C2110 UNIX and Programming 5th lesson -1C2110
UNIX and Programming
Petr Kulhánek
kulhanek@chemi.muni.cz
National Centre for Biomolecular Research, Faculty of Science,
Masaryk University, Kamenice 5, CZ-62500 Brno
5th lesson
Programs vs scripts, algorithms, bash
C2110 UNIX and Programming 5th lesson -2Test
I
C2110 UNIX and Programming 5th lesson -3Test
I
➢ Test through ROPOT in IS
Student - ROPOT - C2110 - Test 1c
Time limit - 20 minutes.
Only one set of questions can be built.
Continuously save your answers.
Evaluation can be done only once.
It is allowed and recommended:
• to test commands in the terminal.
• to search in the manual pages, in your notes and presentations of the
course.
• when in doubt, ask the teacher.
It is not allowed:
• to communicate with another person except the teacher.
(ROPOT = Revision, Opinion Poll and Testing)
C2110 UNIX and Programming 5th lesson -4-
Contents
➢ Programs vs. Scripts
• compiled vs. interpreted languages, examples
➢ Introduction to Programming
• algorithms, algorithm notation, data structures, operations,
input/output operations
➢ Bash
• interactive vs. non-interactive mode, direct and indirect
running of scripts
C2110 UNIX and Programming 5th lesson -5Programs
vs Scripts
C2110 UNIX and Programming 5th lesson -6Programs
vs Scripts
source code
program
input
outputcompilation
script interpreter
input
output
The program is a set of machine
instructions processed directly by the
processor. The program is obtained
through the compilation of the source
code written in a programming language.
Compiled languages:
C/C++
Fortran
The script is a text file containing
commands and control sequences that
are executed by interpreter of the
scripting language.
Scripting languages:
bash
gnuplot
awk
JavaScript
PHP
python
C2110 UNIX and Programming 5th lesson -7What
about JAVA?
There are also various combinations of these two approaches, for example the Java
programming language.
Java bytecode
interpreter
JVM
input
output
source code
compilation
Java Virtual Machine
Java bytecode interpreter
(program compiled for a
given platform - OS and HW)
Java bytecode
(platform independent - OS and HW)
C2110 UNIX and Programming 5th lesson -8Programs
vs Scripts ...
➢ recompilation is not required
➢ possible to create self-executable
code
➢ problematic optimization
➢ slow execution
➢ easy optimization
➢ fast execution
➢ recompilation necessary
➢ not possible to create selfexecutable
code
source code
program
input
outputcompilation
script interpreter
input
output
C2110 UNIX and Programming 5th lesson -9Program
in C
#include <stdio.h>
int main(int argc,char* argv[])
{
printf("This is program in C language!\n");
return(0);
}
Compilation
$ gcc program.c -o program
Source code
Launch of program
$ ./program
compiler of C language name of file with compiled
program
File program must have permission for execution
C2110 UNIX and Programming 5th lesson -10Script
in bash
#!/bin/bash
echo "This is script in Bash interpreter!"
Launch of script
Bash interpreter
File script.bash does not need permission for
execution
Script
$ bash script.bash
C2110 UNIX and Programming 5th lesson -11Exercise
I
1. Create directories called task01 and task02 in your home directory.
2. Save the program.c file into task01 and the skript.bash file into task02. The source of
both files is
/home/KULHANEK/Documents/C2110/Lesson05/programs
3. Compile the source code of a program written in C. Verify that the compiled program
can be executed.
4. What is the size of the file containing the compiled program? Open the resulting file in
a text editor (gedit). What does it contain?
5. Verify functionality of the script skript.bash by executing it.
6. Change functionality of program.c and skript.bash, so they will print different output.
C2110 UNIX and Programming 5th lesson -12Basics
of Programming
https://cs.wikipedia.org/wiki/Algoritmus
C2110 UNIX and Programming 5th lesson -13-
Algorithmization
Problem formulation
Problem analysis
Algorithm
formulation
Program assembly
Program testing
Problem formulation
It is necessary to formulate requirements, specify the input data,
desired results and the accuracy of the solution (for numerical task).
Problem analysis
Verification that the task is feasible for the expected input data. The
most appropriate solution is proposed according to the nature of the
task.
Algorithm formulation
Assembly of unambiguous sequence of operations that have to be
performed in order to properly resolve the task.
Program assembly
Source code of the program in chosen programming language is
created on the basis of the algorithm.
Program testing
Finding syntax errors in the source code and logic errors in design of
the algorithm. Testing program functionality on the specified data.
C2110 UNIX and Programming 5th lesson -14-
Algorithm
Algorithm is the precise manual or procedure for solving given type of problem. The term
algorithm is mostly used in programming, where it describes theoretical principle of
solving the problem (as opposed to the exact procedure in a particular programming
language). In general, algorithm can appear in any other scientific discipline.
Required properties:
▪ Determinism - algorithm must be accurate, exact and unambiguous, i.e. next step is
clearly determined at each point and the same input data must provide the same
results. (Operation of algorithm must not depend on the goodwill of the person or the
characteristics of the machine, where it was implemented).
▪ Generality - the algorithm is not used to solve just one task, but it is solution for whole
group of jobs, which differ only by the input data. Input data can in some range vary.
▪ Finiteness - searched results must be obtained after a finite number of steps, algorithm
must finish after a finite number of steps.
Notation of algorithm:
▪ words
▪ pseudocode
▪ graphic (flowcharts, etc.)
C2110 UNIX and Programming 5th lesson -15-
Flowchart
processing block
input/output block
yes
no
decision making block
terminal (start, end)
Blocks are combined to unambiguously
describe the sequence of operations that
must be executed to correctly solve the
task. Operations or groups of operations to
be executed are written into individual
blocks.
The flowchart is a graphical representation of an algorithm. The flowchart consists of
blocks that are executed in the order given by the direction of flow lines from the
beginning to the end.
Additional blocks exist.
C2110 UNIX and Programming 5th lesson -16-
Examples
I < N
yes
no
write "X"
I=0
N=10
S
E
write "\n"
I=I+1
Flowchart: Word description:
1. Insert value 0 into variable I
2. Insert value 10 into variable N
3. Is the value of the variable I lower than N
YES – Continue with step 4
NO – Continue with step 7
4. Print character X.
5. Increase the value of the variable I by one.
6. Continue to step 3
7. Print end of the line
8. End
C2110 UNIX and Programming 5th lesson -17-
Examples
I < N
yes
no
write "X"
I=0
N=10
E
write "\n"
I=I+1
Algorithm Script in bash
#!/bin/bash
I=0
N=10
while [ $I -lt $N ]; do
echo –n "X"
((I=I+1))
done
echo ""
Result:
$ ./my_script
XXXXXXXXXX
$
S
C2110 UNIX and Programming 5th lesson -18Data
Structures
Data structures are used for storing data. The basic data structures include:
a) variable
b) array
c) record
d) object
Variable is named location in the memory that contains a value. Each variable is of certain
type, which limits possible operations with the variable. Type of the variable can be given
when creating the variable (explicit type) or can be determined only when the variable is
used (implicit type). The variable type affects the way of storing the data in the memory of
a computer.
Examples:
A=“magical phrase"
B=5
C=10.458
D=B+C
E=A+B
text (string)
integer
real number (with floating point)
C2110 UNIX and Programming 5th lesson -19-
Operations
Basic operation:
= assignment
+ sum
- difference
* multiplication
/ division
Logic operation:
== equal
!= not equal
< lower
<= lower or equal
> greater
>= greater or equal
processing block
decision making block
I=0
N=10
I=I+1
F=10*X*X+5*X+1
F=(X+2)*(Y-6)+3
I != N I < N I < N+5
C2110 UNIX and Programming 5th lesson -20-
Input
Input of a program can be an information entered by the user from the terminal,
redirected from a file, or from another program by using pipes.
Basic operations (pseudocode):
read var Read value to variable var
write “Enter value:"
read A
Example:
program will print task for the user and
will expects user’s input, which is then
stored in the variable A.
Input defined in this way reflects the basic options of bash language. Usage of other input
options is not recommend at this stage.
C2110 UNIX and Programming 5th lesson -21-
Output
Output is printed to the terminal. The terminal acts as a printer, which can not take back
an already printed character. In addition, the printer can go to the beginning of the new
line by printing “\n” character to the terminal.
Basic operations (pseudocode):
writestr “string" prints characters (string) specified in quotation
writevar var prints value of the variable var
writestr “Entered value: "
writevar A
writestr "\n"
Example:
Prints text “Entered value" followed by
value of variable A. Cursor will be move on
the new line.
Output defined in this way reflects the basic options of bash language. Usage of other
output options is not recommended at this stage.
C2110 UNIX and Programming 5th lesson -22-
Bash
https://www.gnu.org/software/bash/
C2110 UNIX and Programming 5th lesson -23Bash
– Overview
Unix shell (also command processor) is term of text user interface, which is the
predecessor of the graphical user interface.
Bash is one of Unix shells.
Bash is POSIX shell with a number of extensions. It is designed for operating systems based
on GNU project and can be run on the most Unix-like operating systems. It is used as
implicit command interpreter in systems built on the Linux kernel, as well as in Mac OS X or
Darvin system. It can be used in Microsoft Windows by using Subsystem for Unix
Applications (SUA), or by POSIX emulation using software Cygwin and MSYS.
https://cs.wikipedia.org
http://www.cygwin.com/
C2110 UNIX and Programming 5th lesson -24Interactive
Mode
[kulhanek@wolf ~]$
username
machinename
current directory (~ home directory/home/username)
Prompt – user type/calls ($ user, # superuser, other options %, >)
place for command
Command is executed by pressing Enter.
History: list of previously used commands can be scrolled through by using the arrow keys
up and down. A command from history can be reused or modified to use. History is also
accessible by command history.
Auto completion: command line interpreter can try to complete itemized word by pressing
Tab. It can be used to complete command names, paths and filenames (if first Tab does not
give any output, more options exists and are displayed by repeated press of Tab).
Shell interprets (expands) wild characters and other special characters, before the
command execution. Control structures of the bash language can be also run in the
interactive mode.
Interactive mode is terminated by typing exit.
C2110 UNIX and Programming 5th lesson -25Non-interactive
mode
1) Indirect start
interpreter of the language is run with name of the script as argument
$ bash my_bash_script
Scripts do not have to have set flag x (executable).
2) Direct start
direct launch of script (shell automatically starts the interpreter).
$ chmod u+x my_bash_script
$./my_bash_script
Scripts have to have set flag x (executable) a interpreter is specified in the script.
#!/bin/bash
echo 'This is script in Bash interpreter!'
C2110 UNIX and Programming 5th lesson -26Interpreter
Specification
#!/bin/bash
echo “This is Bash script!"
Bash script
#!/absolute/path/to/script/interpreter
Specification of the interpreter (first line of script):
⚫ If no script interpreter is specified during its direct start, system shell interpreter
(bash) is used.
⚫ Interpreter specified in the script is ignored during indirect start.
⚫ It is recommended to always specify the interpreter in the script, because it is used by
text editors to highlight syntax.
#!/usr/bin/gnuplot
set xrange[0:6]
plot sin(x)
pause -1
Gnuplot script
C2110 UNIX and Programming 5th lesson -27Interpreter
Specification, II
#!/usr/bin/env interpreter
If the absolute path to the interpreter changes (e.g. when using software modules), it is
possible to apply following structure:
Interpreter must be in a directory defined in
system variable PATH.
#!/usr/bin/env bash
echo "This is script in Bash!"
#!/usr/bin/env gnuplot
set xrange[0:6]
plot sin(x)
pause -1
Bash script Gnuplot script
C2110 UNIX and Programming 5th lesson -28Exercise
II
1. Run the bash command in the terminal. What happened? Exit the second session with
the exit command.
2. Find ID of a process, which is responsible for interpretation of the command line (use
the ps command).
3. Terminate the process using the kill command (kill -9 PID, where PID is a process ID).
What happened?
4. Run the script.bash script from the task02 directory directly.
C2110 UNIX and Programming 5th lesson -29-
Conclusions
C2110 UNIX and Programming 5th lesson -30-
Conclusions
➢Program is a binary file directly executed by the processor. Script
is a text file executed by an interpreter.
➢Algorithmization is a way of transforming a task to a description
(algorithm), which can be easily rewritten into a source code of a
programming or scripting language. The basic principle is to
decompose the task into elementary parts and to define
unambiguous procedure of their execution.
➢Bash is a Unix shell that interprets the command line and at the
same time includes support for running scripts.
C2110 UNIX and Programming 5th lesson -31-
Homework
➢ Algorithmization
C2110 UNIX and Programming 5th lesson -32Homework
- Instructions
1. Create flowcharts for the following tasks. In the flowcharts, use only blocks and
operations including input-output, which are mentioned in this presentation.
2. Draw diagrams in an appropriate software:
▪ e.g. program dia (sudo apt-get install dia)
▪ online tools, e.g. www.draw.io
3. Upload the final diagrams into the Homework Vault L05-EN in IS. Use pdf format. The
filename will be in the following format:
SurnameL05x.pdf
where x is the number of the task. Files that will be named in a different fashion, will
not be controlled (automatic changes of name made by IS are allowed).
4. The deadline for submission is November 5, 2018 23:59.
Recommendation: Use decision-making block before processing block.
C2110 UNIX and Programming 5th lesson -33Task
1
Print a square composed from X characters. Length of the square side is entered by user.
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
Ignore the fact, that this is not visually a square.
Number of X characters per line and the number
of lines must be the same.
C2110 UNIX and Programming 5th lesson -34Task
2
Print a triangle composed from X characters in such a way that one leg of the triangle is
placed on the left side and the other on the top. Length of triangle leg is entered by the
user.
X X X X X X X X X X
X X X X X X X X X
X X X X X X X X
X X X X X X X
X X X X X X
X X X X X
X X X X
X X X
X X
X
C2110 UNIX and Programming 5th lesson -35Task
3
Print a triangle composed from X characters in such a way that one leg of the triangle is
placed on the left side and the other on the bottom. Length of triangle leg is entered by
the user.
X
X X
X X X
X X X X
X X X X X
X X X X X X
X X X X X X X
X X X X X X X X
X X X X X X X X X
X X X X X X X X X X
C2110 UNIX and Programming 5th lesson -36Task
4
Print a square outline composed from X characters. Length of the square side is entered by
the user.
X X X X X X X X X X
X X
X X
X X
X X
X X
X X
X X
X X
X X X X X X X X X X
Ignore the fact, that this is not visually a square.
Number of X characters per line and the number
of lines must be the same.
C2110 UNIX and Programming 5th lesson -37Task
5
Print a square outline and its diagonals composed from X characters. Length of the square
side is entered by the user.
X X X X X X X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X X X X X X X
Ignore the fact, that this is not visually a square.
Number of X characters per line and the number
of lines must be the same.