Errata

There are a couple of (potential) problems with example 4.9.

a.) In the beginning, there's

OIFS="$IFS"
IFS="
"

and then later

IFS=$OLDIFS

which should be

IFS=$OIFS

(on a sidenote, the quotes around $IFS in `OIFS=$IFS` are obsolete)



b.) the line

mkdir -p ${level_dir}{$level}

should be

mkdir -p ${level_dir}${level}



c.) the whole problem with

IFS="
"
for line ...; do
IFS=$OLDIFS
...
IFS="
"

can be avoided by using read instead of a for loop. Here's an approach in awk that handles the situation pretty well:

$ cat foo.awk
#!/usr/bin/env awk -f

BEGIN \
{
FS=":";
passwd = "/etc/master.passwd";
}

/^#/ \
{
next;
}

{
uid = $3;
gid = $4;
if (uid >= 1000 && uid < 5000)
print >> (level_dir 1 passwd);
if (uid >= 5000 && uid < 10000)
print >> (level_dir 2 passwd);
if (gid != 101)
print >> (level_dir 3 passwd);
}

it could be called like this:

$ awk -v level_dir=bar -f foo.awk /etc/passwd;

and would get rid of the whole 'for line in ...' loop



d.) sorting is an expensive operation. If the resulting lists in level_dir should really be sorted, merge-sort teaches us that sorting small lists is less expensive and we should sort them instead.



e.) it's a little strange to have three loops that all loop over the same variables when what they do could easily be combined into a single loop



f.) the lines

mkdir -p ${level_dir}${level}
rm -rf ${level_dir}${level}/*
for dir in /etc /usr/local/etc; do
mkdir -p ${level_dir}${level}/${dir}
done
touch ${level_dir}${level}/etc/master.passwd
chown root:wheel ${level_dir}${level}/etc/master.passwd
chmod 600 ${level_dir}${level}/etc/master.passwd

would be a whole lot more readable this way:

curlev = ${level_dir}${level}
rm -rf ${curlev}
mkdir -p ${curlev}{/etc,/usr/local/etc}

# make sure master.passwd exists and has sane permissions
mpwd = ${curlev}/etc/master.passwd
touch ${mpwd}
chown root:wheel ${mpwd}
chmod 600 ${mpwd}