Bourne Shell: Chapter 6c

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6.7  sort: Sort a File

The sort utility sorts line of all the named files together and
writes the result to standard output. The standard input is used
if - is used as a file name or no input files are specified.

Comparisons are based one or more sort keys extracted from each
line of input. There is only one key by default, that's the entire
line, and ordering is lexicographic by bytes in machine collating
sequence.


                                                                
    Command format: sort [-cmu][-ooutput][-ykmem][-zrecsz]     
                         [-dfiMnr][-btx][+pos][-pos2][files]   
                                                               
     See on-line manual for options etc.                       
                                                                


The easiest way to use sort is to add it at the end af a pipeline.
What does the following command line accomplish:

Sample session:


                                                               
   $grep '[45]' phone.lis | sed 's//73/' | sort 
   Benson, Sam         734-5587                                
   StClair, Fred       734-6122                                
   Stair, Rich         735-5972                                
   $                                                           

 
The grep command will select only those records that have a 4 of 
a 5 in the phone number, those records are then sent to sed which
will add "73" just after the tab character, then the records are
sent to sort and put in alphabetical order. Notice that there is
a problem here, should StClair come before Stair in an alphabetical
listing? The answer is NO. Why did this happen? It occurred because
of the collating sequence for the default sort.

This can be fixed by specifying some options on the call to the
sort utility. Here are some options for sort. Let's see if we can
determine how to remedy the problem discovered in the default sort.


Sort options:

     -f   Fold lower case into upper case
     -r   Reverse the sort from highest to lowest
     -b   Ignore leading blank spaces
     -d   Dictionary sort - ignore non alphanumeric characters
     -m   Merge two sorted files together
     -n   Sort the list as numbers not digit characters

Notice the -f options folds lower case into upper case. This option
will make the sort for our problem work correctly. Here's the
sample.

Sample session:
                                                                 
        
             
   $grep '[45]' phone.lis|sed 's//73/'|sort -f      
   Benson, Sam         734-5587                                             
   Stair, Rich         735-5972                                             
   StClair, Fred       734-6122                                             
   $                                                                        

 
The sort can also be directed to use only a portion of the line as
a sorting key versus the entire line. The utility will
automatically break each line into fields at whitespace delimiters.
You can use a character other than whitespace by using the -t
option. The fields are set up like this:


        0     1        2
      /----|/---|/-------------|
     Adams, Fran         2-3876

   In order to sort by the second field here is the sort command
to enter.
 
Sample session:


    $sort +1 phone.lis                                         
    Adams, Fran        2-3876                                  
    StClair, Fred      4-6122                                  
    Smith, Joan        7-7989                                  
    Stair, Rich        5-5972                                  
    Benson, Sam        4-5587                                  
    Jones, Ted         1-3745                                  
    $                                                          


Here's a sample of a sort on the 3rd field.

Sample session:


     $sort +2 phone.lis                                        
     Jones, Ted        1-3745                                  
     Adams, Fran       2-3876                                  
     Benson, Sam       4-5587                                  
     StClair, Fred     4-6122                                  
     Stair, Rich       5-5972                                  
     Smith, Joan       7-7989                                  
     $                                                         


A sort can also be performed by a character position within a
field. Here's the sample.

Sample session:


    $sort +2.4 phone.lis                                       
    StClair, Fred           4-6122                             
    Benson, Sam             4-5587                           
    Jones, Ted              1-3745                             
    Adams, Fran             2-3876                             
    Stair, Rich             5-5972                             
    Smith, Joan             7-7989                             
    $                                                         


Note:     The first character of a field is the delimiter for that
          field        

6.8  What Other Useful UNIX Tools are Available

As stated from the beginning, one of the maxims used to develop
UNIX was that tools would continue to be developed. Here is a  
list of tools that might be of interest to you.                  

  
    UNIX Tool         Description                              
                                                               
    comm           Compares two sorted file and reports        
                   differences                                 
                                                               
    cut            Select columns or fields from lines in a    
                   field (System V only)                       
                                                               
    diff           Report the differences between two files    
                                                               
    join           Join lines in two files that contain a      
                   common field                                
                                                               
    pg             Show files (or standard input) on a terminal
                   a screen at a time                          
                                                               
    od             Print the numeric equivalent of a file's    
                   content                                     
                                                              
    tail           List end of files (or standard input) on    
                   standard output                             
                                                               
    tee            Sends standard input to two different places
                                                               
    tr             Transforms all occurrences of one character 
                   into another                                
                                                               
                                                               
    wc             Count the characters, words, and lines in a 
                   file                                        
   

6.9  Archiver and Library Maintainer
                                                                 
This command will maintain groups of files combined into a single
archive file.  The main use of ar is to create and update library
files as used by the link editor.  It can also be used for any
other similar purpose.  The file header consists of printable ASCII
characters.  If the archive consists of printable characters, then
the entire archive is also printable.

The format for the ar command is as follows:
                                                                 
 Command Format:  ar key [posname] afile [name]...             
                                                               
 Unlike command options, the command key is required.  The key,
 usually a - sign, is formed with one of the following letters 
 drqtpmx.  Arguments to the key are made from one or more of   
 the following set, vuaibcis.  See Appendix I for a complete   
 list of command keys.                                         
                                                               
 posname is an archive member name used as a reference for     
 positioning other files in the archive.                      
                                                               
 afile is the name of the archive.                             
                                                              
 name[s] are the constituent files in the archive.             
 
                                                               
To illustrate how to create and use an archive file, we will use
the "C" program called main.c and the two functions, funct1.c and
funct2.c.  First, create the object files that we intend to put
into the archive file.

Sample Session:


 $cc -c main.c funct1.c funct2.c                               
 main.c:                                                       
 funct1.c:                                                     
 funct2.c:                                                     
 $ls -C *.o                                                    
 funct1.o funct2.o main.o                                      
 $                                                             


Remember the -c option will not produce an executable module, but
it does create the object modules.  These object modules are file
files that we will place into an archive.

6.9.1  ar: Creating an Archive File with Object Modules

In this call to ar, we will use the r command key which will
replace the named files in the archive.  The v option will give a
verbose file-by-file description of the making of the new archive
file.

Sample Session:


 $ar rv functs.a funct1.o funct2.o                             
 a - funct1.o                                                  
 a - funct2.o                                                  
 ar: creating functs.a                                         
 $                                                             


The name of the new archive file is functs.a.  The files that have
been added to that archive are funct1.o and funct2.o.  The file
protections for the new archive file are rw-r--r--.



6.9.2  ar: Verifying the Contents of the Archive File

The key command to list the table of contents is t.  The t command
will print a table of contents of the archive file.  When the v
option is used with the t command it will give a long listing of
all information about the files.

Sample Session:


 $ar tv functs.a                                               
 rw-r--r--    115/    200 448 Sep 27 09:56 1990 funct1.o       
 rw-r--r--    115/    200 448 Sep 27 09:56 1990 funct2.o       
 $                                                             


This output shows that there are two members in this archive file,
namely, funct1.o and funct2.o.

The protections of these files is:

     owner - read and write
     group - read
     other - read

The fields are, left to right, the file protections, owner, group,
size (in bytes), creation date and time, and finally the name of
the constituent.

6.9.3  ar: Removing Duplicate Object Files


Once the archive has been created and verified, the object files
in your directory can be deleted.  This can be accomplished with
the rm command.

Sample Session:


 $rm funct?.o                                                  
 $                                                             


The question mark (?) is a wildcard that stands for any single
character.  The files funct1.o and funct2.o no longer exist in your
subdirectory.

6.9.4  ar: Compiling Main and Archive Files


Now that the object files, funct1.o and funct2.o, are in the
archive file functs.a you, can link them with main.o in the
following manner.

Sample Session:


 $cc -o new_hello main.o functs.a                              
 $ls -la new_hello                                             
 -rwxr-xr-x  1 teacher class  17570  Sep 27 12:58 new_hello    
 $                                                             




Workshop 6

This workshop will reinforce your understanding of the ideas
presented in Chapter 6. Login to the Multimax using the username
and password given to you by the instructor.  Each student is to
complete the entire workshop.

DESK EXERCISES 


     1.   What is a UNIX process?


     2.   When a command is given to the Shell it will fork a    
     child process to execute the command.

                      True/False

     3.   What is a process identification number (PID)?


     4.   What is the name of the Shell variable that contains   
     the current PID?


     5.   What is the UNIX command to find the PIDs associated   
     with the controlling terminal? What option is needed to     
     get detailed information?


     6.   What does the UNIX command grep do?


     7.   What do the following regular expressions represent?

               ^Ba

               .*

               BB*

               J*

               [0-9]*$

     8.   What does the UNIX command sed do?


     9.   What does the UNIX command awk do?


     10.  What does the UNIX command sort do?


     11.  What is the main use for the UNIX command ar?


     COMPUTER EXERCISES

     Use the phone.lis database file to answer the following
     questions.


     12.  "I want to find all the phone numbers that begin with a
           4 and end with a 2"


     13.  "I can't remember the name but I believe the last name
           starts with an S and the first name with an F"


     14.  Find all the people with 3 character first names.


     15.  Write a grep command that finds all the phone numbers
          that don't begin with a 4, 5, or 6.


     16.  Write a grep command that finds all entries beginning
          with J-Z and ending with a 2 or 5.


     17.  Put a 23 in front of every phone number. (Hint:sed)
     

     18.  Replace the first name with the person's first initial
          and a period.


     19.  Task: A new phone system has been installed and people
          with phone extensions beginning with 4 or 5 now have a
          new prefix: 73. Create a file of only the people with
          the new phone numbers.


     20.  Print out the phone list showing last name and first   
          name in the following format and sorted by last name.

                    First name  Last name


        That's enough, don't you think?
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