Use Awk to extract substring

You just want to set the field separator as . using the -F option and print the first field:

$ echo aaa0.bbb.ccc | awk -F'.' '{print $1}'
aaa0

Same thing but using cut:

$ echo aaa0.bbb.ccc | cut -d'.' -f1
aaa0

Or with sed:

$ echo aaa0.bbb.ccc | sed 's/[.].*//'
aaa0

Even grep:

$ echo aaa0.bbb.ccc | grep -o '^[^.]*'
aaa0

Or just use cut:

echo aaa0.bbb.ccc | cut -d'.' -f1