>If you can rely on Carriage Returns to be the line seperators:
>?occurs(chr(13),filetostr(yourfilename))+1

Also, if you also wish to count soft returns and ensure the memowidth setting is at the maximum you wish to allow:
?memlines(filetostr(yourfilename))

>
>
>>HI all!!
>>
>>I wonder if someone has an specific technique to get the number of lines from a text file...
>>
>>thanks