Push a ROM to Galaxy S3 (d2att) while in TWRP/CWM?
First of all, do a nandroid backup to save the current state of the phone.

Get a ROM that can be flashed via recovery (usually .zip, not .img or .tar.img), then just execute:

adb shell mount /sdcard
adb push &lt;romname.zip&gt; /sdcard


If the first option to mount the sdcard fails, you can manually mount if from recovery. Also sdcard path might vary from ROM or recovery.

Once the ROM is uploaded to the phone, you can then use the recovery option to install it.

If you're comming from a different ROM, be sure to wipe /system, /data and /cache.