Chapter 5 answers

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← Chapter 5 ChallengesHomeChapter 6: Shell Redirection →

  • Decide whether the following sentence is true or false:
  1. False
  2. False
  3. False
  4. False
  5. True
  6. True
  7. True

  • Write a menu driven script using the select statement to print calories for food items such as pizza, burger, Salad, Pasta etc.

  • Write a shell script that, given a file name as the argument will count vowels, blank spaces, characters, number of line and symbols.
#!/bin/bash
file=$1
v=0
 
if [ $# -ne 1 ]
then
	echo "$0 fileName"
	exit 1
fi
if [ ! -f $file ]
then
	echo "$file not a file"
	exit 2
fi
 
while read -n 1 c
do
  l=$(echo $c | tr [:upper:] [:lower:])
  [[ "$l" == "a" || "$l" == "e" || "$l" == "i" || "$l" == "o" || "$l" == "u" ]] && (( v++ ))
done < $file
 
echo "Vowels : $v"
echo "Characters : $(cat $file | wc -c)"
echo "Blank lines : $(grep  -c '^$' $file)"
echo "Lines : $(cat $file|wc -l )"

  • Write a shell script that, given a file name as the argument will count English language articles such As 'A', 'An' and 'The'.
#!/bin/bash
file=$1
a=0
 
if [ $# -ne 1 ]
then
	echo "$0 fileName"
	exit 1
fi
if [ ! -f $file ]
then
	echo "$file not a file"
	exit 2
fi
 
while read line
do
  l=$(echo $line | tr [:upper:] [:lower:])

for word in $l
do
	[[ $word == "a" || $word == "an" || $word == "the" ]] && ((a++))
done

done < $file
 
echo "articles : $a"

  • Write a shell script that, given a file name as the argument will write the even numbered line to a file with name evenfile and odd numbered lines in a text file called oddfile.
#!/bin/bash
file=$1
counter=0
 
if [ $# -ne 1 ]
then
	echo "$0 fileName"
	exit 1
fi
if [ ! -f $file ]
then
	echo "$file not a file"
	exit 2
fi
 
while read line
do
	((counter++))
	EvenNo=$(( counter%2 ))

	if [ $EvenNo -eq 0 ] 
	then
		echo $line >> evenfile 
	else
		echo $line >> oddfile
	fi

done < $file

  • Write a shell script to monitor Linux server disk space using a while loop. Send an email alert when percentage of used disk space is >= 90%.
#!/bin/bash
ADMIN="me@somewher.com"
# set alert level 90% is default
ALERT=90
df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
do
  #echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
  if [ $usep -ge $ALERT ]; then
    echo "Running out of space \"$partition ($usep%)\" on $(hostname) as on $(date)" |
     mail -s "Alert: Almost out of disk space $usep" $ADMIN
  fi
done

  • Write a shell script to determine if an input number is a palindrome or not. A palindromic number is a number where the digits, with decimal representation usually assumed, are the same read backwards, for example, 58285.
#!/bin/bash
echo -n "Enter number : "
read n
 
# store single digit
sd=0
 
# store number in reverse order
rev=""
 
# store original number
on=$n
 
while [ $n -gt 0 ]
do
    sd=$(( $n % 10 )) # get Remainder
    n=$(( $n / 10 ))  # get next digit
    # store previous number and current digit in reverse
    rev=$( echo ${rev}${sd} )
done
 
if [ $on -eq $rev ];
then
  echo "Number is palindrome"
else
  echo "Number is NOT palindrome"
fi

  • Write a shell program to read a number *such as 123) and find the sum of digits (1+2+3=6).
#!/bin/bash

#store the no
num=$1

#store the value of sum
sum=0
 
if [ $# -ne 1 ]
then
	echo "$0 number"
	exit 1
fi

while [ $num -gt 0 ] 
do
	digit=$(( num%10 ))
	num=$(( num/10 ))
	sum=$(( digit+sum ))
done 

echo "Sum of digits = $sum"

  • Write a shell program to read a number and display reverse the number. For example, 123 should be printed as as 321.
#!/bin/bash

#store the no
num=$1

#store the reverse number
rev=0
 
if [ $# -ne 1 ]
then
	echo "$0 number"
	exit 1
fi

while [ $num -gt 0 ] 
do
	digit=$(( num%10 ))
	num=$(( num/10 ))
	rev=$(( digit + rev*10 ))
done 

echo "Reverse of number = $rev"

  • Write the shell program which produces a report from the output of ls -l in the following format using the for loop statement:
file1
file2
[DIR] test/
Total regular files : 7
Total directories : 4
Total symbolic links : 0
Total size of regular files : 2940
#!/bin/bash

#copying the out of ls -l command to a file
ls -l > /tmp/tmp.tmp

#initilizing values
sum=0
dir=0
file=0
link=0

#reading the file
while read line
do 
	#getting the first character of each line to check the type of file 	
	read -n 1 c <<< $line

	#checking if the file is a directory or not
	if [ $c == "d" ] 
	then
		((dir++))
		echo "[DIR] ${line}/" | cut -d" " --fields="1 9" >> /tmp/dir.tmp

	elif [ $c == "-" ] #true if the file is a regular file
	then
		((file++))
		echo $line | cut -d" " -f8 >> /tmp/file.tmp

	elif [ $c == "l" ]  #true if the file is a symbolic link
	then
		((link++))
	fi
	
	size=$( echo $line | cut -d" " -f5 ) #getting the size of the file
	sum=$(( sum+size )) #adding the size of all the files 
done < /tmp/tmp.tmp

cat /tmp/file.tmp #output the name of all the files
cat /tmp/dir.tmp #output the name of all the directory

echo "Total regular files = $file"
echo "Total directories = $dir"
echo "Total symbolic links = $link"
echo "Total size of regular file = $size"

#removing the temporary files
rm /tmp/file.tmp
rm /tmp/dir.tmp
rm /tmp/tmp.tmp

  • Write a shell script that will count the number of files in each of your sub-directories using the for loop.
#!/bin/bash

START=$HOME
 
# change your directory to command line if passed
# otherwise use home directory
[ $# -eq 1 ] && START=$1 
 
if [ ! -d $START ]
then
	echo "$START not a directory!"
	exit 1
fi
 
# use find command to get all subdirs name in DIRS variable
DIRS=$(find "$START" -type d)
 
# loop thought each dir to get the number of files in each of subdir
for d in $DIRS
do
   [ "$d" != "." -a "$d" != ".." ] &&  echo "$d dirctory has $(ls -l $d | wc -l) files" 
done

  • Write a shell script that accepts two directory names as arguments and deletes those files in the first directory which are similarly named in the second directory.

  • Write a shell script to search for no password entries in /etc/passwd and lock all accounts.

  • Write a shell program to read two numbers and display all the odd numbers between those two numbers.

← Chapter 5 ChallengesHomeChapter 6: Shell Redirection →