updated

LDP/howto/linuxdoc/Bash-Prog-Intro-HOWTO.sgml

@@ -9,7 +9,7 @@
 <article>
     <title>BASH Programming - Introduction HOW-TO</title>
     <author>by Mike G <tt/mikkey@dynamo.com.ar/</author>
-    <date>v0.06, 21 June 2000</date>
+    <date>v0.07, 22 June 2000</date>
     <abstract> 
     This article intends to help you to start programming 
     basic-intermediate shell scripts. It does not intend to be an 
@@ -26,17 +26,17 @@
 <sect>
 Introduction
 
-<!--
+
      <sect1>
      Getting the latest version
 
-     <P> View it online
-     <htmlurl url=""
-     name="">
+	<p>
+     <htmlurl url="http://www.linuxdoc.org/HOWTO/Bash-Prog-Intro-HOWTO.html"
+     name="http://www.linuxdoc.org/HOWTO/Bash-Prog-Intro-HOWTO.html">
 
 
      </sect1>
--->
+
      <sect1>
      Requisites
           <P> Familiarity with GNU/Linux command lines, and familiarity 
@@ -82,14 +82,14 @@ Very simple Scripts
 	<P>
 	<tscreen><verb>
 	  #!/bin/bash          
-	  echo Hello World!    
+	  echo Hello World    
 	</verb></tscreen>
 	<P> 
 	<P> This script has only two lines. 
         The first indicates the system which program 
         to use to run the file. 
         <P> The second line is the only action performed by this script, 
-        which prints 'Hello World! on the terminal.
+        which prints 'Hello World' on the terminal.
     </sect1>
     <sect1>
     A very simple backup script
@@ -111,7 +111,7 @@ All about redirection
 
 	<sect1>
 	Theory and quick reference
-	<p> There are 3 file descriptors, stdin, stdout and stderr (std=standar)
+	<p> There are 3 file descriptors, stdin, stdout and stderr (std=standard).
 
 	<p>Basically you can:
 	<enum>
@@ -123,7 +123,7 @@ All about redirection
 	<item> redirect stderr and stdout to stdout 
 	<item> redirect stderr and stdout to stderr
 	</enum>
-	1 'represents' stdout and 2 stderr
+	1 'represents' stdout and 2 stderr.
 	<p> A little note for seeing this things: with the less command you can view both stdout 
 	(which will remain on the buffer) and the stderr that will be printed on the screen, but erased as 
 	you try to 'browse' the buffer. 
@@ -131,7 +131,7 @@ All about redirection
 	
 	<sect1>
 	Sample: stdout 2 file 
-	<p> This will cause the ouput of a program to be writen to a file
+	<p> This will cause the ouput of a program to be written to a file.
 	<tscreen><verb>
 	ls -l > ls-l.txt
 	</verb></tscreen>
@@ -141,7 +141,7 @@ All about redirection
 
 	<sect1>
 	Sample: stderr 2 file 
-	<p> This will cause the stderr ouput of a program to be writen to a file
+	<p> This will cause the stderr ouput of a program to be written to a file.
 	<tscreen><verb>
 	grep da * 2> grep-errors.txt
 	</verb></tscreen>
@@ -151,7 +151,7 @@ All about redirection
 
 	<sect1>
 	Sample: stdout 2 stderr
-	<p> This will cause the stderr ouput of a program to be writen to the same filedescriptor 
+	<p> This will cause the stderr ouput of a program to be written to the same filedescriptor 
 	than stdout.
 	<tscreen><verb>
 	grep da * 1>&2 
@@ -161,7 +161,7 @@ All about redirection
 
 	<sect1>
 	Sample: stderr 2 stdout 
-	<p> This will cause the stderr ouput of a program to be writen to the same filedescriptor 
+	<p> This will cause the stderr ouput of a program to be written to the same filedescriptor 
 	than stdout.
 	<tscreen><verb>
 	grep * 2>&1
@@ -266,6 +266,7 @@ Variables
 	<P>  You have no need to declare a variable, just 
         assigning a value to its reference will create it.
 
+	
 
     <!-- Samples -->
         <sect1>
@@ -284,6 +285,7 @@ Variables
 	    that if you don't use the '$' sign, the output of the program will
 	    be different, and probably not what you want it to be.
 	</sect1>
+
         <sect1>
 	   Sample: A very simple backup script (little bit better)
 	   <P> 
@@ -301,13 +303,32 @@ Variables
 	   command inside the parenthesis, capturing its output. 
 
 	   <P> Notice that in this script, the output filename will
-	   be different 
-	   every day, due to the format switch to the date command(+%Y%m%d).
+	   be different every day, due to the format switch to the date command(+%Y%m%d).
 	   You can change this by specifying a different format.
 	   <P> Some more examples:
 	   <P> echo ls
 	   <P> echo $(ls)
-	</sect1>   
+	</sect1>  
+
+	<sect1>
+	Local variables
+
+	<p> Local variables can be created by using the keyword <it/local/.
+
+	<tscreen><verb>
+		#!/bin/bash
+		HELLO=Hello 
+		function hello {
+			local HELLO=World
+			echo $HELLO
+		}
+		echo $HELLO
+		hello
+		echo $HELLO
+	</verb></tscreen>
+	<p> This example should be enought to show how to use a local variable. 
+	</sect1>
+ 
 </sect>
 
 <!-- Conditionals -->
@@ -486,16 +507,16 @@ Functions
      <sect1>
      Functions sample
            <P> <tscreen><verb>
-	   1)  #!/bin/bash 
-	   2)  function quit {
-	   3)      exit
-	   4)  }
-	   5)  function hello {
-	   6)      echo Hello!
-	   7)  }
-	   8)  hello
-	   9)  quit
-	   10) echo foo 
+	   #!/bin/bash 
+	   function quit {
+	       exit
+	   }
+	   function hello {
+	       echo Hello!
+	   }
+	   hello
+	   quit
+	   echo foo 
 	   </verb></tscreen>
 	   <P> Lines 2-4 contain the 'quit' function. Lines 5-7 contain the 'hello' function
 	   If you are not absolutely sure about what this script does, please try it!.
@@ -503,6 +524,29 @@ Functions
 	   <P> When running the script you'll notice that first: the function 'hello' is 
 	   called, second the 'quit' function, and the program never reaches line 10.
      </sect1>
+
+     <sect1>
+     Functions with parameters sample
+           <P> <tscreen><verb>
+		#!/bin/bash 
+		function quit {
+ 		   exit
+		}  
+		function e {
+		    echo $1 
+		}  
+		e Hello
+		e World
+		quit
+		echo foo 
+
+	   </verb></tscreen>
+	   <P> This script is almos identically to the previous one. The main difference is the 
+		funcion 'e'. This function, prints the first argument it receives. 
+		Arguments, within funtions, are treated in the same manner as arguments given to the script.
+     </sect1>
+
+
 </sect>
 
 
@@ -563,8 +607,23 @@ User interfaces
 Misc
     <!-- Reading user input  -->    
     <sect1>
-    Reading user input
-         <P> __TO-DO__
+    Reading user input with read
+         <P> In many ocations you may want to prompt the user for some input, and there are several ways 
+		to achive this. This is one of those ways:
+	<tscreen><verb>
+		#!/bin/bash
+		echo Please, enter your name
+		read NAME
+		echo "Hi $NAME!"
+	</verb></tscreen>
+	<P> As a variant, you can get multiple values with read, this example may clarify this.
+	<tscreen><verb>
+		#!/bin/bash
+		echo Please, enter your firstname and lastname
+		read FN LN 
+		echo "Hi! $LN, $FN !"
+	</verb></tscreen>
+	
     </sect1>
 
     <!-- Arithmetic evaluation  -->    
@@ -611,7 +670,7 @@ Misc
     Getting the return value of a program
         <P> In bash, the return value of a program is stored in a special variable called $?.
 	<P> This illustrates how to capture the return value of a program, I assume that the directory
-	/dada does not exist. (This was also suggested by mike)
+	<it/dada/ does not exist. (This was also suggested by mike)
 	<tscreen><verb>
 	#!/bin/bash
 	cd /dada &> /dev/null
@@ -666,8 +725,26 @@ Tables
     <P> (4) __TO-DO__
     <P> (5) s1 is not null (contains one or more characters)
     <P> (6) s1 is null 
-
     </sect1>
+
+	<sect1>
+	String comparison examples
+	<p> Comparing two strings. 
+	<tscreen><verb>
+	#!/bin/bash
+	S1='string'
+	S2='String'
+	if [ $S1=$S2 ];
+	then
+	        echo "S1('$S1') is not equal to S2('$S2')"
+	fi
+	if [ $S1=$S1 ];
+	then
+	        echo "S1('$S1') is equal to S1('$S1')"
+	fi
+	</verb></tscreen>
+	</sect1>
+
     <!-- Arithmetic operators -->    
     <sect1>
     Arithmetic operators
@@ -703,7 +780,8 @@ Tables
 	 <P> sort 
 	 <P> bc   (more than a calculator)
 	 <P> cut  (edit columns)
-	 
+	 <P> tput (get information from the current terminal)
+ 
          <P> It it higly recommended to be familiarized with
 	  this programs (at least). There are tons of little 
 	  programs that will let you do real magic in a 
@@ -885,20 +963,24 @@ About the document
      Thanks to
      <P>
      <itemize>
-         <item> Nathan Hurst for sending a lot of corrections.
-	 <item> Jon Abbott for sending comments about evaluating arithmetic expressions.
-	 <item> Laurent Martelli for  translating this document to French (soon here the URL)
-	 <item> Felix Hudson for writing the <it/renna/ script
+        <item> Nathan Hurst for sending a lot of corrections.
+	<item> Jon Abbott for sending comments about evaluating arithmetic expressions.
+	<item> Laurent Martelli for  translating this document to French (soon here the URL)
+	<item> Felix Hudson for writing the <it/renna/ script
 
-	 <item> Mike (pink) made some suggestions about locating bash and testing files
+	<item> Kees van der Broek (for sending many corrections)
+	<item> Mike (pink) made some suggestions about locating bash and testing files
 	 
      </itemize>
      </sect1>
 	<sect1>
 	History
-	<p> v5 Added the redirection section
-	<p> v4 disapperd from its location due to my ex-boss and thid doc found it's new place 
-	at the proper url: www.linuxdoc.org
+	<p> Samples added on string comparison.
+	<p> v0.7 More corrections and some old TO-DO sections written.
+	<p> v0.6 Minor corrections.
+	<p> v0.5 Added the redirection section.
+	<p> v0.4 disapperd from its location due to my ex-boss and thid doc found it's new place 
+	at the proper url: www.linuxdoc.org.
 	<p> prior:  I don't rememeber and I didn't use rcs nor cvs :(
 	</sect1>