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in middle of rewrite/simplify

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Remzi Arpaci-Dusseau
2018-02-05 07:35:36 -06:00
parent 84738b9ddf
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processes-shell/README.md
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@@ -22,11 +22,9 @@ creates a child process that executes the command you entered and then prompts
for more user input when it has finished. for more user input when it has finished.
The shells you implement will be similar to, but simpler than, the one you run The shells you implement will be similar to, but simpler than, the one you run
every day in Unix. You can find out which shell you are running by typing every day in Unix. If you don't know what shell you are running, it's probably
**echo $SHELL**] at a prompt. You may then wish to look at the man pages for `bash`. One thing you should do on your own time is learn more about your
the shell you are running (probably bash) to learn more about all of the shell, by reading the man pages or other online materials.
functionality that can be present. For this project, you do not need to
implement too much functionality.
## Program Specifications ## Program Specifications
@@ -45,14 +43,10 @@ prompt> ./wish
You should structure your shell such that it creates a new process for each You should structure your shell such that it creates a new process for each
new command (note that there are a few exceptions to this, which we discuss new command (note that there are a few exceptions to this, which we discuss
below). There are two advantages of creating a new process. First, it protects below). Your basic shell should be able to parse a command and run the
the main shell process from any errors that occur in the new command. Second, program corresponding to the command. For example, if the user types `ls
it allows for concurrency; that is, multiple commands can be started and -la /tmp`, your shell should run the program `/bin/ls` with the given
allowed to execute simultaneously. arguments `-la` and `/tmp`.
Your basic shell should be able to parse a command, and run the program
corresponding to the command. For example, if the user types `ls -la /tmp`,
your shell should run the program `/bin/ls` with all the given arguments.
You might be wondering how the shell knows to run `/bin/ls` (which means the You might be wondering how the shell knows to run `/bin/ls` (which means the
program binary `ls` is found in the directory `/bin`) when you type `ls`. The program binary `ls` is found in the directory `/bin`) when you type `ls`. The
@@ -60,10 +54,15 @@ shells knows this thanks to a **path** variable that the user sets. The path
variable contains the list of all directories to search, in order, when the variable contains the list of all directories to search, in order, when the
user types a command. We'll learn more about how to deal with the path below. user types a command. We'll learn more about how to deal with the path below.
**Important:** Note that the shell itself does not *implement* `code ls` or **Important:** Note that the shell itself does not *implement* `ls` or really
really many other commands at all. All it does is find those executables in many other commands at all (it does implement a few, called *built-ins*,
one of the directories specified by `path` and create a new process to described further below). All it does is find those executables in one of the
run them. More on this below. directories specified by `path` and create a new process to run them. More on
this below.
## Built-in Commands ## Built-in Commands