Mock Exam - CIS342 2017 Spring

Basic bash commands

Which command can be used to find out how a specific command works, including its arguments?
- A. help
- B. man
- C. where
- D. which
Answer: B. The "man" command is used to find out how to use a command.
What permissions does the following command assigns to file "foo"? chmod 756 foo

Answer: 756 translates to 111 101 110, meaning the full (read, write, and execute) permissions for user, read and execute permissions for group, and read and write permissions for all other people.
Write a command to give rw-rwx--x permissions to file "foo".

Answer: the given permissions translate to 671. This can be done using chmod 671 foo.

Write a bash script to get 2 integers as parameters and print "Ok" if the first parameter is larger that the second one.

Answer:
```
#!/bin/bash
if [ $1 -lt $2 ]; then
	echo Ok
fi
```
What should you do to have access to a variable in all consoles?

Answer: Use export command to make it an environment variable.
Write a bash script to get a path to a directory as parameter and copy all the files inside it to the user's home directory.
- Hint: Symbol ~ refers to home director.
Answer:
```
#!/bin/bash
cp -r $1 ~
```

Consider running grep with ^[1-5].[7-9] regular expression. Which of the following matches? Select all that apply:
- A. 12345
- B. 56789
- C. 87761 2889
- D. 777771827
- E. 2871765
- F. 119991
Answer: BEF
Write a command to find all lines of all files under user's home directory recursively that contains a digit between 5-7 in their names. Ex: file51 matches but file12 does not.

Answer: find ~ -name "*[5-7]*"
You want to list all the files under the root directory but the output is too long and does not fit into your terminal. How do you handle this?

Answer: Use the more command. ls / | more
Write a bash script to get the name of a process (Ex. firefox) and print out the pid for it.

Answer:
```
#!/bin/bash
ps aux | grep $1
```
You are using vim for editing a file. How can you go back to the console without the need to save the file and close vim?

Answer: press Ctrl+Z keys.
Write a bash script named "mymv" that does the same thing as command "mv". You should not use "mv" in your script.

Answer:
```
#!/bin/bash
cp $1 $2
rm $1
```
Use wc and ps aux commands to print number of current running processes.
- Hint: wc -l foo is counting the number of lines in a file foo
Answer: ps aux | wc -l

In the compilation process, describe the functionality of a linker?

Answer: A linker merges the object files into a single executable file.
What is the difference between next and continue commands in gdb?

Answer: next goes to the next line but continue goes to the next breakpoint.
Write the following compilation stages in correct order: linking, preprocessing, assembling, compilation

Answer: preprocessing->compilation->assembling->linking
Write a makefile with two targets. One for compiling foo.c to binary foo.out linking a library file with name "libbar.a". Another target for removing the compiled binary files and cleaning up.

Answer: gcc -o foo.out foo.c -L. -lbar

Given a C program file hello.c, write down the commands that convert the file to the following: 1) an assembly file hello.s, 2) a relocatable object file hello.o, 3) an executable object file a.out.

Answer:
- 1. gcc -S hello.c
- 1. gcc -c hello.c
- 1. gcc hello.c
Where is global variable defined?
- A. outside any function
- B. inside main function
- C. inside a function that is not main.
Answer: A
Write down the gdb command to examine stack?

Answer: bt or backtrace
[True/False] CPU has a register pointing to the memory location of the instruction currently being executed.

Answer: True
[True/False] CPU supports instructions to move data from memory.

Answer: True
How do you allocate memory space to store exactly 3 integers. What happens if we copy more integers to the allocated memory?

Answer: int a=malloc(sizeof(int)*3); and the error is segmentation fault
What error does the following program generate? Why?
```
    #include<stdio.h>
    #include<stdlib.h> 
    int main()
    {
         int *ptr;
         *ptr = 10;
         printf("%d\n",*ptr);
         return 0;
    }
```
Answer: This may cause segmentation fault. Because the program access to low memory address 10 which is (usually in kernel space) and is inaccessible to user-space program.