C2110 UNIX and Programming
9th lesson Bash - Completion (Almost)
Petr Kulhánek
kulhanek@chemi.muni.cz
National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-62500 Brno
UNIX and programming 9th lesson
Homeworks
Instructions:
1. Listed tasks are for advanced students.
2. The goal of the tasks is to develop your ability to solve problems that are seemingly unsolvable from the point of available options and resources. In case of bash language, this involves mainly the possibility to work only with integer arithmetic and limited way of rendering into the terminal
Tasks:
1. Draw a circle using character "X". The radius of the circle is entered by the user after starting of the script.
2. Draw a circle outline using character "X". The radius of the circle is entered by the user after starting of the script
UNIX and programming 9th lesson
Contents
> Command test
• comparing integers and strings
> Loops
• for vs while, for in, pipes and redirection
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Command test, integers
The test command is used to compare values and to test types of files and directories (man bash, man test). If the test passes successfully, the return value of the command is set to 0 (true).
Integer comparison:
test number1 operator number2
Operator:
-eq equal to
-ne not equal to
-It less than
-le less than or equal to
-gt greater than
-ge greater than or equal to
Additional information: man bash, man test
Alternative notation:
must be spaces
[[ number1 operator number2 ]]
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Command test, strings
Comparison of strings
test stringl operator string2 [[ stringl operator string2 ]]
Operator:
== strings are identical (= also can be used) !=        strings are different
Testing strings
test operator stringl [[ operator stringl ]]
Operator:
-n tests whether the string has not zero length
-z tests whether the string has zero length
-f tests whether the string has name of an existing file
-d tests whether the string has name of an existing directory
UNIX and programming 9th lesson
Command test, logical operators
Logical operators:
| |       logical or &&      logical and ! negation
• Logical operators can be used to create more complex conditions.
• If we do not know priority of the operators, we should use parentheses.
• Bash uses lazy evaluation of conditions, which is based on evaluating only the component of the logical condition that must be evaluated to determine the logical value of the whole condition.
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Command test, examples
[[   (I -ge 5)   &&  (I -le 10)   ] ]
Is the value of the variable I in the range <5;10>?
[[   (I -It 5)||(I -gt 10)   ]]  or  [[   ! ((I -ge 5)&& (I -le 10))   ]]
Is the value of the variable I out of the range <5;10>? [ [ I -ne 0 ]]
Is the value of the variable I different than zero? [[  "$A" == "test" ]]
Does the variable contain string "test"? [ [  "$A"  != "test" ]]
Does the variable contain different string than string "test" [ [ -z "$A" ] ]
Does the variable contain an empty string? [[  -f "$NAME"  ]]
Is there a file with same name as value of NAME? [ [   !   (-d "$NAME")   ] ]
Is there no directory with name as the value of NAME?
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Exercise I
1. Write a script that will ask the user to gradually enter two numbers. Then, it will print quotient of the two numbers. Treat a possible error of division by zero.
2. Write a script that will create a directory, name of directory is entered by the user after staring the script. Treat the error situation caused by already existing directory.
3. Write a script that asks you to enter an integer. The script will then test whether this is indeed an integer.
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Loops: FOR
Loop is a control structure that repeatedly performs a series of commands. Both repeating and exit from the loop is managed by condition.
if the condition is true, commandl and It is executed before starting the ^ . .
...... ° others commands are executed.
loop (counter initialization)
Compact notation:
for((initialization/condition/change)); do commandl
•   • •
done
The counter is updated after the execution of commands.
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FOR loop and flowchart
for((I = 0;  I < N;  I = I + 1)); do echo $1
done
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Loop: FORvs WHILE
if the condition is true, executes commands in the do/done block
performed before start of the loop (counter initialization)
In addition to cnange of the counter at the end of loop, it is possible to execute other changes in the body of the loop. This is not recommended because it reduces code readability.
►1=1			
while	[[ $1 -le	10	] ] ; do
	echo $1		
	((1=1+	1	))
done			
Update counter after the execution of commands
Counter update can be done anywhere in the body of loop (even at multiple locations).
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Prints numbers from 1 to 10
Prints numbers from 10 to 1
for((1=1;I <= 10;I++)); do echo $1
done
Variable I is counter.
Initialization is governed by rather free rules because the expression is in (()) block.
Change:
Possible interpretation of the all mathematical expression that can be interpreted within (( )) block, e.g.: ++ value is increased by one --  value is decreased by one others ...
for((1=10;I >= 1;I—)); do echo $1
done
Condition:
Following comparison operators can be used:
I =	not equal to
——	equal to
1 <	less
I <=	less then or equal to
1 >	greater then
! >=	greater then or equal to
can be used only with integers in (())
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FOR loop, change of counter
If the variable can be interpreted as integer, following arithmetic operators can be used:
++   variable value incrementated by one
A++
variable value decrementated by one A—
+     sums up two values
A = 5 + 6 A = A + 1
subtracts two values
A = 5 - 6 A = A - 1
*      multiplies two values
A = 5 * 6 A = A * 1
/     divides two values (integer division)
A = 5 / 6 A = A / 1
A=A+3
+=   increases var/able by value
A += 3 A += B
-=   decreases variable by value
A -= 3 A -= B
*=   multiplies variable by value
A *= 3 A *= B
/=   divides variable by value
A/=3 A /= B
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Nested loops
Loops can be freely nested,
Outer loop
for((1=1;I <= 10;!++)); do *		
	for((J=l;J<= 10;J++)); do	
	echo "$I $J"	
	done	
done		
Inner loop
counter of outer loop can affect behavior of inner loop
for((1=1;I <= 10;!++));
for((J=l;J <=	); do
echo "$I	$J"
done	
done
The level of nesting is not limited. For loop can be combined with other loops (while, until, for in) or conditions.
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Exercise II
1. Write bash scripts for Task 1 and 2. Use for loops instead of while loops. Size of plotted shape is given as the first argument of the script. The script will tests if the entered number of arguments is correct and if the first argument is an integer greater than zero.
2. Edit the task 1, that the rectangle is printed into the terminal. The size should be entered interactively.
UNIX and programming 9th lesson
Taskl
Print a square composed from X characters to the terminal. Side length of the square 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	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
Please ignore the fact, that it is not visually a square. Number of X characters per line and the number of lines must be the same.
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Task 2
Print a triangle composed from X characters to the terminal. Legs of triangle are placed at left and top of the triangle. Leg length of the triangle 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 XXX
X X X
X X X X X X X X X XXX X X X
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Loop FOR ... IN ...
Commands in the block do/done (commandl, ...) are executed for each element in the list LIST. In the given run of the loop, variable VAR includes current element from the list LIST
for VAR in LIST do
commandl $VAR
•   • •
done
Compact notation:
for VAR in LIST; do commandl $VAR
•  • •
done
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Loop FOR ... IN lists
for A in a	b c; do
echo	$A
done	
Loops will run three times, characters a, b, c are printed, one character in each run of cycle.
It is appropriate to create the list of items algorithmically (using the commands listed in graves - reverse apostrophes).
for A in xls *.epsx; do ./process_file $A
done
for A in x seq 1	0.25	10x; do
printf "%8	.3f\n	" $A
done		
Command process_file is executed for every file with suffix eps, which is in the current directory.
Creates real numbers in the range of 1 to 10 with an increment of 0.25. The numbers will be printed with an accuracy of three decimal places aligned right with 8 character length. Documentation: man seq
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Redirection and pipes
Read file line by line:
pipe
while read A; do command2
•   • •
done < file.txt
Redirection to file:
for((1=1;I <= 10;I++)); do
echo $1 done > file.txt
redirection
Output of all commands in the loop is redirected to file.txt.
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Redirection and pipes - examples
for((1=1;I <= 10;I++)); do
echo $1 done > file.txt
for((1=1;I <= 10;I++)); do echo $1
printf "N=%10d\n" $1 done > file.txt
Same functionality
rm -f file	. txt
for((1=1;I	<= 10;I++)); do
echo	$1 » file.txt
done	
Different functionality
rm -f file.txt
for((1=1;I <= 10;I++)); do echo $1 » file.txt printf "N=%10d\n" $1
done
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Exercise III
1. Edit the scripts from the previous exercise in such a way that size of the shapes would be read from standard input and the resulting shape will be printed to a file, the name of this file is entered to standard input by user
2. Write a script that prints real numbers in the range from -10 to 10 with an increment of 0.5. Numbers will be printed including the sign, right-aligned, values will be 10 characters long and with precision one decimal point.
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Ho me works
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Homework I
Explain different behavior of the following scripts. Data.txt file contains five lines.
#!/bin/bash 1 = 0
cat data.txt   |  while read A; do !=$( ($1 + 1) )
done
echo $1
prints number 0
#!/bin/bash 1 = 0
while read A; do
!=$( ($1 + 1) )
done < data.txt echo $1----1
print number 5
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Homework II
File rst.out (wolf.ncbr.munixz:/home/kulhanek/Documents/C2110/Lesson09/rst.out) contains the results of molecular dynamics simulation. Your task is to extract the temperature dependence of the simulated system on time from the file, you will save these data to file temp.out, which will contain two columns. First column will be time and second column will be temperature.
time
temperature
NSTEP =
Etot
BOND
1-4 NB = EELEC =
500
TIME (PS)
942.6248 51.3204 17.7099
■494 .7423
EKtot ANGLE 1-4 EEL EGB
0.500    TEMP(K) 151.0990 292.3619 981.4071 -164.7991
288.02 PRESS
EPtot DIHED VDWAALS RESTRAINT
0.0
791.5258 176.5980 -68.3301 0.1822
EAMBER (non-restraint)
791.3436
Caution: It is forbidden to use commands grep, awk, and also their variants in the script. To solve the task use commands read and while.
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Selfstudy
functions - for advanced students
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Functions - definition
Function is a structure that allows to group part of the code so that it can be easily used on multiple locations of the script. Functions result in clean and readable code when some tasks are repeated.
Definition:
function name () commandl command2
function name{ commandl command2
name() {
commandl command2
V
alternative notation
Arguments of the function are not declared, therefore there is no control of the number of the given arguments, no type control, and functions can not be overloaded. Given arguments are available via special variables #, 1-9, *. The functions are executed as an existing command. Variables in the function are global (it can be changed by using the keyword local).
Documantation: man bash, sekce FUNCTIONS.
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Function - use
# print line - the length is	in	the first argument
function print line  () {		
N=$l		
for((*=l;J <= N;J++));	do	
e\ho -n " X"		
done \		
echo "" \		
# use function \		
print line 10      # Rrint line	10	characters long
print line    5^v # pVint line	5	characters long
Value of the argument is available via special variable 1
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Exercise
1. Write a script that will print the square, and triangle (similar to task 1 and 2) for one specified length one after another to the terminal. Identify the part that is repeated and rewrite it using function.
X X X X
X X X X
X X X X
X X X X
X X X X XXX X X X
Please ignore the fact, that it is not visually a square. Number of X characters per line and the number of lines must be the same.
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