I currently got the task of programming a UNIX Shell for practice. The functionality is as follows:
1. Entering commands with the keyboard. Enter stops the input and creates a process which should start any program
2. the shell waits for termination of each command before another command can be accepted
3. parameters should be extracted and correctly delivered to the specific programm
4. "logout" ends the shell (more of that later)
5. commands which have an '&' appended should be executed in the background. new commands can be entered thereafter
-> commands are not to be hardcoded
6. entering CTRL-C should deliver the currently running foreground process the signal SIGINT (not the shell)
7. entering CTRL-Z should deliver the currently running foregruond process the signal SIGSTP
8. implement a command "fg" that brings back a process back to the foreground which has been stopped by CTRL-Z
9. implement a command "bg" that lets a stopped process (by CTRL-Z) run again in the background
10. the shell can only be terminated if all background processes have been terminated, else give an error message, and make sure there should not be any zombie processes
I already started doing some of the tasks but I'm terribly unsure of how to exactly handle processes, it's very new to me. I would be delighted if someone could give me a more or less simple solution, so I can get the picture of it.
Hi all,
Can anyone provide me any checklists or a list of steps I should follow before executing my scripts.
Could also tell me if there are any other standards to be followed while shell programming like naming conventions for variables etc.
Your help would be much appreciated.
Regards,... (2 Replies)
Hi,
Iam using split command to split the files.
Splitted files will be named as xaa
xab
xac
xad etc.
Directories will be test1,test2,test3.....
Now i want to select the splitted files one by one and have to place in test directories.
can anybody give the soulution??? (2 Replies)
Hi,
i want to read a full file.
If i want to split the file and by reading parralel each, i can save the time.
Can any body give me the suggesion??
ia m using this function to read a file and using that i have to grep in another file. since the file 1 is huge it is taking lot of time.
... (3 Replies)
Hi,
I am looking for a PDF or an e-book which can show in details how to do Shell Scripting or Programming. Can anybody provide me with a link to such a tutorial? I have downloaded some tutorials but they show only basics and not give any in-depth study material.
I am using Red Hat Linux... (2 Replies)
Hi Gurus
I am very new to Unix Shell Prog. I have a file in format
Q1 Dirname-FileName Score Remarks
i.e. containing columns separated by space. I want to read Column 1 and 2 and then join them to make a string that would be a path to a file. I will use this string to fetch the files and... (4 Replies)
Hi guys
i have two different line
input
M5.7&a : M5 minimum density is 20%, maximum density is 80%,
DENSITY PERM=M5.8&a(180) ......... 6 violations found.
M6.7&a : M6 minimum density is 20%, maximum density is 80%,
DENSITY A=M6.8&a(180) ......... 6 violations found.
need... (2 Replies)
Guys,
What do you think is the best way to learn UNIX and shell scripting?
** I keep on searching tutorials online, where I loose most of my time :(
Let me know the way you learnt the UNIX concepts, your replies might help me learn more.
Thanks a ton:b: (2 Replies)
1. The problem statement, all variables and given/known data:
Hello! :)
I currently got the task of programming a UNIX Shell for practice. The functionality is as follows:
1. Entering commands with the keyboard. Enter stops the input and creates a process which should start any program
2.... (0 Replies)
Discussion started by: DarkDan
0 Replies
LEARN ABOUT PHP
wait
wait(1) User Commands wait(1)NAME
wait - await process completion
SYNOPSIS
/bin/sh
wait [pid...]
/bin/jsh /bin/ksh /usr/xpg4/bin/sh
wait [pid...]
wait [ % jobid...]
/bin/csh
wait
DESCRIPTION
The shell itself executes wait, without creating a new process. If you get the error message cannot fork,too many processes, try using the
wait command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many
active foreground processes. There is a limit to the number of process IDs associated with your login, and to the number the system can
keep track of.
Not all the processes of a pipeline with three or more stages are children of the shell, and thus cannot be waited for.
/bin/sh, /bin/jsh
Wait for your background process whose process ID is pid and report its termination status. If pid is omitted, all your shell's currently
active background processes are waited for and the return code will be 0. The wait utility accepts a job identifier, when Job Control is
enabled (jsh), and the argument, jobid, is preceded by a percent sign (%).
If pid is not an active process ID, the wait utility will return immediately and the return code will be 0.
csh
Wait for your background processes.
ksh
When an asynchronous list is started by the shell, the process ID of the last command in each element of the asynchronous list becomes
known in the current shell execution environment.
If the wait utility is invoked with no operands, it will wait until all process IDs known to the invoking shell have terminated and exit
with an exit status of 0.
If one or more pid or jobid operands are specified that represent known process IDs (or jobids), the wait utility will wait until all of
them have terminated. If one or more pid or jobid operands are specified that represent unknown process IDs (or jobids), wait will treat
them as if they were known process IDs (or jobids) that exited with exit status 127. The exit status returned by the wait utility will be
the exit status of the process requested by the last pid or jobid operand.
The known process IDs are applicable only for invocations of wait in the current shell execution environment.
OPERANDS
The following operands are supported:
One of the following:
pid The unsigned decimal integer process ID of a command, for which the utility is to wait for the termination.
jobid A job control job ID that identifies a background process group to be waited for. The job control job ID notation is applicable
only for invocations of wait in the current shell execution environment, and only on systems supporting the job control option.
USAGE
On most implementations, wait is a shell built-in. If it is called in a subshell or separate utility execution environment, such as one of
the following,
(wait)
nohup wait ...
find . -exec wait ... ;
it will return immediately because there will be no known process IDs to wait for in those environments.
EXAMPLES
Example 1: Using A Script To Identify The Termination Signal
Although the exact value used when a process is terminated by a signal is unspecified, if it is known that a signal terminated a process, a
script can still reliably figure out which signal is using kill, as shown by the following (/bin/ksh and /usr/xpg4/bin/sh):
sleep 1000&
pid=$!
kill -kill $pid
wait $pid
echo $pid was terminated by a SIG$(kill -l $(($?-128))) signal.
Example 2: Returning The Exit Status Of A Process
If the following sequence of commands is run in less than 31 seconds (/bin/ksh and /usr/xpg4/bin/sh):
sleep 257 | sleep 31 &
jobs -l %%
then either of the following commands will return the exit status of the second sleep in the pipeline:
wait <pid of sleep 31>
wait %%
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of wait: LANG, LC_ALL, LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), jobs(1), ksh(1), sh(1), attributes(5), environ(5), standards(5)SunOS 5.10 12 Dec 1997 wait(1)