lesson 7-creating and changing directories. overview using directories to create order. managing...
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Lesson 7-Creating and Changing Directories
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Overview
Using directories to create order.
Managing files in directories.
Using pathnames to manage files in directories.
Accessing files in remote directories.
Managing files from more than one directory.
Moving and removing directories and their contents.
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Using Directories to Create Order
A file is a collection of information stored electronically on
the hard drive of a system.
An inode contains all the information about each file,
including the location of the actual file on the disk.
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Using Directories to Create Order
The home directory.
Listing files in a directory.
Working with directories.
Distinguishing between files and directories.
Obtaining information about a directory or its contents.
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The Home Directory
The “pwd” command displays the path from root to the
user’s home directory.
The /etc/passwd file holds the user’s home directory path.
A file is created and listed in the current home directory by
default.
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Listing Files in a Directory
The “ls” command reads the names of the files listed in the
current directory, and then outputs those names.
Each file in the directory contains only the name of that file
and a number that leads to the inode for that file.
The “–i” option instructs ls to include the inodes in its output.
Inodes are small pieces of memory created on the hard disk
when it is formatted.
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Listing Files in a Directory
The inode has a list of addresses of the block on the disk
where the data that comprise the file is actually located.
It addresses up to 13 data blocks on the hard drive.
The first ten blocks addressed from the inode contains the
actual file data.
If a file is too large, additional blocks are allocated to fit the
data.
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Working with Directories
The “mkdir” command is used for creating a new directory.
Directories created in uppercase are listed first by the ls
command.
Each new directory created is called a subdirectory.
The “cd” or “change directory” command instructs the shell
to locate the directory listed as an argument.
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Working with Directories
The “pwd” command outputs the absolute path from the
top of the file system (root or /) to the current directory.
A path is a list of directory names separated by the / (slash)
character.
The topmost directory is called the root and is symbolized
by the first forward slash (/) in the pathname.
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Working with Directories
The vi editor can be used for creating a file within a
directory or subdirectory.
The cd command, without any directory name as an
argument, returns to the home directory.
The “–R” (recursive) option used with ls descends through
each subdirectory in the directory tree.
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Distinguishing between Files and Directories
The “ls –F” command displays directory names with a slash
appended at the end.
Filenames displayed with an asterisk (*) at the end are
executable files.
The “–C” option to ls instructs ls to make several columns in
the output instead of one.
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Obtaining Information About a Directory or its Contents
The “ls –l” command displays the permissions and owners
of files listed in a directory.
The “–d” option with ls command returns a listing of
information about the contents of the target directory.
The “ls –ld” displays the permissions of the directory, and
not the information about the files.
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Managing Files in Directories
Moving or copying files into a subdirectory.
Accessing a file in a subdirectory.
Avoiding mistakes when moving files into directories.
Renaming files.
Removing files from subdirectories.
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Moving or Copying Files into a Subdirectory
Moving a file or directory does not move the file
electronically.
The name and the inode number are erased from the
current directory and are written in the subdirectory.
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Moving or Copying Files into a Subdirectory
When a file is copied, a second electronic version is
created.
The copied file does not have the same inode number as
the original.
The copied file has its own inode, permission, and data
blocks containing the new files actual contents.
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Accessing a File in a Subdirectory
To access a file in a subdirectory:
Locate the inode number of the file.
Check the permissions on the directory.
Get the directory’s address from the inode.
Identify the inode associated with the file.
Read the files from the data blocks.
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Avoiding Mistakes When Moving Files into Directories
The mv utility takes two arguments.
The first argument is the name of an existing file.
The second argument is a new name assigned to existing
file, unless the second argument is a directory.
A slash at the end of the second argument interprets the
argument as a directory name.
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Renaming Files
The command to move a file listing from the current
directory to a new directory and also to change its filename
is mv filename subdirectory/newfilename.
Moving a file just moves its listing from one directory to
another.
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Removing Files from Subdirectories
The “rm” command can be used for removing files form a
directory or subdirectory.
After the rm command, the entry of the file is removed, and
the data blocks listed in the inode for that file are released.
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Using Pathnames to Manage Files in Directories
Accessing or creating a subdirectory.
Using pathnames with utilities.
Copying files into other directories using paths.
Using parent directory names.
Copying and moving multiple files to subdirectories.
Examining the full path from root to directories and files.
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Using Pathnames to Manage Files in Directories
Explicitly accessing a user’s home directory.
Including other users’ logins in directory paths.
Returning to the previous directory.
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Accessing or Creating a Subdirectory
Providing a full path to the cd command without any spaces
can access a subdirectory.
Pathnames are the mechanism used to tell the shell what
path to follow to access a file or directory not listed in the
current directory.
Remote directories can also be created by specifying the
relative or absolute pathname.
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Using Pathnames with Utilities
Pathnames can also be used as arguments to utilities.
A relative path can be specified for accessing a file without
changing the current directory.
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Copying Files into Other Directories Using Paths
Pathnames are particularly useful with the “cp” and “mv”
commands.
Any command that takes a filename or directory name as
an argument can be given an explicit pathname argument.
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Using Parent Directory Names
A single dot is used for referring to the current directory.
In a directory, the .. (dot-dot) is the listing for its parent
directory.
The parent directory is the directory located one level
above the current directory.
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Using Parent Directory Names
The parent directory lists the current directory’s name and
inode.
The . and .. are the two listings that get created when a
new directory is created.
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Copying and Moving Multiple Files to Subdirectories
The move and copy commands are usually used with only two
arguments.
The cp utility displays a usage error message when more than
two arguments are specified and the last argument is not a
directory.
In the cp command, if the third argument specified is a
directory, then the rest of the file arguments are copied into
the destination subdirectory.
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Copying and Moving Multiple Files to Subdirectories
The mv and cp commands can affect multiple files when
the last argument is a directory.
The .. (dot-dot) listing can be used in the mv command for
moving files into the parent directory.
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Examining the Full Path from Root to Directories and Files
A user can specify a directory’s location with the full path
from the top of the file system.
The full path starting at root identifies a file explicitly.
The pathname for every file describes a particular file
uniquely and absolutely.
The full pathname to a file is called its absolute pathname.
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Explicitly Accessing a User’s Home Directory
The “ls ~” command lists all filenames listed in the home
directory.
The C shell and all shells define the tilde (~) as the path to the
user’s home directory.
The shell replaces the tilde (~) with the value of the path to the
user’s home directory.
The shell replaces the tilde (~) in any command line with the
absolute path from root to the user’s home directory.
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Including Other Users’ Logins in Directory Paths
The “echo ~root” option displays the path to the home
directory of the user root.
The contents of the home directory of a user are displayed
if the user has appropriate permissions.
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Returning to the Previous Directory
The bash and ksh shells maintain the previous directory
path as the value of a variable.
The tcsh shell maintains a list of previous directories in a
list that can be accessed.
The value of the variable PWD is the path to the current
directory.
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Returning to the Previous Directory
An alternative way of specifying the previous directory on
many bash and ksh shells is to do it with a dash argument.
The exit command can be used for exiting from a child bash
or ksh to the login shell.
The “popd” command instructs the shell to move the
directory currently on the top of the list of directories that
are added to the list.
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Accessing Files in Remote Directories
A filename that includes no relative path defaults to the
current directory.
The ./ is the default relative path that is used.
Every file on the system has a unique pathname from /
(root).
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Accessing Files in Remote Directories
The “pwd” command displays the absolute path of the
present directory.
A path always starts at root (/) and includes the appropriate
subdirectories.
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Managing Files from More Than One Directory
A listing for a file in a directory is a link to the file.
The ls –l command at the start lists the number of data
blocks used by files and directories in the current directory.
In a long listing entry, or record, the information for each
file or directory is divided into seven fields.
The second field in each entry of a file indicates the number
of directories where the object is listed.
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Managing Files from More Than One Directory
Linking files:
The “ln” command can be used for linking a file to the current
directory.
The index card of each file keeps track of the number of
directories that list it.
Each instance of the file listed in a directory is one link.
Removing a file removes it from the directory listing.
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Managing Files from More Than One Directory
Linking files (continued):
The ln utility can be used to link multiple files at a time.
The “ls –il” command lists the current files with link count and
inodes.
The “–s” option to ln creates a file in the current directory that
contains information required to locate the linked file.
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Managing Files from More Than One Directory
Using symbolic links:
A symbolic link is a small file in a directory on one file system
partition that points to the correct file system and the correct
inode for the linked file.
In the long listing of the symbolic link, the initial character is an
“l” for directories and files.
An arrow and path at the end of the listing displays the actual
directory where the link points.
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Managing Files from More Than One Directory
Using symbolic links (continued):
The ln utility provides a “–d” option for the root user to create
hard links to directories.
Ordinary users cannot create directory hard links.
Ordinary users can create symbolic links to directories.
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Managing Files from More Than One Directory
The administrator can divide the hard drive into partitions
for installing the system.
The partition labeled / holds the core of the hierarchal
directory tree.
A partition is further divided into small pieces called data
blocks, which hold the actual data for the file.
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Managing Files from More Than One Directory
Each partition holds a single file system and has a set of
unique inode numbers for that partition.
The inode contains the whole of a file, including its
descriptive characteristics and the addresses of the blocks
where the file data resides.
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Moving and Removing Directories and their Contents
Renaming a directory only changes the name of the
directory, the inode number and its location remains
unchanged.
A directory can also be moved from a different location in
the hierarchal file structure without affecting the child
contents of the directory.
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The “rmdir” command is used for removing an empty
directory.
The “–r” option instructs the rm command to recursively
remove file.
Moving and Removing Directories and their Contents
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Summary
Files reside in one or more data blocks on the hard drive.
Each file in a directory is assigned a unique inode.
A directory is a special kind of file with very specific
contents, namely the names of files and directories, each
with its associated inode number.
The passwd file holds the location of a user’s home
directory.
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Summary
The mkdir command is used for creating remote directories.
The tilde (~) is interpreted as the user’s home directory.
The name .. (dot-dot) is interpreted as the parent directory.
The “rm –r dirname” command recursively removes the
contents of the directory specified.