COMP1521 2020T2 Q5 — Processes & syscalls

COMP1521 2020T2 Q5 · 10 marks · C
Topic: Processes & syscalls · Source: https://cgi.cse.unsw.edu.au/~cs1521/26T1/resources/practice_exams.html

Summary: Compare whether two environment-variable values are equal

Write a C program, practice_q5.c ,
which takes two names of environment variables as arguments.
It should print 1
iff both environment variables are set to the same value.
Otherwise,
if the environment variables differ in value,
or either environment variable is not set,
it should print 0 .

The shell command export sets an environment variable to a value;
the shell command unset unsets an environment variable.
In the following example,
export is used to set the environment variables
VAR1 , VAR2 and VAR3 , and
unset is used to ensure environment variables VAR4 and VAR5 are unset.

export VAR1=hello
export VAR2=good-bye
export VAR3=hello
unset VAR4
unset VAR5
./practice_q5 VAR1 VAR2
0
./practice_q5 VAR3 VAR1
1
./practice_q5 VAR2 VAR4
0
./practice_q5 VAR4 VAR5
0

There is no supplied code for this question.

Your program can assume it is always given 2 arguments.

Your program should always print one line of output.
The line of output should contain only 0 or 1.

Your solution must be in C only.

You are not permitted to run external programs.
You are not permitted to use system, popen, posix_spawn, fork or exec.

🤖 Adapted (the online judge has no environment-variable channel): read TWO lines from stdin = the two values. A line <unset> means the variable is unset. Print 1 iff both are set and equal, else 0.

Verified on the sandbox AND cross-checked against an independent oracle.