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Full Discussion: shell programming assignment
Top Forums Shell Programming and Scripting shell programming assignment Post 302157650 by Jake777 on Friday 11th of January 2008 04:26:19 PM
Old 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.

403



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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mv(1)							      General Commands Manual							     mv(1)

NAME
mv - Moves files and directories SYNOPSIS
mv [-i | -f] [--] file1 file2 mv [-i | -f] [--] file1... directory mv [-i | -f] [--] directory1... destination_directory The mv command moves files from one directory to another or renames files and directories. STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: mv: XCU5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. OPTIONS
Overrides the -i option and any mode restrictions. (If both -f and -i are specified--for example, because an alias includes one of them--whichever appears last overrides the other.) Prompts you with the name of the file followed by a question mark whenever a move is to supersede an existing file. If the answer begins with y, or the locale's equivalent of a y, the move continues. Any other reply prevents the move from occurring. (If both -f and -i are specified--for example, because an alias includes one of them--whichever appears last over- rides the other.) Interprets all following arguments to mv as file names. This allows file names to start with a - (dash). DESCRIPTION
If you move a file to a new directory, mv retains the original file name. When you move a file, all other links to the file remain intact. In the second form, one or more files are moved to directory with their original file names. In the third form, one or more directories are moved to the destination directory with their original names. The mv command does not move a file onto itself. When you use mv to rename a file, the target file can be either a new file name or a new directory path name. If moving the file would overwrite an existing file that does not have write permission set and if standard input is a terminal, mv displays the permission code of the file to be overwritten and reads one line from standard input. If the line begins with y, or the locale's equivalent of a y, the move takes place and the file is overwritten. If not, mv does nothing with the file. When you use mv to move a directory into an existing directory, the directory and its contents are added under the existing directory. The LC_MESSAGES variable determines the locale's equivalent of y or n (for yes/no queries). If a mv operation fails, mv generally writes a diagnostic message to standard error, does nothing more with the current source file, and goes on to process any remaining source files. If the copying or removal of a file is prematurely terminated by a signal or error, mv might leave a partial copy of the file at either the source or the target path name. The mv program does not modify the source and target path names simultaneously; therefore, program termina- tion at any point always leaves either the source file or the target file complete. NOTES
[Tru64 UNIX] If the source is on a different file system than the destination, mv must copy the source to the destination's file system and then delete the source. The effect is equivalent to the following: rm -f destination && cp -pr source destination && rm -rf source The mv command might overwrite existing files. Specify the -i option last on the command line to cause the mv command to prompt you before it moves a file. EXIT STATUS
The following exit values are returned: All files were moved successfully. An error occurred. EXAMPLES
To rename a file, enter: mv file1 file2 This renames file1 to file2. If a file named file2 already exists, its old contents are replaced with those of file1. To move a directory, enter: mv dir1 dir2 This moves dir1 to dir2. It moves dir1 and all files and directories under dir1 to the directory named dir2, if the second direc- tory exists. Otherwise, the directory dir1 gets renamed dir2. To move a file to another directory and give it a new name, enter: mv file1 dir1/file2 This moves file1 to dir1/file2. The name file1 is removed from the current directory, and the same file appears as file2 in the directory dir1. To move a file to another directory, keeping the same name, enter: mv file1 dir1 This moves file1 to dir1/file1. To move several files into another directory, enter: mv file1 dir1/file2 /u/dir2 This moves file1 to /u/dir2/file1 and dir1/file2 to /u/dir2/file2. To use mv with pattern-matching characters, enter: mv dir1/* . This moves all files in the directory dir1 into the current directory (.), giving them the same names they had in dir1. This also empties dir1. Note that you must type a space between the * (asterisk) and the (dot). ENVIRONMENT VARIABLES
The following environment variables affect the execution of mv: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari- ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the for- mat and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES. SEE ALSO
Commands: cp(1), ln(1), rm(1) Functions: rename(2) Standards: standards(5) mv(1)
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