01-11-2008
shell programming assignment
I have a very tough shell program to do. Here is the assignment:
Write a non-interactive script that takes in any number of directory names as arguments and calculates and outputs the total number of blocks of disk space occupied by the ordinary files in all the directories. For example, the user would type:
assignment3 dir1 dir2 dir3 dir4
403
and the output is simply the number of blocks occupied by ordinary files in those directories. If, let’s say dir2 was not a directory and dir4 was inaccessible due to lack of permission say, then the program output (including errors) might be:
assignment3 dir1 dir2 dir3 dir4
assignment3: WARNING: dir2 is not a directory.
assignment3: WARNING: dir4 could not be accessed.
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The following script will find and output the number of blocks occupied by the filename supplied as an argument;
if test –e “${1}”
then
ls -sd ${1} | sed 's/^ *//' | cut -d' ' -f1
else
echo 0
fi
If the file given as an argument exists then ls will get the size in blocks and the filename and pass them to sed; sed will strip the leading spaces and pass it to cut; cut will extract and output the number of blocks. If the file given as an argument does not exist then 0 is output (a file that does not exist occupies no space).
This script will be placed in your home directory and named getblocks. You can use it in your script to get the number of blocks occupied by a file. Use it in your script in the following way (I am using a file called ‘file17’ as an example – in your program the filenames will be held in variables):
(( numblocks=$(getblocks file17) ))
This line will calculate the number of blocks occupied by a file called file17 and assign it to variable numblocks.
Your script should give sensible error messages and/or warnings where appropriate. For example, you should detect and report on the following possible errors or warnings:
1. no arguments given: ERROR – need to exit the program;
2. the argument being processed is not a directory: WARNING – no need to exit… just continue to the next argument;
3. the argument given names a directory that cannot be accessed (use ls command to determine this): WARNING - no need to exit… just continue to the next argument.
To tackle this assignment you will need to know:
1. how to capture the output of a command inside a script using ‘command substitution’; (see lab 7)
2. how to write a for loop that will process a list of files from a directory named in the argument list; (see lab 7)
3. how to write a while loop that will continue to process the arguments until they are all dealt with; (see lab 7)
4. how to create (and initialize) integer variables, and lowercase and uppercase string variables. (see lab 7)
5. how to do simple arithmetic using the (( )) command. (see lab 7)
6. how to check if a file is an ordinary file;
7. how to check if a file is a directory file.
8. how to write error messages, usage messages, and warning messages;
I just need some help in getting started on it.
Thank you.
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LEARN ABOUT ULTRIX
return
exit(1) User Commands exit(1)
NAME
exit, return, goto - shell built-in functions to enable the execution of the shell to advance beyond its sequence of steps
SYNOPSIS
sh
exit [n]
return [n]
csh
exit [ ( expr )]
goto label
ksh
*exit [n]
*return [n]
DESCRIPTION
sh
exit will cause the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of
the last command executed (an EOF will also cause the shell to exit.)
return causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command exe-
cuted.
csh
exit will cause the calling shell or shell script to exit, either with the value of the status variable or with the value specified by the
expression expr.
The goto built-in uses a specified label as a search string amongst commands. The shell rewinds its input as much as possible and searches
for a line of the form label: possibly preceded by space or tab characters. Execution continues after the indicated line. It is an error to
jump to a label that occurs between a while or for built-in command and its corresponding end.
ksh
exit will cause the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8
bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing
a trap, the last command refers to the command that executed before the trap was invoked. An end-of-file will also cause the shell to exit
except for a shell which has the ignoreeof option (See set below) turned on.
return causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value will be the
least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return
is invoked while not in a function or a '.' script, then it is the same as an exit.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
break(1), csh(1), ksh(1), sh(1), attributes(5)
SunOS 5.10 15 Apr 1994 exit(1)