# note: under sh prompt
$ x=$(date +%d%m%y)
$ echo $x
251218

# another way is use back single quote `
# `` can replace $()
$ y=`date +%d%m%y`                                                                                                     
$ echo $y                                                                                                              
251218  

# using command /bin/date
touch file.`date +%m%d%y`.txt