Bug#911157: lintian: complain about grepping the passwd/group file instead of using getent

[Rhonda D'Vine <rhonda@debian.org>]

Package: lintian
Severity: wishlist

Dear Maintainer,

 I was prodded by Lamby to file this bugreport. :)  I noticed in a
package (not yet in Debian) that it uses grep on the passwd/group file
directly instead of using getent.  This hinders detecting users stored
in a different database.

 Given that this still seems to exist within Debian packages from a
quick code search, it would be useful to have that reported.
https://sources.debian.org/src/proftpd-dfsg/1.3.5d-1/debian/proftpd-basic.postinst/?hl=28#L28
is an example from our pool, but there are more.

 The package where I stumbled upon this had the code a bit more complex,
I'm unsure how this might be detectable:

#v+
PASSWDFILE=/etc/passwd
GROUPFILE=/etc/group

frruid=`egrep "^frr:" $PASSWDFILE | awk -F ":" '{ print $3 }'`
frrgid=`egrep "^frr:" $GROUPFILE | awk -F ":" '{ print $3 }'`
frrvtygid=`egrep "^frrvty:" $GROUPFILE | awk -F ":" '{ print $3 }'`
#v-

 But for the above example a "grep .* /etc/(passwd|group)" or something
along that lines might be a good starting point.

 Enjoy,
Rhonda
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