Dia command line not working
On the Mac, dia (specifically /Applications/Dia.app/Content/Resources/bin/dia) is just a shell script wrapper to the compiled dia-bin binary.  It sets a number of environmental variables, and then finishes by executing Dia as a GUI:

exec "$CWD/dia-bin" --integrated


You can make a copy (e.g. cp -p dia dia-cmd) and edit that last line in dia-cmd to become:

"$CWD/dia-bin" $@


and then you can use it as dia-cmd within the terminal.

Note:  I found that for my locale (en_US.UTF-8), at least, running dia-cmd in the terminal was way too chatty about trying to determine the correct locale, spewing ignorable warnings:

Warning: AppleCollationOrder setting not found, using AppleLocale.
Setting Language: en.UTF8

(process:33043): Gdk-WARNING **: locale not supported by C library

(process:33043): Gtk-WARNING **: Locale not supported by C library.
    Using the fallback 'C' locale.


You can eliminate that by also commenting-out those lines in dia-cmd, and manually forcing the correct locale:

## LANGSTR=`defaults read .GlobalPreferences AppleCollationOrder 2&gt;/dev/null`
## if [ "x$LANGSTR" == "x" ]
## then
##    echo "Warning: AppleCollationOrder setting not found, using AppleLocale." 1&gt;&amp;2
##    LANGSTR=`defaults read .GlobalPreferences AppleLocale 2&gt;/dev/null | \
##            sed 's/_.*//'`
## fi

# NOTE: Have to add ".UTF-8" to the LANG since omitting causes Dia
#       to crash on startup in locale_from_utf8().
## export LANG="$LANGSTR.UTF8"
 export LANG="en_US.UTF-8"
## echo "Setting Language: $LANG" 1&gt;&amp;2


Voila:

MYMACHINE:~ lars$ /Applications/Dia.app/Contents/Resources/bin/dia-cmd -v
Dia version 0.97.2, compiled 18:51:13 Mar 17 2012