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Chapter9

Answers to Evennumbered Exercises

9

1.

2. What are two ways you can execute a shell script when you do not have execute access permission to the file containing the script? Can you execute a shell script if you do not have read access permission?
You can give the name of the file containing the script as an argument to the shell (for example, sh scriptfile, where scriptfile is the name of the file containing the script).
Under bash you can give the following command:
$ . scriptfile

Because the shell must read the commands from the file containing a shell script before it can execute the commands, you must have read permission for the file in order to execute the shell script.
3.

4. Assume that you have made the following assignment:
$ person=jenny

Give the output of each of the following commands:
a. echo $person jenny b. echo '$person'
$person
c. echo "$person" jenny 5.

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6. Assume that the /home/jenny/grants/biblios and /home/jenny/biblios directories exist. For both (a) and (b), give Jenny’s working directory after she executes the sequence of commands given. Explain.
a.
$ pwd
/home/jenny/grants
$ CDPATH=$(pwd)
$ cd
$ cd biblios

After executing the preceding commands, Jenny’s working directory is
/home/jenny/grants/biblios.
When CDPATH is set, cd searches only the directories specified by
CDPATH; cd does not search the working directory unless the working directory is specified in CDPATH (by using a period).
b.
$ pwd
/home/jenny/grants
$ CDPATH=$(pwd)
$ cd $HOME/biblios

After executing the preceding commands, Jenny’s working directory is
/home/jenny/biblios because, when you give cd an absolute pathname as an argument, cd does not use CDPATH.
7.

8. Give the following command:
$ sleep 30 | cat /etc/inittab

Is there any output from sleep? Where does cat get its input from? What has to happen before you get a prompt back?
There