The goal of this task is to write a simple but functional UNIX shell in C. It must:
computer science
Description
## 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 > test.txt
$ cat - < test.txt
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 `|`
Instruction Files
README.md
2.3 KB
