CH:23 Scripting

Question 1

Where user profile scripts run

Answer 1

and init scripts are run when a daemon is stopped or started

Question 2

Why system administrators also need basic knowledge of scripting

Answer 2

to understand how their servers and their applications are started, updated, upgraded, patched, maintained, configured and removed, and also to understand how a user environment is built

Question 3

Output Hello world

Answer 3

$echo Hello world

Question 4

How to make printing hello world executable

Answer 4

1. $ echo echo Hello World > hello_world
2. $ chmod +x hello_world
3. $ ./hello_world

Question 5

she-bang ?

Answer 5

!

aka (sha-bang)
————————————————————————–
Used to :
To instruct a shell to run your script in a certain shell
————————————————————————-
#!/bin/bash
echo -n hello
-> this wiill run in a bash Shell

echo -n hello
-> this wiill run in a Korn Shell

Question 6

Comment ?

Answer 6

# this is a comment line
e.g 

```script
#!/bin/bash
#
# Hello World Script
#
echo Hello world
~~~

Question 7

Variables ?

Answer 7

#!/bin/bash 
#
# simple variable in script 
#
var1=4
echo var1 = $var1

variables do not survive the end of the script cuz scripts runs on their own shell

Question 8

forcing a script to run in the same script is called

Answer 8

Sourcing a script 
---------------------------------------------------------------------------
paul@RHEL4a ~]$ source ./vars 
var1 = 4
[paul@RHEL4a ~]$ echo $var1 
4
[paul@RHEL4a ~]$

----- the bellow is identical to the above one
[paul@RHEL4a ~]$ . ./vars
 var1 = 4
[paul@RHEL4a ~]$ echo $var1 
4
[paul@RHEL4a ~]$

Question 9

how to run a script in a sperate shell

Answer 9

by typing bash with name of the scripts as parameters

$ bash runme

Question 10

hash +x ?

Answer 10

paul@debian6~/test$ bash -x runme
+ var4=42
+ echo 42
42

paul@debian6~/test$ cat runme 
# the runme script 
var4=42 
echo $var4

paul@debian6~/test$

Question 11

setuid root spoofing

& how to improve security

Answer 11

is rare but possible attack

to improve security add – after the #!/bin/bash

#!/bin/bash -
or
#!/bin/bash --

Question 12

Any arguments after the – are treated as .

Answer 12

filenames and arguments. An argument of - is equivalent to –