74 lines
2.0 KiB
Plaintext
74 lines
2.0 KiB
Plaintext
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Answer the following questions to describe your code submission. Please keep
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all lines to a maximum of 80 characters wide.
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1 - In pseudo-code, show your general algorithm for setting up two processes
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that are connected by a pipe. You need to show all calls to relevant
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functions (e.g., pipe(), fork(), etc.) but you do not need to show error
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checking or precise syntax.
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pipes[# of processes][2]
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for process in processes:
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pipe(pipes[process #])
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for process in processes:
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if not first process:
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add_dup2(pipes[process #][0], stdin)
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if not last process:
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add_dup2(pipes[process #][1], stdout)
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for pipe in pipes:
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add_close(pipe[0])
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add_close(pipe[1])
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if process is util:
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posix_spawn(process)
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else:
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posix_spawnp(process)
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2 - The project does not ask you to implement pipes with built-ins, but show
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a pseudo-code approach to modifying echo for this purpose. For simplicity,
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ignore the issues of escape characters and environment variables, and
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assume that echo only writes into the pipe. Specifically, what would be
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the flow of relevant functions (pipe(), fork(), etc.) for the following
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command line:
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$ echo hello world | cut -f2
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(HINT: Be careful that you do NOT close or redirect the shell's STDOUT,
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which would prevent it from displaying any more prompts!)
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pipefd[2]
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pipe(fd)
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echo(pipefd[1], "Message") // Modify echo to take in a file descriptor to write to
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close(pipefd[1])
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add_dup2(pipefd[0], stdin)
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add_close(pipefd[0]);
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posix_spawnp("cut", argv)
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close(pipefd[0])
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3 - The project does not ask you to implement file redirection, but show a
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general algorithm in pseudo-code (like above) for the following command
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line (note that 2>&1 says to send STDERR to the same file as STDOUT):
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$ ls > data.txt 2>&1
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fd = open("data.txt")
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add_dup2(fd, stdout)
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add_dup2(fd, stderr)
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add_close(fd)
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posix_spawnp("ls", argv)
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close(fd)
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