CSI 3336 Computer Systems Exam 2

How to write c style bash function called foo

foo(){

return 1

}

How to write c bash function called foo

foo(){

echo 1

}

What does shift do in bash?

Shifts the $@ to the left ($2 becomes $1 and so on)

What is the scope of variables in bash?

All variables are totally global unless defined as local than it is local to the scope of function it was created in

In c how do you format printing?

%s : string

%d : decimal

%f : float

%lf : long float

%c : char

%5d : width of 5 right justified

%-5d : width of 5 left justified

%5.2 : width 5, precision of 2

What are the different types of FILE *?

stdin

stdout

stderr

What are the standard file descriptors?

0 : std in

1 : std out

2 : std error

How to open a file with stdio, what happens if it fails

fopen("foo.txt", "r") returns NULL if it does not open and sets errno

What are the flags with opening a file with system call interfaces?

O_RDONLY : read only

O_WRONLY : write only

O_RDWR : read/write

O_APPEND : opens and at EOF

How to open a file with system call interfaces, what happens if it fails

fd = open("foo.txt", O_RONLY)

Returns a file descriptor of -1 if fails.

how to read/write from a file with stdio?

FILE* fp = opens file pointer

char ch;

fscanf(fp, "%c", &ch);

fprintf(fp, &ch);

how to read from a file with system call interfaces?

int fd = opens file descriptor

char ch

read(fd, &ch, 1); => returns size of what was read

write(fd, &ch, 1);

What is the return of c call stat?

0 if success -1 if error

how to create a bit field?

struct foo{

char x : 3;

char y : 5;

}

What is the return of getopt and how can it be used?

char opt;

while ( (opt = getopt(argc, argv, "abcd")) != -1){

switch(opt){

case 'a' : ....

case '?' : => case if option is not found

}

}

what is the return of getopt if the option is not found?

ascii number of '?' i.e. 63

Make a Make file with macros for project with objects main, a, b with a default and cleat target.

CFLAGS = -std=gnu89 -Pedantic -Werror

OBJECTS = main.o a.o b.o

mainTarget: $(OBJECTS)

gcc $(CFLAGS) -o mainTarget $(OBJECTS)

CLEAN:

-rm $(OBJECTS) mainTarget

main.o : main.c a.h b.h

a.o: a.c a.h

b.o: b.c b.h

How to make a flag in getopt have a required argument and how do you access that argument?

"a:" => makes the -a flag required to have argument

To get the arg call the "optarg"

What does c fork() return?

returns the pid, and if it is inside the kid process it will be 0, -1 means it failed to fork

What does wait() do, and how to wait for ALL child processes

Pauses the process and resumes when child terminates. Parent gets the child exit status,

while(wait(NULL) > 0);

unformatted

read and leaves it as it was given

formatted

read and changed into an actual # value

formatted examples

«, », printf()

unformatted examples

get, put, read, write, getline

library calls (stdio)

buffered

system calls

not buffered

what does “clean” do

removes object files. Gets rid of all .o files

write bash function that outputs all subdirectories in current directory

for dirs in $(ls)

do

if [[ -d $dirs]]

then

echo $dirs

fi

done

fragment of code that uses a for loop to display all parameters passed to script

for var in $@

do

echo $var

done

fragment of code that uses a while loop to display all parameters passed to script

while [[$1]]

do

echo $1

shift

done

linux library

.so

env variable allows executable to be executed without user providing absolute path

PATH

regex exp that starts with any number (multiple digits followed by colon)

^[0-9]+:

1 liner to copy a file where path to file is specified in file named dirs to current directory. dirs is in current directory

cp $(cat dirs)./

abandon all changes in vim and quit

:q!

argc

number of arguments

what is a race condition

bug where outcome of a program is determined by which thread or process finishes first

what is blocking

waiting until it receives

what is a zombie

child process in which a parent has not called wait() on. Process cannot end until someone takes its exit status