Lab46 Wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
<WRAP round box>
\\ 
<WRAP centeralign bigger><WRAP bigger fgred>Corning Community College</WRAP>
\\ 
<WRAP muchbigger>UNIX/Linux Fundamentals</WRAP> 
\\ 
\\ 
Case Study 0xD: Analyzing Shell Script Logic
\\ 
\\ 
</WRAP>
</WRAP>
~~TOC~~
======Objective======
To gain additional familiarity with shell scripting.
======Background======

Shell scripting enables you countless possibilities for automating tasks, both menial and sophisticated in nature.

However, like any new tool or concept, one needs to spend time with, and play with things, to get a better understanding.

======Exploration======
Analyze, poke at, and get running the following script on Lab46:

<code bash>
#!/bin/bash
    
month="`date +%m`"
year="`date +%Y`"
day="`date +%d`"

today="${year}${month}${day}"
csem=""
for item in `wget -q -O - http://www.corning-cc.edu/future/acacalendar/ \
        | grep 'Semester begins' | sed 's/\.\.*/:/g' \
        | sed 's/<[/a-z0-9]*>//g' | sed 's/:Semester begins : /:/g' \
        | sed 's/:First Summer Session begins : /:/g' \
        | egrep -o '[FWS][a-z]* [0-9]{4} S[a-z]*:[A-Z][a-z]* [1-9][0-9]?' \
        | tr 'WSF' 'wsf' | sed 's/ \([1-9][0-9][0-9][0-9]\) semester/\1/g' \
        | sed 's/ /*/g'`; do
    sm="`echo $item | cut -d':' -f1`"
    out=$(date --date "`echo $item \
        | sed 's/^[a-z]*\([0-9]*\):\([A-Za-z]*\)\*\([0-9]*\)$/\2 \3 \1/'`" \
        +%Y%m%d)
            
    if [ "$today" -ge "$out" ]; then
        csem="$sm"
    fi  
done
echo "$csem"

if [ -z "$csem" ]; then
    status=1
else
    status=0
fi

exit $status
</code>

======Questions======

  - What is the purpose of this script?
  - What is the general flow of operations that takes place in this script?
  - Explain what **today="${year}${month}${day}"** does.
  - What does **<nowiki>sed 's/<[/a-z0-9]*>//g'</nowiki>** appear to do?
  - What are the raw **$item** values being iterated in the for loop?
  - What is the purpose of the **if** statement?
  - Any potential bugs that could effect proper operation?
  - What is the significance of exiting with a value of **0** vs. that of **1**?

======Conclusions======
All questions in this assignment require an action or response. Please organize your responses into an easily readable format and submit the final results to your instructor.

Your assignment is expected to be performed and submitted in a clear and organized fashion- messy or unorganized assignments may have points deducted. Be sure to adhere to the submission policy.

The successful results of the following actions will be considered for evaluation:

  * your responses to questions submitted at the following form:

<html><center><a href="http://lab46.corning-cc.edu/haas/content/unix/submit.php?csd">http://lab46.corning-cc.edu/haas/content/unix/submit.php?csd</a></center></html>
\\ 

  * the response from the form (received via e-mail) saved as **csd.txt** to your **~/src/unix/** directory
  * addition/commit of **~/src/unix/csd.txt** into your repository (CS 0x0 sets you up to do this).

As always, the class mailing list and class IRC channel are available for assistance, but not answers.
Lab46 Wiki

User Tools

Site Tools

Page Tools
