERVER="$(cat $ANSWER)"
fi
else
PAC_SYNC_SERVER="$(echo ${SYNC_URL} | sed 's/core/\$repo/g')"
fi
# comment out all existing mirrors
sed -i -e 's/^Server/#Server/g' "$mirrorlist"
# add our new entry at the end of the file
echo "# Setup-configured entry" >> "$mirrorlist"
echo Server = $(egrep -o "$PAC_SYNC_SERVER.*" "$mirrorlist") >> "$mirrorlist"