how can i delete all lines in file by using "vi" ?

You can use following in escape mode to delete all lines from a file.

:1,$d

Or, you could enter on line one:

dG

and that would delete to the end of the file.

If you want to delete ALL the lines, don't bother with vi.

$ cat /dev/null > /tmp/the-file-I-want-nothing-in.txt

This will keep you out of vi and delete all the lines.

...Or if you're using ksh, the command

> /tmp/the-file-I-want-nothing-in.txt

will create a null file.

touch a_new_empty_file.txt

will create a null file, or will change the last_access_time on that file.

> the_file_I_want_nothing_in.txt

will both empty a full file or create a null file. -mk

__________________
If it aint broke,
Fix it till it is.

$ echo > file