Introduction to UNIX

1
Introduction to UNIX

• D. UNIX File Structure

2
UNIX File System

• Performance Objectives
• 1. Identify types of Files (file)
• 2. Diagram the relationship of Files and
  Directories
• 3. Navigate the UNIX Directory Structure (cd,
  pwd)
• 4. Identify pathnames Absolute (/) and Relative
  (. .. )
• 5. Define file naming conventions
• 6. Make and remove directories (mkdir, rmdir)
• 7. List files and directories and their
  attributes (ls)

3
Types of Files

• Documents (ordinary files)
• Directories (help organize other files)
• Commands
• Special files - pipe
• Hidden files (dot)
• Devices

4
Relation of Files Directories

• Root is like a file cabinet.
• A directory is like a file drawer
• A subdirectory is like a folder within a drawer.
• A path is a list of directories subdirectories
  from root to a specific file or subdirectory.

Root
/
Directories
Files
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UNIX Directory Structure

• At login, you are in your home directory.
• This is your current working directory.
• All files and directories below your home
• directory usually belong to you.
• You change your working directory by
• changing to another directory (cd).

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Pathnames

• Absolute Pathname
• shows the absolute position of a file
• or directory in the hierarchy
• /home/user2/bif/docs
• begins with a slash (/) and
• describes how to get to the file from the root.

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Pathnames

• Relative Pathnames
• Describes how to get to a file from your current
  working directory.
• Special characters represent directory locations.
• home directory chidhkra
• current directory . cp chidhkra/file
  .
• parent directory .. cp chidhkra/file ..

8
Filesystems

• A file is identified by
• Combining directory pathnames
• To the filename
  /usr/local/meeting

root
/
usr
files
local
meeting
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Naming Files

• Filenames may be 1 to 255 characters
• UPPER and lowercase,
• numbers,
• other ASCII characters,
• except special Shell characters,
• control characters and the space.

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Filename DON'TS

• Don't begin a filename with a dot (.)
• Don't use any of the following characters
• ? lt
• \ gt
• ( ) ' -
• " !
• /

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Examples of UNIX File Names

• status.memo
• casey_mt
• 1.2.3
• chapter1

12
Hidden Files (dot)

• Used to establish your environment
• .cshrc .login
• .pinerc .forward
• Must use ls -a option to view
• Always in home directory
• (some exceptions)

13
Naming Conventions

• Programs like make, cc, and sccs use a default
  conventions to name files generated
• ltfgt.o Binary Compiler Output
• ltfgt. i C preprocessor Output
• ltfgt.c C/C language source code
• ltfgt.f Fortran source code
• ltfgt.mk Makefiles
• s.ltfgt SCCS files
• a.out executable name

• ltfgt.j FPP output files
• ltfgt.a AR or BLD files
• ltfgt.Z compressed files (use
• uncompress)
• ltfgt.gz gzipped files (use gunzip)
• ltfgt.tar tape archive (use tar)
• ltfgt.l compiler listings

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Identifying File Content

• The command file identifies file content
• host file passwd
• passwd ascii text
• host file dhk/
• PSaddress PostScript document
• acl directory
• address ntroff, tbl, or eqn input
  text
• adv.fil ascii text
• cfs.size executable shell script
• dip shell commands

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Directory Commands

• mkdir making a directory
• cd changing your working directory
• pwd printing your working directory
• ls listing the contents of a directory
• rmdir removing a directory

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Directory Commands - mkdir

• Make directory under current working directory
• host mkdir docs
• Make directory under subdirectory
• host mkdir docs/index
• Make directory and subdirectory
• host mkdir docs docs/index
• Make directory using absolute path
• host mkdir /usr/tmp/abc

User1
(cwd)
docs
User1
(cwd)
docs
index
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Common Error Messages

• mkdir dirname File exists
• mkdir dirname Permission denied

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Directory Commands - cd
userx

• host cd docs
• host cd /usr/tmp/abc/docs
• host cd abc/docs
• host cd
• host cd ..

docs
/usr
tmp
abc
docs
abc
docs
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Common Error Messages

• pathname No such file or directory
• pathname Permission denied

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Directory Commands - pwd

• Determining the current working directory
• host pwd
• /scc/users/chitspit/bif
• where
• / root
• scc/ file system followed by the
  delimiter (/)
• users/ subdirectory of scc
• chitspit/ directory followed by the
  delimiter (/)
• bif current working directory

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Directory Commands - ls
cwd

• host ls
• bin mbox remodel
• complex.f outdis test
• host ls -sF (Multiple options may be
  specified)
• 15 bin/ 256 mbox 3 remodel/
• 34 complex.f 6 outdis_at_ 1 test
• host ls chitspit/bin
• au clst prod show xref

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Directory Commands - ls

• The long list provides additional file
  information
• host ls -l
• total 31
• drwxr-xr-x 2 dhk 512 Oct 23 1985 bin
• -rw-r--r-- 1 dhk 129 Nov 20 1985 comp
• -rw------- 1 dhk 129 Jul 2 1005 mbox
• -rw-r--r-- 1 dhk 4291 Jun 16 1418 outdis
• drwxr-xr-x 2 dhk 512 Jan 22 1107 remod
• -rwxr-xr-x 1 dhk 10291 Mar 19 1255 test

List alphabetized
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List Hidden Files ls -a

• The -a option lists all files in a directory
• host ls -a
• . .login mail test
• .. bin public_html
• .cshrc complex.f remodel

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Directory Commands - rmdir

• The rmdir command removes directories.
• host rmdir bif/docs
• Directory must be empty.
• Common error messages
• rmdir docs Directory not empty
• rmdir /scc/users/abc/docs Permission denied

userx
bif
docs
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End of Module

• Complete UNIX File Structure
• Exercises