CSI 3336 Final - Aars

gdb - steps through program one step at a time

n (next)

A product that can be used to determine and find memory leaks

Valgrind

Create and maintain static libraries

ar (archive)

A single copy of a library loaded into memory

Shared libraries

First call to open returns

3

File descriptor

fd

Function that returns a different value every second

time()

Libraries in Linux are known as archives. What is the typical file extension?

.a

Create directory named 'cs3336' (located back one directory in myClass)

mkdir ../myClasses/cs3336

Print all files named fooxx (f case insensitive, xx - two base 10 digits) to printer ecs312

lpr -P ecs312 [Ff]oo[0-9][0-9]

Find the max value using a bash shell script

#!/bin/bash

maxValue() {

max=$1

shift

for val in "$@"

do

if [[ $val -gt $max ]]; then

max=$val

fi

done

echo $max

}

result=$(maxValue 15 18 32 4 98 1)

echo "Max is: $result"

Write a makefile for project (myprog)

- Must have ability to clean, use at least 1 macro, force gnu89 standard on all compiles

CC = gcc -std=gnu89

OBJ = main.o a.o b.o

myprog: $(OBJ)

$(CC) -o myprog $(OBJ)

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

$(CC) -c main.c

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

$(CC) -c a.c

b.o: b.c b.h

$(CC) -c b.c

clean:

rm -f myprog $(OBJ)

What is a system call?

Fundamental interface between an application and the Linux kernel.

How is a system call similar/different from other functions?

Other functions (wrapper functions) invoke system calls. System calls perform the same functions as library functions, but at a different layer of abstraction.

When would you choose to use a system call versus another function?

When working with file descriptors and pipes, system calls must be used to read and write.

Using only system calls for I/O, write readADigit()

- reads individual digit, give int back to calling function if it exists

#include

int readADigit(int fd) {

char ch;

int result = -1;

if (read(fd, &ch, 1) == 1) {

if (ch >= '0' && ch <= '9') {

result = ch - '0';

}

}

return result;

}

Code fragment that uses getopt() to count number of v options given on command land and prints count

-v option: get increasingly verbose diagnostic output

#include

#include

int main(int argc, char *argv[]) {

int opt;

int vcount = 0;

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

if (opt == 'v') {

vcount++;

}

}

printf("Number of -v options: %d\n", vcount);

return 0;

}

Calls the command pwd and redirect its stderr to a file named errLog

pwd 2> errLog

Variable expansion but not file name expansion

" "

The (1) symbol will be expanded as the path to your current directory.

.

Old internet standard protocol for a remote terminal connection

Telnet (23)

Secure alternate protocol

ssh (22), encrypts communication between server and client

Print the number of lines that the string "Bear" is found in the file pressRelease

grep -c "Bear" pressRelease

Replace all occurrences of "Dwayne Johnson" in a file named pressRelease with "The Rock"

sed 's/Dwayne Johnson/The Rock/g' pressRelease

Vim: moves cursor to beginning of file

gg

Vim: get editor to save copy of current file

:w

Vim: get editor to move cursor to end of current line

$

Regex that matches: catinthehat.txt

grep -E "catinthehat.txt" file_name

Regex that matches bears (first letter case insensitive)

grep -E "[Bb]ears" file_name

Shell Expansions: "file" followed by any single char followed by ".txt"

file?.txt

Shell Expansions: all files located in user SMITHB's home directory ending in ".sh"

~SMITHB/*.sh

Shell Expansions: files named "foo" with the first character case insensitive

[Ff]oo

Write to a stream (overwrite)

>

Write to a stream (append)

>>

Developers of C

Denis Ritchie, Brian Kernighan

KISS Principle

Keep it Small and Simple

Good for quick and simple development

shell

C shell

csh

Bash spawns new shell, executes given command, then returns result. (T/F)

True

Bash built-ins run on the original bash, and as a result, is faster and more efficient. (T/F)

True

Do not suppress variable expansion. Suppress shell expansion.

" "

Suppress everything

' '

``Command substitution

- Identical to $(_)

``

Standard in

0

Standard out

1

Standard error

2

Universal trash can in Linux

/dev/null

kills precess specified by pid

kill

grabs all processes related to a specified user

ps -ef | grep user_name

returns first 10 lines

head

returns first num lines

head -num

returns last 10 lines

tail

returns last num lines

tail -num

takes stdout for the first process and uses it as stdin for another process

pipe

allows every instance of the shell to have access to the variable

export

In Bash, 0 is considered true (T/F)

True

global regular expression print

grep

special command (substitution in ed)

- manipulates strings, but by default, does not modify files

sed

Remove all instances of 'TX', replace with Texas

sed 's/TX/Texas/g' file_name

change in place

sed: i

character class

[...] (file name expansion)

range of a number of occurrences (at least n, at most m)

{n, m}

exactly n occurrences

{n}

at least n occurences

{n, }

at most m occurrences

{ ,m}

or

|

escape

\

Shebang line

#!/usr/bin/bash

- indicates what interprets the file

Read, write, executable permissions

- 3 sets of octal numbers

- chmod

-rwxrwxrwx

You must give file executable permissions OR (1)

1. explicitly give it bash when executing

ex. $bash ./hw.sh

Substrings in bash

echo ${foo: starting point: num of char}

Use $(( )) for simple arithmetic and let for unary operations. (T/F)

True

Test

[ ]

[[ ]]

String comparisons

= equivalence

!= not equal

-n not null

-z is null

Number comparison

-eq

-ne

-lt

-gt

-le

-ge

File tests

-d: is a directory

-e: does it exist

-f: regular file

if

if [[ test ]]

then

# stuff

fi

if-elif-else

if [[ test ]]

then

# stuff

elif [[ test ]]

then

# stuff

else

#stuff

fi

case

case val in

pattern1)

# stuff

;;

pattern2)

# stuff

;;

pattern3)

# stuff

;;

esac

for

for var in $set

do

# stuff

done

while

while condition

do

body

done

shifts all items in command line/positional parameters

- allows for reuse of $1

shift

until

until condition

do

body

done

shell suppression

../

Functions in bash

function()

{

body

}

Returning from a function (bash)

1. use of return command (returns an integer, stored in $?)

2. returning as we know it (using echo)

C is a (1) of C++

1. subset

Compile in gnu89 standard

gcc -std=gnu89 file_name -o executable_name

Analogous to new and delete

malloc and free

variables which hold addresses

pointers

printf

%i - integer

%d - decimal

%c - character

%s - string

%f - float

%g - double

%lf - long float

%5d - set width of 5, double, right justified

%-5d - set width of 5, double, left justified

%05d - zeroes leading number

%8.2f - 8 columns, 2 decimals

Interfacing directly with OS via System Call

1. Process control

2. File management

3. Device management

4. Information management

5. Communication

Electric fence

If memory is used incorrectly, segmentation fault

User Space

User Applications, GNU C libraries, Shell

Kernel Space

System calls interface -> device drivers

Hardware Space

Hardware

System-wide error variable

Errno

read()

read(int, void *buffer, size)

write()

write(int, void* buffer, size)

open()

open(char *name, int flags)