project1.htm

· Develop clear, readable, well-documented and well-designed programs in the C Programming Language.

line is called a <I style="mso-bidi-font-style: normal">job</I>. </SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>When executing 
backgrounds jobs, the shell should not wait for the job to finish before 
prompting, reading, and processing the next command. When a background job 
finally terminates a message to that effect must be printed, by the shell, to 
the terminal. This message should be printed as soon as the job 
terminates.</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>The syntax for 
doing this will be described in the section of this document describing the 
shell’s parser.</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Your parser should 
also support several <I style="mso-bidi-font-style: normal">internal 
commands</I> these commands, if issued by the user, should direct the shell to 
take a particular action itself instead of directing it to execute other 
programs. The details of this are discussed in the section describing internal 
commands. </SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<H4><SPAN lang=EN-US>Foreground vs. Background Jobs</SPAN></H4>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Your shell should 
be capable of executing both foreground and background jobs. Whereas your shell 
should wait for foreground jobs to complete before continuing, it should 
immediately continue, prompt the user, &amp;c, after placing a job into the 
background.</SPAN></P>
<H4><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></H4>
<H4><SPAN lang=EN-US>Command lines</SPAN></H4>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><B 
style="mso-bidi-font-weight: normal"><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></B></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>When the user 
responds to a prompt, what they type composes a <I 
style="mso-bidi-font-style: normal">command line string</I>. </SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Your shell should 
store each command-line string, until the job is finished executing. This 
includes both background and suspended jobs.</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>The shell should 
assign each command-line string a non-negative integer identifier. The data 
structure used to store the jobs should allow access to each element using this 
identifier. Once the actions directed by a command-line string are completed, 
your shell should remove it from the data structure. Identifiers can be recycled 
if you choose. Please note that this data structure should keep track of whole 
command line strings, not just the names of the individual tasks that may 
compose them.</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>You should not 
keep track of command line strings that contain internal commands, since, by 
their nature, they will complete before this information could become 
useful.</SPAN></P>
<P class=NormalWeb><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=NormalWeb style="TEXT-INDENT: 36pt"><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>Internal 
Commands<o:p></o:p></SPAN></B></P>
<P class=NormalWeb><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=NormalWeb style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>The following are 
the internal commands. If an internal command is submitted by the user, the 
shell should take the described actions itself.<SPAN 
style="mso-spacerun: yes">&nbsp; </SPAN></SPAN></P>
<P class=NormalWeb><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体">exit</SPAN></B></SPAN><SPAN 
lang=EN-US>: Kill all child processes and exit ysh with a meaningful return 
code.<SPAN style="mso-spacerun: yes">&nbsp; </SPAN></SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体">jobs</SPAN></B></SPAN><SPAN 
lang=EN-US>: Print out the command line strings for jobs that are currently 
executing in the background and jobs that are currently suspended, as well as 
the identifier associated with each command line string. You may format the 
output of this command in way that is convenient to the user. Please remember 
that jobs itself is an internal command and consequently should not appear in 
the output. </SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体">echo 
$status</SPAN></B></SPAN><SPAN lang=EN-US>: Prints the exit status of the most 
recent foreground child process to have exited. Return 0 if no such child has 
existed. </SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体">fg 
%&lt;int&gt;</SPAN></B></SPAN><SPAN lang=EN-US>: Brings the job identified by 
&lt;int&gt; into the foreground. If this job was previously stopped, it should 
now be running. Your shell should wait for a foregound child to terminate before 
returning a command prompt or taking any other action.</SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体">bg 
%&lt;int&gt;</SPAN></B></SPAN><SPAN lang=EN-US>: Execute the suspended job 
identified by &lt;int&gt; in the background.</SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN class=HTMLTypewriter><SPAN lang=EN-US 
style="mso-ansi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">Internal 
commands can take advantage of piped I/O, execute in the background, &amp;c, as 
appropriate</SPAN></SPAN><SPAN lang=EN-US>. </SPAN></P>
<P class=MsoNormal><SPAN class=HTMLTypewriter><B 
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-family: 黑体"><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></B></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>&nbsp;</SPAN></P>
<H5><SPAN lang=EN-US>Special Keystrokes</SPAN></H5>
<P class=MsoNormal><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoBodyTextIndent><SPAN lang=EN-US>Through an interaction with the 
terminal driver, certain combinations of keystrokes will generate signals to 
your shell instead of appearing within stdin. Your shell should respond 
appropriately to these signals. </SPAN></P>
<P class=MsoNormal><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN lang=EN-US>Control-Z generates a SIGSTOP. This 
should not cause your shell to be suspended. Instead, it should cause your shell 
to suspend the processes in the current foreground job. If there is no 
foreground job, it should have no effect.</SPAN></P>
<P class=MsoNormal 
style="MARGIN-LEFT: 54pt; TEXT-INDENT: -18pt; mso-list: l3 level1 lfo5; tab-stops: list 54.0pt"><![if !supportLists]><SPAN 
lang=EN-US 
style="FONT-FAMILY: Symbol; mso-fareast-font-family: 'Times New Roman'">·<SPAN 
style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
</SPAN></SPAN><![endif]><SPAN lang=EN-US>Control-C generates a SIGINT. This 
should not kill your shell. Instead it should cause your shell to kill the 
processes in the current foreground job. If there is no foreground job, it 
should have no effect. </SPAN></P>
<P class=MsoNormal><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<H5><SPAN lang=EN-US>Parsing User Input – Overview, Delimiters and Special 
Characters</SPAN></H5>
<P class=MsoNormal><SPAN 
lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Your parser for 
user input should be capable of accepting input from the user as described in 
this section. It should also detect improper input from the user. If the user 
enters something improper, your shell should produce a meaningful error 
message.</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Just like 
commercial-grade shells, your shell should accept input from the user one line 
at a time. You should begin parsing the users input when he/she hits enter. 
Empty command lines should be treated as no-ops and yield a new prompt. 
</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Blank-space 
characters should be treated as delimiters, but your shell should be insensitive 
to repeated blank spaces. It should also be insensitive to blank spaces at the 
beginning or end of the command line. </SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 36pt"><SPAN lang=EN-US>Certain 
characters, known as <I style="mso-bidi-font-style: normal">meta-characters</I>,