If you really want to clear the contents of all the log files in a directory.
@echo off
for %%G in (*.log) do (copy /Y nul "%%G")
Just to show you that it works
H:\logfiles>dir /a-d *.log
Volume in drive H is DATA
Volume Serial Number is D2F3-49FA
Directory of H:\logfiles
01/27/12 12:21 PM 16 logfile1.log
01/27/12 12:21 PM 16 logfile2.log
01/27/12 12:21 PM 16 logfile3.log
3 File(s) 48 bytes
0 Dir(s) 58,354,429,952 bytes free
H:\logfiles>clearlog.bat
1 file(s) copied.
1 file(s) copied.
1 file(s) copied.
H:\logfiles>dir /a-d *.log
Volume in drive H is DATA
Volume Serial Number is D2F3-49FA
Directory of H:\logfiles
01/27/12 12:24 PM 0 logfile1.log
01/27/12 12:24 PM 0 logfile2.log
01/27/12 12:24 PM 0 logfile3.log
3 File(s) 0 bytes
0 Dir(s) 58,354,429,952 bytes free