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Summing Up
We started this chapter with a question. How could we make our sys_info_page script detect if the user had permission to read all the home directories? With our knowl- edge of if, we can solve the problem by adding this code to the report_home_space function:
report_home_space () {
if [[ $(id -u) -eq 0 ]]; then cat <<- _EOF_
<H2>Home Space Utilization (All Users)</H2>
<PRE>$(du -sh /home/*)</PRE>
_EOF_
else
cat <<- _EOF_
<H2>Home Space Utilization ($USER)</H2>
<PRE>$(du -sh $HOME)</PRE>
_EOF_
fi return
}
report_home_space () {
if [[ $(id -u) -eq 0 ]]; then cat <<- _EOF_
<H2>Home Space Utilization (All Users)</H2>
<PRE>$(du -sh /home/*)</PRE>
_EOF_
else
cat <<- _EOF_
<H2>Home Space Utilization ($USER)</H2>
<PRE>$(du -sh $HOME)</PRE>
_EOF_
fi return
}
We evaluate the output of the id command. With the -u option, id outputs the numeric user ID number of the effective user. The superuser is always zero and every other user is a number greater than zero. Knowing this, we can construct two different here docu- ments, one taking advantage of superuser privileges, and the other, restricted to the user’s own home directory.
We are going to take a break from the sys_info_page program, but don’t worry. It will be back. In the meantime, we’ll cover some topics that we’ll need when we resume our work.