HELP UNIX.COMMANDS                                 Aaron Sloman Nov 1995
                                                      Updated March 1996
                                            Updated (partly) 16 Oct 2011

Commands for unix/linux users.


CONTENTS

 -- Introduction
 -- Files and directories
 -- Changing file protection
 -- -- Using numeric specifications
 -- -- Using symbolic specifications
 -- -- Using umask
 -- Deleting and purging files
 -- Deleting files via editor commands
 -- Deleting files from Emacs
 -- Searching files
 -- Printing
 -- Displaying and killing your processes
 -- Ways of running commands
 -- Checking disk usage and quotas
 -- Miscellaneous
 -- -- Note on defining aliases, for "bash" and "ksh" users:
 -- Filename Patterns
 -- Online Unix manuals
 -- Online "unixhelp" tutor
 -- Tips directory and "advice" email list
 -- Other email lists
 -- Acknowledgements

-- Introduction -------------------------------------------------------

The file HELP * SHELL gives an overview of some of the important
features of Unix that most people need to know about.

Here a few of the standard Unix commands are listed. This file will
grow. Note that some commands are different on different Unix systems.
In particular SunOS and Berkeley Unix systems are slightly different
from Solaris and DIGITAL Unix.

Note: When a shell pattern is to be used, which may contain things
like "*" and "?" the examples below use the word PATTERN.

Note: In some cases the brackets "<" and ">" are used below to indicate
a type of argument to a command, e.g. ENTER man <name>. This should not
be confused with the use of "<" and ">" in a unix command to indicate
files to be used for input and output, as explained in the section on
ways of running Unix commands.

-- Files and directories ----------------------------------------------

display list of files             ls
                                  ls -l     (long listing)
                                  ls -lt    (reverse chronological order)

Show all files, including         ls -a
"dot" files                       ls -la

Show ONLY "dot" files             ls .??*

display contents of file          cat file

concatenate files                 cat file1 file2 file3 > bigfile
append to file                    cat file1 file2 file3 >> bigfile

display file with pauses          more file1
    Press space to continue
    Press B to go back, Q to quit

copy file                         cp file1 file2
                                  cp file1 file2 file... directory

compare files                     diff file1 file2

rename file                       mv file1 file2
move files                        mv file1 file2 file... directory

change file protection            chmod   (See MAN chmod)

create directory                  mkdir directory

change working directory          cd directory
                                  cd


-- Changing file protection -------------------------------------------

The command is "chmod" for "change mode". It is followed by some
flags, then a list of file names and directory names. The flags
can include "-R" meaning do it recursively including all sub
directories of directories specified.

The main type of flag indicates what sort of protection level you
want to set. The three man categories are

    r = file is readable
    w = file is writable or erasable
    x = file is executable

Each of these types of access can be given to three categories of users,

    u = the user (i.e. the person who owns the file, namely you)
    g = all people in the group the file belongs to
        (groups are not explained here)
    o = all others

Thus you can combine a specification of the people by using one or
more of the letters "u", "g", "o" and a specification of the type
of access by combining the letters "r", "w" "x", with a "+" or "-"
sign indicating whether access is to be allowed or removed. There are
also numeric codes specifying all these varieties of accessibility.

See MAN CHMOD for full details. Here are a few special cases

-- -- Using numeric specifications
Make files readable and writeable by
you and only readable by others         chmod 644 file1 file2 file3...
    Not to be used for directories
    or executable files.

Make executable files or directories
accessible by others, but writable only
by you                                  chmod 755 file1 file2 dir1 dir2 ...


-- -- Using symbolic specifications

Make sure file or directory is not
accidentally writeable by you or
anyone else                             chmod ugo-w  file1 file2 dir1 ...

Make files readable by you and members
of your group, but not anyone else
                                        chmod ug+r,o-r file2 file2 ...

Make files non-writeable by others      chmod go-w file1 file2 ...

Make all files in current directory
and its subdirectories non-writeable
by others                              chmod -R go-w  .

-- -- Using umask
In your .login or .csh file you can use a "umask" command to provide
a default set of permissions for all new files you create. The most
generally useful default is this

Let others read, but not alter files    umask 22

If you do that it is a good idea to have a protected directory, e.g.
your Mail directory into which you put things that you don't want others
to read. Then you don't need to remember to protect those files
individually. However you should never assume that anything on a unix
system is totally private. E.g. the system managers need to be able to
read everything.

If you are on a course with an assessed project you may have to ensure
that your top level directory and your project directory are readable by
others, so that your code can be run by examiners.


-- Deleting and purging files -----------------------------------------

You should always delete old files that you no longer need, e.g. files
from old courses, and also "backup" files created by editors. E.g. VED
creates backup files whose names end in "-", and Emacs creates backup
files whose names end in "~". Leaving unwanted files for long periods
causes inconvenience for other users (and yourself) when disk fill up
and people cannot create new files, and can add to the costs of running
the school by requiring us to purchase more disks than would otherwise
be necessary.

The following commands for removing files and directories should all be
used with extreme care. This is particularly the case where instead of a
specific file NAME you use a file PATTERN (see the section on filename
patterns below). The default Unix commands for deleting files do not
allow you to un-delete afterwards, though in some cases a file that you
accidentally delete can be retrieved from a backup tape. In this school
all files on the central file server are automatically backed up every
night. If you lose a file by accident, and wish to request that it be
retrieved, use the "support" command to log your request.

delete files                      rm file1 file2 ...
delete asking for confirmation    rm -i file1 file2 ...

delete a whole directory          rm -r directory
   (including all contents)

delete empty directory            rmdir directory

Note: for many users the "rm" command is set up so that it is equivalent
to "rm -i" i.e. you are asked to confirm for each file that it should be
deleted by typing "y" when prompted. You can bypass this by using the
command in the form "/bin/rm" which directly runs the rm (remove)
program so that it does not check. This can be much quicker, when you
are deleting lots of files, but it also can be dangerous.

-- Deleting files via editor commands ---------------------------------

Note: for VED users, there are some commands for deleting files directly
from the editor. See HELP * VED_PURGEFILES

    ENTER purgefiles PATTERN
        Lets you see a list of all files matching the pattern and then
        decide whether they should be deleted - all or none.

    ENTER purgefiles
        Equivalent to "ENTER purgefiles *-" for removing backup files.

    ENTER deletefile
        deletes the file you are currently looking at, removing it
        from both the VED buffer and the disk.

    ENTER purge
        This offers a range of options described in HELP * PURGE


-- Deleting files from Emacs ------------------------------------------

For Emacs users, there are also some commands for deleting files
directly from the editor. See M-x info dired

If you visit a directory (in the same way as you visit any other
file), then the command d marks files for deletion. You can v (view)
them first. The command x deletes files marked for deletion. There are
also lots of other commands. Do C-h m (help-mode) while visiting a
directory.


-- Searching files ----------------------------------------------------

find string in file(s)            grep string file1 file2 file3 ...
                                  egrep PATTERN file1 file2 file3 ...

    Where PATTERN may include pattern elements of the sort described
    in  MAN ED

-- Printing -----------------------------------------------------------

(Will depend on your installation.)

In these examples, replace the
word "printer" with the name of your
printer, e.g. lw22

print file                        lpr -Pprinter file
display print queue               lpq -Pprinter
delete file from print queue      lprm jobnumber
    See TEACH * PRINTING

-- Displaying and killing your processes ------------------------------

show my processes                 ps ux

The PID column printed out shows the PID, i.e. the Process IDentifier
for each process (a number). You need this to kill the process.

Kill a process                    kill pid
Send hangup signal                kill -1 pid
Irresistable kill                 kill -9 pid

Show top most active processes    top
    Type Q to quit

-- Ways of running commands -------------------------------------------

run a command in the background   command &

run background command with low   nice command &
    priority
To specify niceness 15,
using sh or bash or ksh           nice -15 command &
using csh, or tcsh                nice +15 command &

change priority of process
    with PID <pid>                renice -15 <pid>

run command with timing           time command arg1 arg2 ...

run command saving output in file command arg1 arg2 ... > file
run command with input from file  command arg1 arg2 ... < file
run command with intput and
    output files                  command > outfile < infile

feed output of one command        command1 arg1 arg2 ... | command2 ...
  through a pipe to another


-- Checking disk usage and quotas -------------------------------------

The "df" disk free command shows how much space is available and used
on various disks. On Solaris add the "-k" flag as shown below, to get a
nicer format and to get usage in kilobytes, which is more useful than
a measure in terms of disk blocks used.

display free disk space           df
                                  df -h     (nicer format on linux)

The "du" command shows disk usage of files or directories. On Solaris
it shows the amount of space in 0.5 Kbyte blocks, which is not very
useful. So by adding "-k" to the command, you get more useful
information.

show size (in MB) of a file or directory

                                  du -s FILE

show size of (disk space taken up by) all your top-level directories

                                  du -s ~/*


find out your current disk quota and total usage:
    (If you have file quotas set)

                                  quota -v


-- Miscellaneous ------------------------------------------------------

display date and time             date


start a new xterm window          xterm &
                                  xterm -geometry 80x34+400+400 &

start a new xterm on machine gromit
                                  xon gromit -access

define alias                      name='command1; command2....'

-- -- Note on defining aliases, for "bash" and "ksh" users:

In the "ksh" and "bash" shells, aliases are defined in the format

    name=string

and run by invoking $name:
e.g.

    myprocs='/usr/ucb/ps ux'

then
    $myprocs

For full details see MAN bash


-- Filename Patterns --------------------------------------------------

The following pattern elements may occur as PART of a file name
argument to a Unix shell command (e.g. grep, ls).

Unix will then find all files whose names match the patterns.

    *       match any sequence of characters
    ?       match only one character
    [0-3]   match one character, namely 0, 1, 2, 3
    [A-Z]   match any uppercase character
    [a-z]   match any lowercase character

Example 1. remove old VED backup files

    rm *-

Remove without asking questions

    /bin/rm *-

(If any of the files are write protected, you will be asked to
confirm that they should be deleted by typing "y"). To suppress such
questions (at your own risk) use the "-f" flag.

    /bin/rm -f *-

However, in a write-protected directory removal is impossible without
first changing the protection of the file or the directory.

Example 2. List all files ending in .p, showing latest first

    ls -lt *.p


-- Online Unix manuals ------------------------------------------------

get online Unix documentation     man name
                                  apropos string

    Where name is the name of some command, e.g. "ls", or "ps"
    and string can be any keyword.

report a problem or make a
   request to system manager.     support   (then follow instructions)

In VED, if you wish to see a comprehensive list of MAN files (depending
on your current setting for $MANPATH) you can do

    ENTER vman

And then when it invites you to choose from options press "*". You will
then get a list of directories and then a list of the MAN files in each
directory. You can view one by putting the VED cursor on the name and
then doing "ENTER vman" again. This is one way to browse to find out
what is available on the unix system, without ever leaving the editor.
(If it doesn't work, for some examples, just try "ENTER man <name>",
where <name> is the name of the file you are interested it, leaving
out any suffix like ".5" or ".3x"

-- Online "unixhelp" tutor --------------------------------------------

There is a very useful online Unix tutor, developed at Edinburgh
University, which can be used with a World Wide Web browser.

    http://www.cs.bham.ac.uk/research/projects/poplog/cas-ai/unixhelp.html

The simplest and fastest browser is lynx, which displays no pictures,
and does not use the mouse, and can be used over a dial-up line as it
does not require the X window system. If you start lynx, you use the
space bar to read the next screenful of the current file, the "b"
character to go back a screenful. Use the UP and DOWN arrows to move
to the next or previous link. Use the RIGHT arrow to follow a link and
the LEFT arrow to return to the previous file. Use "q" to quit.

Warning: do not believe everything you read in the tutor. There are some
mistakes, which I assume will be corrected eventually.

-- Tips directory and "advice" email list -----------------------------

(For users at Birmingham.)

    /bham/doc/tips/
        At Birmingham this directory has a number of files contributed
        by users, some of which have tips regarding Unix commands and
        "shell" scripts. On the CS Unix network only.

If you have problems about unix commands email "advice" for help. Do not
email "support" simply to ask for advice. If you would like to have
yourself added to the 'advice' email list, so that you see the questions
that get asked and the answers given, send an email message


-- Acknowledgements ---------------------------------------------------

Thanks to Mark Ryan and Brian Logan for checking the first draft of this
file and suggesting improvements and additions.

Please report errors or infelicities to
    Aaron Sloman
    http://www.cs.bham.ac.uk/~axs


--- $poplocal/local/help/unix.commands
--- Copyright University of Birmingham 1996. All rights reserved. ------