How can I pack a .tps file using the command line client?

Yes, simply pass the .tps file name as a command-line parameter:

TexturePacker sheet.tps

You can also override settings from the .tps file with additional parameters:

TexturePacker sheet.tps --scale 0.5 --sheet small.png --data small.json

Alternatively, you can use the .tps file as a configuration template and specify input sprites via the command line:

TexturePacker config.tps sprites1/ --sheet sheet1.png --data sheet1.json
TexturePacker config.tps sprites2/ --sheet sheet2.png --data sheet2.json