Create a bash file with the following script. When you will run the script, it will continue until the user presses any key. Create a bash file with the following script that will do different types of tasks based on the key pressed by the user.
The script will terminate when the user will press ESC key. This script will print the keys pressed by the user until ESC key is pressed. The script will take a server name as input and will try to ping the server in every 2 seconds. Hope, after practicing the above examples, you will be able to write the script in such way that can wait for any keypress and do the particular task based on the key pressed by the user.
I am a trainer of web programming courses. I like to write article or tutorial on various IT topics. We can take input in bash script by using various types of options with the read command.
Sometimes we need to write the script in such a way that the script will run until a specific key is pressed or the particular script will execute based on the specific key or the program will wait for the specific amount of time until any key is pressed.
How you can write bash script to wait for any particular key or any key to some tasks is shown in this tutorial by using different examples. Example 1: Create a bash file with the following script.
Addition" echo "2. Subtraction" echo "3. Fahmida Yesmin I am a trainer of web programming courses. View all posts.Review your favorite Linux distribution. Welcome to LinuxQuestions. You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features.
Wait Command in Linux
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Hi everyone Ayone here have an idea how to hang a bash script until previous command is finished? I an opening a gnome-terminal from a bash script and i need the current script to wait until gnome-terminal finishes its job example : Quote:. From the bash man page. Last edited by frankbell; at PM. Find More Posts by frankbell View Blog. Thanks for the replybut i already try that without success. Do you want the text to be displayed inside the actual gnome-terminal that you have launched?
It only takes a minute to sign up. I would like to create another for loop after the first one to continue for another For example. I would like for the first set of jobs to finish before starting the new set. But because of the nohup it seems that they are all run simultaneously. I have nohup because I remotely login to my server and start the jobs there and then close my bash.
Is there an alternative solution? You'll want to use the wait command to do this for you. You can either capture all of the children process IDs and wait for them specifically, or if they are the only background processes your script is creating, you can just call wait without an argument. For example:. If your goal with nohup is to prevent a remote shell exit from killing your worker processes, you should use nohup on the script itself, not on the individual worker processes it creates.
As explained herenohup only prevents processes from receiving SIGHUP and from interacting with the terminal, but it does not break the relationship between the shell and its child processes. Because of the point above, with or without nohupa simple wait between the two for loops will cause the second for to be executed only after all child processes started by the first for have exited.
If you insert something like the following code segment in between your two for loops, it might help. Of course, if your application Rscript has a chance of not completing successfully and lingering around, your second for loop may not have a chance to run.
Code segment above assumes, all processes with the identifier Rscript --vanilla will complete and disappear properly. Without knowing what your application does and how it runs, I have to rely on this assumption.
In the light of the comments, this would better suit your needs. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered.
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Asked 3 years, 7 months ago. Active 3 years, 7 months ago. Viewed 75k times. I have a bash script that looks like the following: script!
For example script! Search the manual for the wait builtin. Active Oldest Votes. For example:! ParanoidGeek ParanoidGeek 1 1 silver badge 4 4 bronze badges. A few points: If your goal with nohup is to prevent a remote shell exit from killing your worker processes, you should use nohup on the script itself, not on the individual worker processes it creates.
Server Fault is a question and answer site for system and network administrators. It only takes a minute to sign up. I want to use it in a bash script, so when the host is starting up, the script keeps on pinging and from the moment the host is available, the script continues The loop body is empty, with the null command " : " used to prevent a syntax error.
Update: I thought of a way to make Control-C exit the ping loop cleanly. This will run the loop in the background, trap the interrupt Control-C signal, and kill the background loop if it occurs:.
I know the question is old I use this when rebooting hosts to know when I can SSH back into them again. Since ping will respond for several seconds before sshd is started. Ping the target host once. Check if the ping succeeded return value of ping is zero. If host is not alive, ping again. The following code can be saved as a file and called with the hostname as argument, or stripped of the first and last line and used as function within an existing script waitForHost hostname.
The code does not evaluate the cause for failure if the ping does not result in a response, thus looping forever if the host does not exist. My BSD manpage lists the meaning of each return value, while the linux one does not, so I guess this might not be portable, that's why I left it out. You may remove sleep 1, it's only here to prevent any flooding problem in case where the host would be reacheable but ping would not exit with code 0.
Please see good options at stackoverflow. Here is a sample in bash, you will have to loop over the following code until it returns a successfull ping result.
See fping 1 for details. I've been using the following function. I like it because I can tell it to stop trying after a while:. In general I want to wait for my database or other server to come up, but I don't want to wait too long. The following code waits for 10 seconds, then sets the exit code if the server did not appear within the time limit.
If the server appears before the time limit, the loop will be short-circuited so the next bit of code can run.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to ping in linux until host is known?The Wait-Job cmdlet waits for PowerShell background jobs to finish before it displays the command prompt.Shell Scripting Tutorial-48: Sleep while you are at work
You can wait until any background job is complete, or until all background jobs are complete, and you can set a maximum wait time for the job. When the commands in the job are complete, Wait-Job displays the command prompt and returns a job object so that you can pipe it to another command.
You can use Wait-Job cmdlet to wait for background jobs, such as those that were started by using the Start-Job cmdlet or the AsJob parameter of the Invoke-Command cmdlet. Starting in Windows PowerShell 3. To enable Wait-Job to wait for jobs of a particular type, import the module that supports the custom job type into the session before you run the Get-Job cmdlet, either by using the Import-Module cmdlet or by using or getting a cmdlet in the module.
For information about a particular custom job type, see the documentation of the custom job type feature. This example shows how to use the Wait-Job cmdlet with jobs started on remote computers by using the Start-Job cmdlet. This example uses Wait-Job to determine whether a Get-Date command running as a background job on three different computers is finished. All of the jobs are named Date1.
The third command uses Invoke-Command to run Wait-Job. This command waits for the Date1 jobs on each computer to finish. This example uses the Any parameter of Wait-Job to determine when the first of many background jobs running in the current session are completed. It also shows how to use the Wait-Job cmdlet to wait for remote jobs to finish. The first command creates a PSSession on each of the computers listed in the Machines.
The command uses the Get-Content cmdlet to get the contents of the file. The Using scope modifier is introduced in Windows PowerShell 3. The fourth command uses Invoke-Command to run a Wait-Job command in the sessions.
It uses the Any parameter to wait until the first job on the remote computers is completed. This example shows how to use the Timeout parameter of Wait-Job to set a maximum wait time for the jobs running on remote computers. The Wait-Job command determines whether all of the commands have completed within 30 seconds. In this case, after 30 seconds, only the command on the Server02 computer has completed.
Wait-Job ends the wait, displays the command prompt, and returns the object that represents the job that was completed. This command identifies three jobs by their IDs and waits until any one of them are completed.The exit status value of wait command depends on the command indicated by the last operand specified.
When any process terminates abnormally then the exit status will be greater than and shall be different from the exit status values of other commands. If wait command detects any error then it returns any value from 1 to If the last process id is unknown then wait command exits with value How you can use wait command in Linux is shown in this tutorial. In the following script, wait command is executed after terminating the process.
After that wait command is executed with the process id of the terminated process. The output will show the process id of the terminated process.
In the following script, the function check is called by two argument values. It is discussed in the starting of the tutorial that if wait command executed successfully the exit value will 0 and if wait command detects any error then it will returns any value between 1 and After running the script, if you pass 0 as second argument value then wait command terminates successfully and if you pass any value more than zero then it terminates unsuccessfully.
Hope, this tutorial will help to learn the use wait command properly. There is another command in Linux, named sleep to wait for the certain amount of times but there are some differences between these commands. If you are interested to know about sleep command then you can visit this link. About the author Fahmida Yesmin I am a trainer of web programming courses. I like to write article or tutorial on various IT topics. When multiple processes are running in the shell then only the process id of the last command will be known by the current shell.
If wait command is executed this time, then it will be applied for the last command. If no process id or job id is given with wait command then it will wait for all current child processes to complete and returns exit status. Fahmida Yesmin I am a trainer of web programming courses. View all posts.Rules and Examples. Synthesis Issues.
Some tools support a single wait on statement as an alternative to a sensitive list in a "combinational process". Whats New in ' In VHDLa wait statement may have a label. It is a snapshot of the page as it appeared on Sep 4, GMT. The current page could have changed in the meantime. Learn more Text-only version. See LRM section 8.
The wait until form suspends a process until a change occurs on one or more of the signals in the statement and the condition is evaluated to be true. The wait on form is equivalent to a sensitivity list. These processes will behave identically: process A,B begin -- sequential statements end process; process begin -- identical statements wait on A,B; end process; The wait statement cannot be used: In a process with a sensitivity list In a procedure called from a process with a sensitivity list.
In a function In a procedure called from a function Wait for and wait are useful in behavioural models and test benches. Most logic synthesis tools only support a single wait until clock edge expression statement in a "clocked process". Wait forunconditional wait and wait statements in procedures are not supported. These processes will behave identically: process A,B begin -- sequential statements end process; process begin -- identical statements wait on A,B; end process. The wait statement cannot be used: In a process with a sensitivity list In a procedure called from a process with a sensitivity list.
In a function In a procedure called from a function. Wait for and wait are useful in behavioural models and test benches.