Practise Bash scripting: variables, conditions, loops, functions, arguments, arrays and safe scripts. Every solution has been run on Ubuntu and shows its real output.
Review first: Your First Bash Script, Variables and Quoting, Conditions with if and case, Loops, Functions, Arguments and Exit Codes, Arrays and String Handling, Writing Safe Scripts
With price=250 and qty=4, print the subtotal and the total after adding a 10 percent tip, as whole numbers.
$(( )) does integer arithmetic.
price=250
qty=4
sub=$((price * qty))
total=$((sub + sub / 10))
echo "Subtotal: $sub"
echo "Total: $total"Subtotal: 1000
Total: 1100Loop from 1 to 4, printing whether each number is even or odd.
(( n % 2 == 0 )).
for n in {1..4}; do
if (( n % 2 == 0 )); then
echo "$n even"
else
echo "$n odd"
fi
done1 odd
2 even
3 odd
4 evenWrite a function kind that prints file, folder or missing for a path. Test it on /etc/hostname, /etc and /nothing.
-f and -d.
kind() {
if [[ -f "$1" ]]; then
echo "file"
elif [[ -d "$1" ]]; then
echo "folder"
else
echo "missing"
fi
}
kind /etc/hostname
kind /etc
kind /nothingfile
folder
missingRename every .jpeg file in the folder to .jpg, and list the folder.
touch one.jpeg two.jpeg${f%.jpeg} removes the old extension.
for f in *.jpeg; do
mv "$f" "${f%.jpeg}.jpg"
done
lsone.jpg
two.jpgRead staff.csv line by line, skip the header, and print name earns salary for people in Pune.
cat > staff.csv <<'EOF'
name,city,department,salary
Asha,Hyderabad,Engineering,90000
Ravi,Pune,Sales,55000
Meena,Hyderabad,Engineering,105000
Karan,Chennai,Support,42000
Divya,Pune,Engineering,88000
Arjun,Hyderabad,Sales,61000
EOFwhile IFS=, read -r ... with tail -n +2.
while IFS=, read -r name city dept salary; do
if [[ "$city" == "Pune" ]]; then
echo "$name earns $salary"
fi
done < <(tail -n +2 staff.csv)Ravi earns 55000
Divya earns 88000Write a function sum that adds up all its arguments. Call it with 5, 10 and 20.
Loop over "$@".
sum() {
local total=0
for n in "$@"; do
total=$((total + n))
done
echo "$total"
}
sum 5 10 2035Write greet.sh, which prints a usage message to stderr and exits with code 2 if it has no argument, and otherwise greets the name given. Test both.
$# holds the number of arguments.
cat > greet.sh <<'EOF'
#!/bin/bash
if [[ $# -lt 1 ]]; then
echo "Usage: $0 <name>" >&2
exit 2
fi
echo "Hello, $1"
EOF
bash greet.sh
echo "Exit code: $?"
bash greet.sh AshaUsage: greet.sh <name>
Exit code: 2
Hello, AshaCount how many times each word appears in red blue red green red, and print the counts sorted by word.
declare -A.
declare -A count
for word in red blue red green red; do
count[$word]=$(( ${count[$word]:-0} + 1 ))
done
for word in "${!count[@]}"; do
echo "$word ${count[$word]}"
done | sortblue 1
green 1
red 3For /var/log/nginx/access.log, print the folder, the file name, and the extension, using parameter expansion only.
${f%/*}, ${f##*/} and ${f##*.}.
f="/var/log/nginx/access.log"
echo "${f%/*}"
echo "${f##*/}"
echo "${f##*.}"/var/log/nginx
access.log
logWrite a function check that takes a percentage, prints ALERT and returns 1 at 90 or above, and otherwise prints OK. Test it with 45 and 93, printing the status each time.
return 1 sets the status.
check() {
if (( $1 >= 90 )); then
echo "ALERT"
return 1
fi
echo "OK"
}
check 45; echo "Status: $?"
check 93; echo "Status: $?"OK
Status: 0
ALERT
Status: 1Write a function retry that runs a command up to 3 times, stopping when it succeeds. Test it with a command that fails twice, by counting attempts in the file tries.
cat > flaky.sh <<'EOF'
#!/bin/bash
n=$(cat tries 2> /dev/null || echo 0)
n=$((n + 1))
echo "$n" > tries
[[ $n -ge 3 ]]
EOFLoop with for i in 1 2 3, and return 0 on success.
retry() {
local i
for i in 1 2 3; do
if "$@"; then
echo "Worked on attempt $i"
return 0
fi
done
echo "Failed"
return 1
}
retry bash flaky.shWorked on attempt 3Write a script with set -euo pipefail that makes a temporary file, removes it with a trap, and fails on purpose. Show that the file is gone afterwards.
trap 'rm -f "$tmp"' EXIT.
cat > job.sh <<'EOF'
#!/usr/bin/env bash
set -euo pipefail
tmp=$(mktemp)
trap 'rm -f "$tmp"' EXIT
echo "$tmp" > where.txt
false
echo "Never printed"
EOF
bash job.sh
echo "Exit code: $?"
[[ -e "$(cat where.txt)" ]] && echo "Still there" || echo "Removed"Exit code: 1
Removed