Basic Unix Commands

• Table of Contents
  
• MetaCharacters
• File Links
• File Management Commands
• File Access
• Owners & Groups
• Disk Statistics
• UNIX Online Help
• Sys Admin Tool: sash
• UNIX Floppy Disks
• UNIX File Systems: Unmounted Floppy
• UNIX File Systems: Mounted Floppy
• UNIX File Systems: Unmounted Floppy

• File name wildcard metacharacters

char	meaning
*	match any characters
?	match any single character
[	begin a character group
]	end a character group
-	denotes a character range
!	negate a character group
|	logical "or" between patterns
?(pattern)	match zero or one instance of pattern
*(pattern)	match zero or more instances of pattern
+(pattern)	match one or more instances of pattern
@(pattern)	match exactly one instance of pattern
!(pattern)	match any strings that don't contain pattern

• Examples:

ls p*.c
lists all files that start with p and end in .c

ls prog?.c
lists all files that start with prog followed by any one char and end in .c

ls prog+([0-9]).c
lists all files that start with prog followed by one or more digits and end in .c

ls prog*([0-9])@(.f|.c)
lists all files that start with prog, followed by zero or more digits, followed by .f or .c

• Definition:
• Filenames that refer to the same file. Used to reduce redundancy and duplication. Changes to one affects the other. Both refer to the same physical file on the disk. Created with the ln command. Displayed in the ls listing as a file type of l.
• lrw-rw-r-- 1 smith cs1044 104 Sep 12 19:54 note2
•  
• Two type of links:

Hard links

A direct pointer to a file. If the original file is moved the link remains valid. A file is accessible as long as any hard link to it remains.

Symbolic links

A pointer to a file name; can be used across file systems. If the original file is moved the link is invalid. Created with the -s option. Deleting the link does not delete the original file.


• [10]% ln ../dir2/proga prog1
• The above link command creates a
  second (hard link) file reference to proga.
  
• [11]% ln -s ../dir2/proga prog1
• Same effect as above command, except
  that a symbolic (soft) link is created.

• [12]% cp ../dir2/proga prog1
• cp (copy) command creates a separate file ‘prog1’. C anges made to one do not affect the other.
  
• [13]% cp ../dir2/* .
• Copies all files from parent/dir2 to the current dir.
  
• [14]% rm ../dir2/proga
• rm (remove) command erases the file. rm does not notify user of the action that has occurred. rm accepts a list of files to erase. rm *.c erases all of the C files, whereas rm * erases all of the files in the working directory. rm -i proga forces rm to query before erasing files.

†rm does not actually erase the file. rm removes the link to the file. When the last link to a file is removed UNIX then reclaims the file space (i.e., the blocks pointed to by the inode list are returned to the free list).

• [15]% mv prog? ../dir2
• mv (move) relocates the file(s) into the specified directory.
• [16]% mv prog1 progb
• mv is also used to rename a file leaving the location unaltered.

†mv is implemented as ln and rm. A new link is established and then the old link removed.

• Permissions
• File access permissions, (modes), can be changed with the command:
  
  chmod permissions file-list
  
  
• Permissions can be set for:

u user (owner)
g group
o others
a all users

• The 3 types of access:
  r read (view and copy access)
  w write (modify and erase access)
  x execute (allows cd access to directories)
  
  can be increased or decreased by referencing a class and adding (+) or subtracting (-) permissions.
  
  
• The file access permissions should be set to allow all users access on floppies:
  
  chmod a+rwx /sony/*
  
  
• Octal permission specification: the rwx access of each class are bits that are on (1) or off (0) and can be specified to chmod as 3 separate digits:
  
  chmod 777 /sony/*

• File Ownership
• To change the owner of a file:

chown new-owner filelist


• Required when transfering floppies between systems:
  
  chown -R guest /sony
  
  
• Recursive option -R changes the owner for all files in the directory and subdirectories.
  
  
• User Groups
• Users can belong to groups to facilitate file sharing.
  
• To change the group of a file:

chgrp new-group filelist


• May be required when transfering floppies between systems:
  
  chgrp -R guest /sony
  
  
• Recursive option -R changes the group for all files in the directory and subdirectories.

• [17]% df

Filesystem          Total    kbytes   kbytes     
node               kbytes      used     free   used    Mounted on
/dev/rz2a           19743     10387     7382    58%    /
/dev/rz2g          294518    248466    16601    94%    /usr

• disk free: displays amount of free space on all disks.
  
  
• [18]% du -a /usr/users/guest

1058    ./eps
11      ./cursed.p
3       ./permsrec.p
76      ./printscreen.ps
93      ./menu.ps
1       ./.Xdefaults
1247    .

• disk usage: displays the amount of space (1/2 K blocks) occupied by a directory plus all of its files and subdirectories. du -k shows usage in 1 K blocks.

• man command-name
• Online help is available on any command through the UNIX man (manual) utility, (/usr/man).
  
• [19]% man rm

 

• apropos - help on a general topic
• [20]% apropos copy
  
• type - where does a command live?
• [21]% type cp
  

cp is a tracked alias for /bin/cp


• which - where does a command live?
• [22]% which cp

/bin/cp

• System Adiminstration SHell
• SASH Commands

$ sash
SASH  System Administration Shell  Version 2.05
Type 'help' for command list.
sash> help
check       perform a filesystem check on the floppy
format      format the floppy for mounting (specify
            density as dd, hd, or ed)
halt        halt the system
help        display these helpful command descriptions
mount       mount a floppy
owner       change ownership to current user
quit        exit SASH
raw         format floppy for tar or cpio (specify
            density as dd, hd, or ed)
reboot      reboot the system
tarp        set permissions for tar or cpio
umount      synonym for 'unmount' command
unmount     unmount the floppy
untarp      reset permissions to normal after tar or
            cpio

• Before a disk may be used under UNIX it will need to be formatted and then ejected.
• At this point, for example, the following situation could be present:

• The file system that was created during formatting is a separate file system with initially only a root dir.

• Inserting the disk and mounting it would lead to the following state:

The floppy file system is attached to /sony and is now considered part of the total file system. The /sony dir can be used with any UNIX commands the same as any other dir:

$cp p* /sony

• Unmounting the disk now yields:
  

• Transport Concerns
• Files from mounted floppies, transported between machines, will not be accessible if the owner and group are not the same as on the machine on which they were created.
  

$ sash owner

• Sash can be used to change the owner of a mounted floppy.