change character in the passwd file

[OldSchool]

While some of the GNU utilities have the ability to do "in-place" changes (as does perl, i believe) that doesn't work for awk that I know of. One liner like:

awk -f awk.scr /etc/passwd > (temp_file); cp (temp_file) /etc/password


Should get what you want

[OldSchool]

or something like:

cp /etc/passwd (tempfile); awk -f awk.scr (tempfile) > /etc/passwd

[Jocelyn Dinel]

unfortunately, the result is good but not replace directly in the file, only put the line where the :: is find

[Dennis Handly]

>the result is good but only put the line where the :: is found

Try this:
awk -F: '
{
if ($2 == "")
$2 = ",.."
print $0
}' /etc/passwd > (temp file here)

[OldSchool]

I told you...."will find any lines with :: after the login name"

It does nothing with the lines that don't match.

Dennis's version should handle that case as well, by changing the second field if required, and always printing each line.....

That may (or may not be) *exactly* what you need either, but they are places for you to start from....