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<a class="dropdown-item" href="IntroConcSysOverview.html"> 1.1. Introduction to Concurrent Systems</a>
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<a class="dropdown-item" href="SysAndModels.html"> 1.2. Systems and Models</a>
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<a class="dropdown-item" href="SequenceModels.html"> 1.6. Sequence Models in UML</a>
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<a class="dropdown-item" href="StateModelImplementation.html"> 1.7. Extended Example: State Model Implementation</a>
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<a class="dropdown-item disabled"><b>Chapter 2</b></a>
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<a class="dropdown-item" href="ProcessesOverview.html"> 2.1. Processes and OS Basics</a>
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<a class="dropdown-item" href="Multiprogramming.html"> 2.2. Processes and Multiprogramming</a>
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<a class="dropdown-item" href="Syscall.html"> 2.4. System Call Interface</a>
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<a class="dropdown-item" href="UnixFile.html"> 2.6. The UNIX File Abstraction</a>
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<a class="dropdown-item" href="EventsSignals.html"> 2.7. Events and Signals</a>
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<a class="dropdown-item" href="Extended2Processes.html"> 2.8. Extended Example: Listing Files with Processes</a>
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<a class="dropdown-item" href="IPCOverview.html"> 3.1. Concurrency with IPC</a>
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<a class="dropdown-item" href="IPCModels.html"> 3.2. IPC Models</a>
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<a class="dropdown-item" href="Pipes.html"> 3.3. Pipes and FIFOs</a>
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<a class="dropdown-item" href="MMap.html"> 3.4. Shared Memory With Memory-mapped Files</a>
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<a class="dropdown-item" href="POSIXvSysV.html"> 3.5. POSIX vs. System V IPC</a>
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<a class="dropdown-item" href="ShMem.html"> 3.7. Shared Memory</a>
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<a class="dropdown-item" href="IPCSems.html"> 3.8. Semaphores</a>
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<a class="dropdown-item" href="Extended3Bash.html"> 3.9. Extended Example: Bash-lite: A Simple Command-line Shell</a>
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<a class="dropdown-item disabled"><b>Chapter 4</b></a>
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<a class="dropdown-item" href="SocketsOverview.html"> 4.1. Networked Concurrency</a>
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<a class="dropdown-item" href="FiveLayer.html"> 4.2. The TCP/IP Internet Model</a>
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<a class="dropdown-item" href="NetApps.html"> 4.3. Network Applications and Protocols</a>
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<a class="dropdown-item" href="Sockets.html"> 4.4. The Socket Interface</a>
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<a class="dropdown-item" href="TCPSockets.html"> 4.5. TCP Socket Programming: HTTP</a>
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<a class="dropdown-item" href="UDPSockets.html"> 4.6. UDP Socket Programming: DNS</a>
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<a class="dropdown-item disabled"><b>Chapter 5</b></a>
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<a class="dropdown-item" href="InternetOverview.html"> 5.1. The Internet and Connectivity</a>
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<a class="dropdown-item" href="ThreadsOverview.html"> 6.1. Concurrency with Multithreading</a>
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<a class="dropdown-item" href="RaceConditions.html"> 6.3. Race Conditions and Critical Sections</a>
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<a class="dropdown-item" href="POSIXThreads.html"> 6.4. POSIX Thread Library</a>
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<a class="dropdown-item" href="ThreadArgs.html"> 6.5. Thread Arguments and Return Values</a>
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<a class="dropdown-item" href="ImplicitThreads.html"> 6.6. Implicit Threading and Language-based Threads</a>
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<a class="dropdown-item" href="Extended6Input.html"> 6.7. Extended Example: Keyboard Input Listener</a>
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<a class="dropdown-item" href="Extended6Primes.html"> 6.8. Extended Example: Concurrent Prime Number Search</a>
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<a class="dropdown-item" href="SynchOverview.html"> 7.1. Synchronization Primitives</a>
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<a class="dropdown-item" href="CritSect.html"> 7.2. Critical Sections and Peterson's Solution</a>
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<a class="dropdown-item" href="Locks.html"> 7.3. Locks</a>
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<a class="dropdown-item" href="SynchProblemsOverview.html"> 8.1. Synchronization Patterns and Problems</a>
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<a class="dropdown-item" href="SynchDesign.html"> 8.2. Basic Synchronization Design Patterns</a>
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<a class="dropdown-item" href="ProdCons.html"> 8.3. Producer-Consumer Problem</a>
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<a class="dropdown-item" href="ReadWrite.html"> 8.4. Readers-Writers Problem</a>
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<a class="dropdown-item" href="DiningPhil.html"> 8.5. Dining Philosophers Problem and Deadlock</a>
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<a class="dropdown-item" href="CigSmokers.html"> 8.6. Cigarette Smokers Problem and the Limits of Semaphores and Locks</a>
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<a class="dropdown-item" href="Extended8ModExp.html"> 8.7. Extended Example: Parallel Modular Exponentiation</a>
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<a class="dropdown-item disabled"><b>Chapter 9</b></a>
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<a class="dropdown-item" href="ParallelDistributedOverview.html"> 9.1. Parallel and Distributed Systems</a>
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<a class="dropdown-item" href="ParVConc.html"> 9.2. Parallelism vs. Concurrency</a>
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<a class="dropdown-item" href="Scaling.html"> 9.4. Limits of Parallelism and Scaling</a>
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<a class="dropdown-item" href="DistDataStorage.html"> 9.6. Reliable Data Storage and Location</a>
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<a class="dropdown-item" href="DistConsensus.html"> 9.7. Consensus in Distributed Systems</a>
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<a class="dropdown-item" href="Extended9Blockchain.html"> 9.8. Extended Example: Blockchain Proof-of-Work</a>
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<a class="dropdown-item" href="CLangOverview.html"> A.1. C Language Reintroduction</a>
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<script>ODSA.SETTINGS.DISP_MOD_COMP = true;ODSA.SETTINGS.MODULE_NAME = "Extended3Bash";ODSA.SETTINGS.MODULE_LONG_NAME = "Extended Example: Bash-lite: A Simple Command-line Shell";ODSA.SETTINGS.MODULE_CHAPTER = "Concurrency with IPC"; ODSA.SETTINGS.BUILD_DATE = "2021-06-01 15:31:50"; ODSA.SETTINGS.BUILD_CMAP = false;JSAV_OPTIONS['lang']='en';JSAV_EXERCISE_OPTIONS['code']='java';</script><div class="section" id="extended-example-bash-lite-a-simple-command-line-shell">
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<h1>3.9. Extended Example: Bash-lite: A Simple Command-line Shell<a class="headerlink" href="Extended3Bash.html#extended-example-bash-lite-a-simple-command-line-shell" title="Permalink to this headline">¶</a></h1>
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<p>This Extended Example creates a minimal shell similar to the bash shell used in Linux and macOS.
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When this program runs, it will read a line of text at a time from the user. This line will be used
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as a command line, running in a separate process. The user can enter <code class="docutils literal notranslate"><span class="pre">quit</span></code> or <code class="docutils literal notranslate"><span class="pre">logout</span></code> to exit.</p>
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<div class="highlight-c border border-dark rounded-lg bg-light px-0 mb-3 notranslate"><table class="highlighttable"><tr><td class="linenos px-0 mx-0"><div class="linenodiv"><pre class="mb-0"> 1
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194</pre></div></td><td class="code"><div class="highlight bg-light"><pre class="mb-0"><span></span><span class="cp">#include</span> <span class="cpf"><assert.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><fcntl.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><stdbool.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><stdio.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><stdlib.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><string.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><sys/stat.h></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><unistd.h></span><span class="cp"></span>
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<span class="cm">/* Set the maximum allowable length for a command line */</span>
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<span class="cp">#define MAX_LINE_LENGTH 1024</span>
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<span class="cm">/* Allow spaces, tabs, newline, and carriage return to match</span>
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<span class="cm"> whitespace between tokens */</span>
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<span class="cp">#define WHITESPACE " \t\n\r"</span>
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<span class="kt">void</span> <span class="nf">run_child_process</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="p">);</span>
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<span class="kt">char</span> <span class="o">**</span><span class="nf">tokenize_arguments</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="p">);</span>
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<span class="kt">char</span> <span class="o">**</span><span class="nf">get_out_name</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="p">);</span>
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<span class="kt">int</span>
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<span class="nf">main</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="kt">char</span> <span class="n">buffer</span><span class="p">[</span><span class="n">MAX_LINE_LENGTH</span> <span class="o">+</span> <span class="mi">1</span><span class="p">];</span>
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<span class="n">memset</span> <span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">MAX_LINE_LENGTH</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
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<span class="cm">/* Main loop: iterate until user enters "quit" or "logout" */</span>
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<span class="k">while</span> <span class="p">(</span><span class="nb">true</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="cm">/* Display a minimal prompt and read the command line */</span>
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<span class="n">printf</span> <span class="p">(</span><span class="s">"$ "</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span> <span class="n">fgets</span> <span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="n">MAX_LINE_LENGTH</span><span class="p">,</span> <span class="n">stdin</span><span class="p">))</span>
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<span class="k">break</span><span class="p">;</span>
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<span class="cm">/* Get the command for this line without any arguments */</span>
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<span class="kt">char</span> <span class="o">*</span><span class="n">command</span> <span class="o">=</span> <span class="n">strtok</span> <span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="n">WHITESPACE</span><span class="p">);</span>
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<span class="cm">/* Check for reserved keywords to quit the shell */</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span> <span class="n">strncmp</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="s">"quit"</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span> <span class="o">||</span> <span class="o">!</span> <span class="n">strncmp</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="s">"logout"</span><span class="p">,</span> <span class="mi">7</span><span class="p">))</span>
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<span class="k">break</span><span class="p">;</span>
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<span class="cm">/* Get the array of arguments and determine the output file</span>
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<span class="cm"> to use (if the line ends with "> output" redirection). */</span>
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<span class="kt">char</span> <span class="o">*</span><span class="n">output</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
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<span class="kt">char</span> <span class="o">**</span><span class="n">arg_list</span> <span class="o">=</span> <span class="n">tokenize_arguments</span> <span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="o">&</span><span class="n">output</span><span class="p">);</span>
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<span class="cm">/* Security precaution: This is a simple shell that should</span>
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<span class="cm"> not be used for running commands in root. */</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span> <span class="n">strncmp</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="s">"sudo"</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span> <span class="o">||</span> <span class="o">!</span> <span class="n">strncmp</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="s">"su"</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span>
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<span class="p">{</span>
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<span class="n">printf</span> <span class="p">(</span><span class="s">"*WARNING* This implementation does not "</span>
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<span class="s">"support super-user commands</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
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<span class="k">continue</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="cm">/* If something went wrong, skip this line */</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">arg_list</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="n">perror</span> <span class="p">(</span><span class="s">"-bash-lite: syntax error</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
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<span class="k">continue</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="cm">/* Copy the command name as the first argument */</span>
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<span class="n">arg_list</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="n">command</span><span class="p">;</span>
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<span class="cm">/* Create the child process and execute the command in it */</span>
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<span class="kt">pid_t</span> <span class="n">child_pid</span> <span class="o">=</span> <span class="n">fork</span> <span class="p">();</span>
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<span class="n">assert</span> <span class="p">(</span><span class="n">child_pid</span> <span class="o">>=</span> <span class="mi">0</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">child_pid</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
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<span class="n">run_child_process</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="n">arg_list</span><span class="p">,</span> <span class="n">output</span><span class="p">);</span>
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<span class="cm">/* Parent waits for the child, then frees up allocated memory</span>
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<span class="cm"> for the argument list and moves on to the next line */</span>
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<span class="n">wait</span> <span class="p">(</span><span class="nb">NULL</span><span class="p">);</span>
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<span class="n">free</span> <span class="p">(</span><span class="n">arg_list</span><span class="p">);</span>
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<span class="n">memset</span> <span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">MAX_LINE_LENGTH</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="n">EXIT_SUCCESS</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="cm">/* Runs a command in an already created child process. The command</span>
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<span class="cm"> string should already be copied as the first argument in the</span>
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<span class="cm"> list. If the user typed an output redirection ("> out" or</span>
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<span class="cm"> ">out"), then output_file is the name of the file to create.</span>
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<span class="cm"> Otherwise, output_file is NULL. Should never return. */</span>
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<span class="kt">void</span>
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<span class="nf">run_child_process</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">command</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">arg_list</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="n">output_file</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="kt">int</span> <span class="n">out_fd</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
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<span class="cm">/* If there is a specified output file, open it and redirect</span>
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<span class="cm"> STDOUT to write to this file */</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">output_file</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="n">out_fd</span> <span class="o">=</span> <span class="n">open</span> <span class="p">(</span><span class="n">output_file</span><span class="p">,</span> <span class="n">O_RDWR</span> <span class="o">|</span> <span class="n">O_CREAT</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">out_fd</span> <span class="o"><</span> <span class="mi">0</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="n">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"-bash-lite: failed to open file %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">output_file</span><span class="p">);</span>
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<span class="n">exit</span> <span class="p">(</span><span class="n">EXIT_FAILURE</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="cm">/* Make the file readable and redirect STDOUT */</span>
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<span class="n">fchmod</span> <span class="p">(</span><span class="n">out_fd</span><span class="p">,</span> <span class="mo">0644</span><span class="p">);</span>
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<span class="n">dup2</span> <span class="p">(</span><span class="n">out_fd</span><span class="p">,</span> <span class="n">STDOUT_FILENO</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="cm">/* Use execvp, because we are not doing a PATH lookup and the</span>
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<span class="cm"> arguments are in a dynamically allocated array */</span>
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<span class="n">execvp</span> <span class="p">(</span><span class="n">command</span><span class="p">,</span> <span class="n">arg_list</span><span class="p">);</span>
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<span class="cm">/* Should never reach here. Print an error message, free up</span>
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<span class="cm"> resources, and exit. */</span>
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<span class="n">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"-bash-lite: %s: command not found</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">command</span><span class="p">);</span>
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<span class="n">free</span> <span class="p">(</span><span class="n">arg_list</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">out_fd</span> <span class="o">>=</span> <span class="mi">0</span><span class="p">)</span>
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<span class="n">close</span> <span class="p">(</span><span class="n">out_fd</span><span class="p">);</span>
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<span class="n">exit</span> <span class="p">(</span><span class="n">EXIT_FAILURE</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="cm">/* Given a command line (buffer), create the list of arguments to</span>
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<span class="cm"> use for the child process. If the command line ends in an output</span>
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<span class="cm"> redirection, update the output_file pointer to point to the name</span>
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<span class="cm"> of the file to use. */</span>
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<span class="kt">char</span> <span class="o">**</span>
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<span class="nf">tokenize_arguments</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">buffer</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">output_file</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="n">assert</span> <span class="p">(</span><span class="n">buffer</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
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<span class="n">assert</span> <span class="p">(</span><span class="n">output_file</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
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<span class="kt">char</span> <span class="o">*</span><span class="n">token</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
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<span class="cm">/* Allocate an initial array for 10 arguments; this can grow</span>
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<span class="cm"> later if needed */</span>
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<span class="kt">size_t</span> <span class="n">arg_list_capacity</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
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<span class="kt">char</span> <span class="o">**</span><span class="n">arguments</span> <span class="o">=</span> <span class="n">calloc</span> <span class="p">(</span><span class="n">arg_list_capacity</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">));</span>
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<span class="n">assert</span> <span class="p">(</span><span class="n">arguments</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
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<span class="cm">/* Leave the first space blank for the command name */</span>
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<span class="kt">size_t</span> <span class="n">arg_list_length</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
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<span class="k">while</span> <span class="p">(</span> <span class="p">(</span><span class="n">token</span> <span class="o">=</span> <span class="n">strtok</span> <span class="p">(</span><span class="nb">NULL</span><span class="p">,</span> <span class="n">WHITESPACE</span><span class="p">))</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="cm">/* If token starts with >, it is an output redirection. The</span>
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<span class="cm"> rest of the line must be the file name. Need to pass both</span>
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<span class="cm"> the rest of the token and the buffer, as there might not</span>
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<span class="cm"> be a space before the file name. */</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">token</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">==</span> <span class="sc">'>'</span><span class="p">)</span>
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<span class="k">return</span> <span class="n">get_out_name</span> <span class="p">(</span><span class="o">&</span><span class="n">token</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="n">output_file</span><span class="p">,</span> <span class="n">arguments</span><span class="p">);</span>
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<span class="cm">/* If current argument array is full, double its capacity */</span>
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<span class="k">if</span> <span class="p">((</span><span class="n">arg_list_length</span> <span class="o">+</span> <span class="mi">1</span><span class="p">)</span> <span class="o">==</span> <span class="n">arg_list_capacity</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="n">arg_list_capacity</span> <span class="o">*=</span> <span class="mi">2</span><span class="p">;</span>
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<span class="n">arguments</span> <span class="o">=</span> <span class="n">realloc</span> <span class="p">(</span><span class="n">arguments</span><span class="p">,</span> <span class="n">arg_list_capacity</span> <span class="o">*</span> <span class="k">sizeof</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">));</span>
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<span class="n">assert</span> <span class="p">(</span><span class="n">arguments</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="cm">/* Add the token to the end of the argument list */</span>
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<span class="n">arguments</span><span class="p">[</span><span class="n">arg_list_length</span><span class="o">++</span><span class="p">]</span> <span class="o">=</span> <span class="n">token</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="n">arguments</span><span class="p">;</span>
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|
<span class="p">}</span>
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<span class="cm">/* Determine the output file from either the token that begins with</span>
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<span class="cm"> the '>' character (but that character was removed) or from the</span>
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<span class="cm"> next token on the command line. Note that all tokens after the</span>
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<span class="cm"> output file name will be ignored. */</span>
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<span class="kt">char</span> <span class="o">**</span>
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<span class="nf">get_out_name</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">token</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">output_file</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">arguments</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="cm">/* If token is not an empty string, it contains the output file</span>
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<span class="cm"> name */</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">strlen</span> <span class="p">(</span><span class="n">token</span><span class="p">)</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)</span>
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|
<span class="p">{</span>
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<span class="o">*</span><span class="n">output_file</span> <span class="o">=</span> <span class="n">token</span><span class="p">;</span>
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|
<span class="k">return</span> <span class="n">arguments</span><span class="p">;</span>
|
|
<span class="p">}</span>
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|
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<span class="cm">/* Token is empty, so there was a space after the '>' symbol.</span>
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|
<span class="cm"> There should be one token left that is the file name. */</span>
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|
<span class="n">token</span> <span class="o">=</span> <span class="n">strtok</span> <span class="p">(</span><span class="nb">NULL</span><span class="p">,</span> <span class="n">WHITESPACE</span><span class="p">);</span>
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|
<span class="k">if</span> <span class="p">(</span><span class="n">token</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span>
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|
<span class="p">{</span>
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|
<span class="cm">/* This is an error, no file name was passed */</span>
|
|
<span class="n">free</span> <span class="p">(</span><span class="n">arguments</span><span class="p">);</span>
|
|
<span class="k">return</span> <span class="nb">NULL</span><span class="p">;</span>
|
|
<span class="p">}</span>
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|
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|
<span class="cm">/* The last token is the file name, so return it and the argument </span>
|
|
<span class="cm"> list */</span>
|
|
<span class="o">*</span><span class="n">output_file</span> <span class="o">=</span> <span class="n">token</span><span class="p">;</span>
|
|
<span class="k">return</span> <span class="n">arguments</span><span class="p">;</span>
|
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<span class="p">}</span>
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</pre></div>
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