Implement a Small UNIX Shell

Implement a Small UNIX Shell

Overview and Goal

The goal of this task is to write a simple but functional UNIX shell in C. It

must:

Print a shell prompt ($)

Read multiple commands from standard input and execute them

Support shell variables and expansion

Support the variable $? to print out the return code of the last program

Run programs in the background if desired

Support redirection of standard input, output and error

Support the pipeline operator (|)

See expected output below for details.

Important Notes

Executing any real shell (e.g. /bin/bash) through exec(), popen() or

any other means is not a valid solution. All of the functionality must be

implemented by yourself in shell.c!

Do not use isatty() to check if your shell is running in a terminal (e.g.

to display a prompt only in this case). The CI environment is not using a

terminal.

It is recommended to use fflush() to flush the output streams (otherwise,

e.g. CI tests may not work properly)

Expected Output

Print a shell prompt ($) when ready

...

$

Read multiple commands from standard input and execute them

$ echo Hello

Hello

$ expr 1 + 3

4

Support shell variables and expansion

$ A=5

$ echo $A

5

$ echo ${A}BC

5BC

$ A=$A$A

echo $A

55

Support checking the return code of the last program using $?

$ true

$ echo $?

0

$ false

$ echo $?

1

Support running programs in the background with &

$ firefox &

$

After this, Firefox should be running and the shell accepting commands again.

Support redirection of stdin, stdout and stderr with >, < and 2>

$ echo Hello > [login to view URL]

$ cat - < [login to view URL]

Hello

Support the pipeline operator |

$ echo Hello | tr l L | tr o ?

HeLL?

Evaluation

Total points possible: 7

Minimum number of points required to pass: 5

Points can be obtained as follows:

1 Point: Correct display of shell prompt

1 Point: Read and execute multiple commands

1 Point: Support shell variables and expansion

1 Point: Support $? for displaying the return code of the last program

1 Point: Support & for running programs in the background

1 Point: Support redirection of stdin, stdout and stderr

1 Point: Support pipes with |

the project / source has to compile with the attached makefile

Aptitudini: Programare C, Programare C++, Linux, Arhitectură software, UNIX

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ID Proiect: #28984363