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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>Writing Scripts</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="UP"TITLE="Exercises"HREF="exercises.html"><LINKREL="PREVIOUS"TITLE="Exercises"HREF="exercises.html"><LINKREL="NEXT"TITLE="Revision History"HREF="revisionhistory.html"><METAHTTP-EQUIV="Content-Style-Type"CONTENT="text/css"><LINKREL="stylesheet"HREF="common/kde-common.css"TYPE="text/css"><METAHTTP-EQUIV="Content-Type"CONTENT="text/html; charset=iso-8859-1"><METAHTTP-EQUIV="Content-Language"CONTENT="en"><LINKREL="stylesheet"HREF="common/kde-localised.css"TYPE="text/css"TITLE="KDE-English"><LINKREL="stylesheet"HREF="common/kde-default.css"TYPE="text/css"TITLE="KDE-Default"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#AA0000"VLINK="#AA0055"ALINK="#AA0000"STYLE="font-family: sans-serif;"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="exercises.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Appendix M. Exercises</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="revisionhistory.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="WRITINGSCRIPTS"></A>M.2. Writing Scripts</H1><P><ANAME="WRITINGSCRIPTS1"></A></P><P>Write a script to carry out each of the following tasks.</P><DIVCLASS="VARIABLELIST"><P><B><ANAME="EXEASY1"></A>EASY</B></P><DL><DT><BCLASS="COMMAND">Home Directory Listing</B></DT><DD><P>Perform a recursive directory listing on the user's home directory and save the information to a file. Compress the file, have the script prompt the user to insert a floppy, then press <BCLASS="KEYCAP">ENTER</B>. Finally, save the file to the floppy.</P></DD><DT><BCLASS="COMMAND">Self-reproducing Script</B></DT><DD><P>Write a script that backs itself up, that is, copies itself to a file named <TTCLASS="FILENAME">backup.sh</TT>.</P><P>Hint: Use the <AHREF="external.html#CATREF">cat</A> command and the <AHREF="othertypesv.html#SCRNAMEPARAM">appropriate positional parameter</A>.</P></DD><DT><BCLASS="COMMAND">Converting <AHREF="loops.html#FORLOOPREF1">for</A> loops to <AHREF="loops.html#WHILELOOPREF">while</A> and <AHREF="loops.html#UNTILLOOPREF">until</A> loops</B></DT><DD><P>Convert the <ICLASS="FIRSTTERM">for loops</I> in <AHREF="loops.html#EX22">Example 10-1</A> to <ICLASS="FIRSTTERM">while loops</I>. Hint: store the data in an <AHREF="arrays.html#ARRAYREF">array</A> and step through the array elements.</P><P>Having already done the <SPANCLASS="QUOTE">"heavy lifting"</SPAN>, now convert the loops in the example to <ICLASS="FIRSTTERM"> until loops</I>.</P></DD><DT><BCLASS="COMMAND">Changing the line spacing of a text file</B></DT><DD><P>Write a script that reads each line of a target file, then writes the line back to <TTCLASS="FILENAME">stdout</TT>, but with an extra blank line following. This has the effect of <SPANCLASS="emphasis"><ICLASS="EMPHASIS">double-spacing</I></SPAN> the file.</P><P>Include all necessary code to check whether the script gets the necessary command line argument (a filename), and whether the specified file exists.</P><P>When the script runs correctly, modify it to <SPANCLASS="emphasis"><ICLASS="EMPHASIS">triple-space</I></SPAN> the target file.</P><P>Finally, write a script to remove all blank lines from the target file, <SPANCLASS="emphasis"><ICLASS="EMPHASIS">single-spacing</I></SPAN> it.</P></DD><DT><BCLASS="COMMAND">Backwards Listing</B></DT><DD><P>Write a script that echoes itself to <TTCLASS="FILENAME">stdout</TT>, but <SPANCLASS="emphasis"><ICLASS="EMPHASIS">backwards</I></SPAN>.</P></DD><DT><BCLASS="COMMAND">Automatically Decompressing Files</B></DT><DD><P>Given a list of filenames as input, this script queries each target file (parsing the output of the <AHREF="filearchiv.html#FILEREF">file</A> command) for the type of compression used on it. Then the script automatically invokes the appropriate decompression command (<BCLASS="COMMAND">gunzip</B>, <BCLASS="COMMAND">bunzip2</B>, <BCLASS="COMMAND">unzip</B>, <BCLASS="COMMAND">uncompress</B>, or whatever). If a target file is not compressed, the script emits a warning message, but takes no other action on that particular file.</P></DD><DT><BCLASS="COMMAND">Unique System ID</B></DT><DD><P>Generate a <SPANCLASS="QUOTE">"unique"</SPAN> 6-digit hexadecimal identifier for your computer. Do <SPANCLASS="emphasis"><ICLASS="EMPHASIS">not</I></SPAN> use the flawed <AHREF="system.html#HOSTIDREF">hostid</A> command. Hint: <BCLASS="COMMAND"><AHREF="filearchiv.html#MD5SUMREF">md5sum</A> <TTCLASS="FILENAME">/etc/passwd</TT></B>, then select the first 6 digits of output.</P></DD><DT><BCLASS="COMMAND">Backup</B></DT><DD><P>Archive as a <SPANCLASS="QUOTE">"tarball"</SPAN> (<TTCLASS="FILENAME">*.tar.gz</TT> file) all the files in your home directory tree (<TTCLASS="FILENAME">/home/your-name</TT>) that have been modified in the last 24 hours. Hint: use <AHREF="moreadv.html#FINDREF">find</A>.</P></DD><DT><BCLASS="COMMAND">Checking whether a process is still running</B></DT><DD><P>Given a <AHREF="special-chars.html#PROCESSIDREF">process ID</A> (<ICLASS="FIRSTTERM">PID</I>) as an argument, this script will check, at user-specified intervals, whether the given process is still running. You may use the <AHREF="system.html#PPSSREF">ps</A> and <AHREF="timedate.html#SLEEPREF">sleep</A> commands.</P></DD><DT><BCLASS="COMMAND">Primes</B></DT><DD><P>Print (to stdout) all prime numbers between 60000 and 63000. The output should be nicely formatted in columns (hint: use <AHREF="internal.html#PRINTFREF">printf</A>).</P></DD><DT><BCLASS="COMMAND">Lottery Numbers</B></DT><DD><P>One type of lottery involves picking five different numbers, in the range of 1 - 50. Write a script that generates five pseudorandom numbers in this range, <SPANCLASS="emphasis"><ICLASS="EMPHASIS">with no duplicates</I></SPAN>. The script will give the option of echoing the numbers to <TTCLASS="FILENAME">stdout</TT> or saving them to a file, along with the date and time the particular number set was generated.</P></DD></DL></DIV><DIVCLASS="VARIABLELIST"><P><B><ANAME="EXMEDIUM1"></A>INTERMEDIATE</B></P><DL><DT><BCLASS="COMMAND">Integer or String</B></DT><DD><P>Write a script <AHREF="functions.html#FUNCTIONREF">function</A> that determines if an argument passed to it is an integer or a string. The function will return TRUE (0) if passed an integer, and FALSE (1) if passed a string.</P><P>Hint: What does the following expression return when <TTCLASS="VARNAME">$1</TT> is <SPANCLASS="emphasis"><ICLASS="EMPHASIS">not</I></SPAN> an integer?</P><P><TTCLASS="VARNAME">expr $1 + 0</TT></P></DD><DT><BCLASS="COMMAND">Managing Disk Space</B></DT><DD><P>List, one at a time, all files larger than 100K in the <TTCLASS="FILENAME">/home/username</TT> directory tree. Give the user the option to delete or compress the file, then proceed to show the next one. Write to a logfile the names of all deleted files and the deletion times.</P></DD><DT><BCLASS="COMMAND">Removing Inactive Accounts</B></DT><DD><P>Inactive accounts on a network waste disk space and may become a security risk. Write an administrative script (to be invoked by <ICLASS="FIRSTTERM">root</I> or the <AHREF="system.html#CRONREF">cron daemon</A>) that checks for and deletes user accounts that have not been accessed within the last 90 days.</P></DD><DT><BCLASS="COMMAND">Enforcing Disk Quotas</B></DT><DD><P>Write a script for a multi-user system that checks users' disk usage. If a user surpasses the preset limit (100 MB, for example) in her <TTCLASS="FILENAME">/home/username</TT> directory, then the script will automatically send her a warning e-mail.</P><P>The script will use the <AHREF="system.html#DUREF">du</A> and <AHREF="communications.html#COMMMAIL1">mail</A> commands. As an option, it will allow setting and enforcing quotas using the <AHREF="system.html#QUOTAREF">quota</A> and <AHREF="system.html#SETQUOTAREF">setquota</A> commands.</P></DD><DT><BCLASS="COMMAND">Logged in User Information</B></DT><DD><P>For all logged in users, show their real names and the time and date of their last login.</P><P>Hint: use <AHREF="system.html#WHOREF">who</A>, <AHREF="system.html#LASTLOGREF">lastlog</A>, and parse <TTCLASS="FILENAME">/etc/passwd</TT>.</P></DD><DT><BCLASS="COMMAND">Safe Delete</B></DT><DD><P>Implement, as a script, a <SPANCLASS="QUOTE">"safe"</SPAN> delete command, <TTCLASS="FILENAME">sdel.sh</TT>. Filenames passed as command-line arguments to this script are not deleted, but instead <AHREF="filearchiv.html#GZIPREF">gzipped</A> if not already compressed (use <AHREF="filearchiv.html#FILEREF">file</A> to check), then moved to a <TTCLASS="FILENAME">~/TRASH</TT> directory. Upon invocation, the script checks the <TTCLASS="FILENAME">~/TRASH</TT> directory for files older than 48 hours and <AHREF="external.html#RMREF">permanently deletes</A> them. (An better alternative might be to have a second script handle this -- periodically invoked by the <AHREF="system.html#CRONREF">cron daemon</A>.)</P><P><SPANCLASS="emphasis"><ICLASS="EMPHASIS">Extra credit:</I></SPAN> Write the script so it can handle files and directories <AHREF="external.html#RMRECURS">recursively</A>. This would give it the capability of <SPANCLASS="QUOTE">"safely deleting"</SPAN> entire directory structures.</P></DD><DT><BCLASS="COMMAND">Making Change</B⌨️ 快捷键说明
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