Portable scripting (POSIX compliance) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a POSIX-compliant shell script snippet

What is the output of this POSIX-compliant shell script snippet?

Bash Scripting

count=0
for file in *; do
  case "$file" in
    *.sh) count=$((count + 1)) ;;
  esac
done
echo "$count"

A Number of files ending with .sh in the current directory

B Always outputs 0

C Total number of files in the current directory

D Syntax error due to missing semicolon

💡 Hint

Look at the pattern matching inside the case statement and the variable increment.

The script loops over all files in the current directory and increments count only for files ending with .sh. The echo prints that count.

📝 Syntax

intermediate

Identify the syntax error in this POSIX shell script

Which option correctly identifies the syntax error in this POSIX shell script snippet?

Bash Scripting

if [ "$var" = "value" ]
then
  echo "Match"
else
  echo "No match"
fi

A Missing spaces around the = operator inside [ ]

B Missing then keyword after the if condition

C No syntax error; script is valid POSIX shell

D Missing closing bracket ] in the if condition

💡 Hint

Check spacing and keywords carefully in POSIX shell if statements.

The script uses correct spacing around = inside [ ] and includes then and fi keywords properly.

🔧 Debug

advanced

Why does this POSIX shell script fail to assign variable correctly?

Consider this POSIX shell snippet: var=$(echo "Hello World" | awk '{print $2}') echo "$var" Why might this fail on some POSIX systems?

Bash Scripting

var=$(echo "Hello World" | awk '{print $2}')
echo "$var"

A The command substitution syntax $(...) is not POSIX compliant

B Some POSIX systems do not have awk installed by default

C The single quotes inside awk cause syntax errors in POSIX shell

D The echo command is not POSIX compliant

💡 Hint

Consider the availability of external commands on minimal POSIX systems.

While the syntax is POSIX compliant, some minimal POSIX systems might not have awk installed, causing the command to fail.

🧠 Conceptual

advanced

Which command is most portable for reading a file line by line in POSIX shell?

You want to read a file line by line in a POSIX-compliant shell script. Which command is the most portable and reliable?

A while IFS= read -r line; do echo "$line"; done < file.txt

B cat file.txt | while read line; do echo "$line"; done

C while read -r line; do echo "$line"; done < file.txt

D for line in $(cat file.txt); do echo "$line"; done

💡 Hint

Consider how to preserve leading/trailing spaces and backslashes in lines.

Option A uses IFS= and read -r to prevent trimming spaces and backslash interpretation, making it the most portable and reliable POSIX method.

🚀 Application

expert

Predict the output of this POSIX shell script with parameter expansion

What is the output of this POSIX shell script snippet? filename="archive.tar.gz" echo "${filename%.tar.gz}"

Bash Scripting

filename="archive.tar.gz"
echo "${filename%.tar.gz}"

A archive.tar

B archive.tar.gz

C Syntax error due to unsupported parameter expansion

D archive

💡 Hint

The % operator in parameter expansion removes the shortest matching suffix.

The expression ${filename%.tar.gz} removes the suffix .tar.gz from the variable, resulting in 'archive'.