This document discusses handling repetition in programming through control structures like loops. It describes three common loop structures - the for loop, while loop, and until loop. The for loop executes a list of commands for each value in a list. The while loop repeatedly executes commands as long as a condition is true. The until loop repeatedly executes commands until a condition becomes true. Examples are provided for each loop type using shell script code. The document also discusses using functions to organize repetitive code into reusable blocks. Functions allow defining a named subroutine with its own set of commands.

1. Handling Repetition
Presentation Subtitle

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What is Handling Repetition ?
Handling Repetition is control structure also known as looping control structure,Handling Repetition is control structure also known as looping control structure,
is a type of control structure in programming languages that is used to simplify repetitive oris a type of control structure in programming languages that is used to simplify repetitive or
recursive tasks operation.recursive tasks operation.

3. Delete zero sized files in system.Delete zero sized files in system.
3
Code for write a script to delete zero sized files from a given directory
(and all its subdirectories) in Unix / Linux / Ubuntu
Code for write a script to delete zero sized files from a given directory
(and all its subdirectories) in Unix / Linux / Ubuntu

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Script 19
Handling Repetition is control structure also known as looping control structure,Handling Repetition is control structure also known as looping control structure,
is a type of control structure in programming languages that is used to simplify repetitive oris a type of control structure in programming languages that is used to simplify repetitive or
recursive tasks operation.recursive tasks operation.

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Repetitive tasks
1.1. The for loopThe for loop
2.2. The while loopThe while loop
3.3. The until loopThe until loop

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The for loopThe for loop
The for loop is the first of the three shell looping constructs.
This loop allows for specification of a list of values.
A list of commands is executed for each value in the list.

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for loop Syntaxfor loop Syntax

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for loop Examplefor loop Example
$ cat for1.sh
i=1
for day in Mon Tue Wed Thu Fri
do
echo "Weekday $((i++)) : $day"
done
$ ./for1.sh
Weekday 1 : Mon
Weekday 2 : Tue
Weekday 3 : Wed
Weekday 4 : Thu
Weekday 5 : Fri

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The while loopThe while loop
The while construct allows for repetitive execution of a list of commands, as long as the
command controlling the while loop executes successfully (exit status of zero)
The while construct allows for repetitive execution of a list of commands, as long as the
command controlling the while loop executes successfully (exit status of zero)

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The while loopThe while loop

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while loop Syntaxwhile loop Syntax

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while loop Examplewhile loop Example
a=0
while [ $a -lt 10 ]
do
echo $a
a=`expr $a + 1`
done

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The until loopThe until loop

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until loop Syntaxuntil loop Syntax
until <TEST-COMMAND>;
do
CONSEQUENT - COMMANDS;
done

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until loop Exampleuntil loop Example
until [ $DISKFUL -ge "90" ];
do
DATE=`date +%Y%m%d`
HOUR=`date +%H`
mkdir $WEBDIR/"$DATE"
while [ $HOUR -ne "00" ];
do
DESTDIR=$WEBDIR/"$DATE"/"$HOUR"
mkdir "$DESTDIR" mv $PICDIR/*.jpg "$DESTDIR"/
sleep 3600 HOUR=`date +%H`
done

17. Functions in script

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What is Function ?
A function is a subroutine, a code block that implements a set of operations, a "black
box" that performs a specified task. Wherever there is repetitive code, when a task repeats
with only slight variations in procedure, then consider using a function.

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Syntax of Function ?
function function_name {
command...
}
or
function_name () {
command...
}

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Example of Function ?

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Example of Function ?

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