MALLOC FAILURE:
if a 'malloc failure' occurs minishell doesn't execute the command.
It may open files and ask you to fill here-documents before the malloc failure,
int that it will dispose of all the file descriptor and memory allocated.
The only exceptions are builtins: If a malloc failure occurs during the execution of a builtin
the behaviour is undefined, nevertheless all the open file descriptors and dynamically allocated
memory will be handled and the shell will display a new prompt.

PIPE FAILURE:
If a 'pipe failure' occurs the output will be redirected towards STDOUT_FILENO.
The input of the following command will be read from STDIN_FILENO instead.
If the here-document pipe fails the input will be taken from stdin instead at the time of execution.

FORK FAILURE:
If a 'fork failure' occurs the command isn't executed, the pipeline is truncated and
'$?' is set to the last command executed.