Best way to learn UNIX and shell Programming Post: 302552669

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Top Forums Shell Programming and Scripting Best way to learn UNIX and shell Programming Post 302552669 by kermit on Monday 5th of September 2011 05:35:05 AM

09-05-2011

Registered User

Disclaimer: I am not a professional UNIX guy - I work in a completely different field.

From my perspective, the number one most helpful thing you can do is to be constantly coding. This is particularly helpful if you have a need (or at least desire) some particular behaviour in your system. For example, I had a buggy program, and sometimes would need to kill several instances of it. It was a pain to do a `ps -A` every time, and manually kill each instance of the process. So I made a one-line script that would do a ps -A, grep for the name of the particular process, parse and grab the pid from the first field, and then do a kill on those numbers. Over time, I polished and extended the script, adding functionality, and making the output a little more informative/easier to read.

Now there a few things to note here:

At the time, I did not know of pkill and friends, so I was basically reinventing the wheel. As I look back, that was OK, because I learned something while doing it. In fact, it is a decent way to learn. You basically take a known utility that you normally use, eg., pkill, or whatever, and re-implement it yourself. At first, your new program likely won't have all of the functionality of the full blown version on your system, but you can add that over time. This concept is also helpful in other areas, such as C programming. It is very instructive, for example, to make your own versions of the string library functions. Not for actual use necessarily, but for learning. (It is hard to beat the system versions, in terms of outright speed. If you already know enough to improve on the standard library, then my points here are basically moot.)
If the process of learning how to shell program seems to be coming slowly, remember to be patient with yourself, and stick with it. Everybody's situation is different. For my part, I am a slow learner (it seems), and I have been hacking away for years and am not nearly as far as others have gotten in the same time. If I was doing this for a living, I know I would be farther along, because a), I would be immersed in it, and b) I would (ostensibly) have other professionals to guide me when I was doing something that was not quite right. This is true of mostly any profession I think. There is a huge learning curve with this sort of thing - lots of nooks and crannies. Be patient!

So that is my two cents worth. Write lots of code. It would be preferable to be writing some useful little stuff which improves some particular situation of your own (as opposed to toy exercises, which initially can be somewhat helpful, but are ultimately limited in value). If you are like me, you likely want to grab an O'Reilly book on scripting, or something like that as well. Ask lots of questions as well.

kermit

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LEARN ABOUT DEBIAN

kill

KILL(1) 							   User Commands							   KILL(1)

NAME

       kill - send a signal to a process

SYNOPSIS

       kill [options] <pid> [...]

DESCRIPTION

       The  default  signal  for kill is TERM.	Use -l or -L to list available signals.  Particularly useful signals include HUP, INT, KILL, STOP,
       CONT, and 0.  Alternate signals may be specified in three ways: -9, -SIGKILL or -KILL.  Negative PID values may be  used  to  choose  whole
       process	groups;  see  the  PGID  column  in ps command output.	A PID of -1 is special; it indicates all processes except the kill process
       itself and init.

OPTIONS

       <pid> [...]
	      Send signal to every <pid> listed.

       -<signal>
       -s <signal>
       --signal <signal>
	      Specify the signal to be sent.  The signal can be specified by using name or number.  The behavior of signals is explained  in  sig-
	      nal(7) manual page.

       -l, --list [signal]
	      List signal names.  This option has optional argument, which will convert signal number to signal name, or other way round.

       -L, --table
	      List signal names in a nice table.

       NOTES  Your shell (command line interpreter) may have a built-in kill command.  You may need to run the command described here as /bin/kill
	      to solve the conflict.

EXAMPLES

       kill -9 -1
	      Kill all processes you can kill.

       kill -l 11
	      Translate number 11 into a signal name.

       kill -L
	      List the available signal choices in a nice table.

       kill 123 543 2341 3453
	      Send the default signal, SIGTERM, to all those processes.

SEE ALSO

       kill(2), killall(1), nice(1), pkill(1), renice(1), signal(7), skill(1)

STANDARDS

       This command meets appropriate standards. The -L flag is Linux-specific.

AUTHOR

       Albert Cahalan <albert@users.sf.net> wrote kill in 1999 to replace a bsdutils one that was not standards  compliant.   The  util-linux  one
       might also work correctly.

REPORTING BUGS

       Please send bug reports to <procps@freelists.org>

procps-ng							   October 2011 							   KILL(1)