Exec pipe

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. It only takes a minute to sign up. With this command I expected the output of the script to be written into the log file with timestamps from the ts command. That does actually not happen, the output is written without any timestamps, other than that i also tried to do this:. With pipe components, I can only see it saving a fork with the zsh shell but only if applied on the last pipe component cmd1 exec cmd2and that means zsh no longer waits for the other pipe components.

Here, you're not redirecting the python script stderr to tsthough you are sending it to the log file. You'd probably want:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Pipe inside exec command won't work Ask Question. Asked 2 years, 11 months ago. Active 2 years, 11 months ago. Viewed 2k times. Any thoughts on why this happens and a possible solution would be much appreciated, thank you.

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Bash exec builtin command

I didn't write the script i just wanted to modify it in order to add the time stamps to the log file. That's an amusing construction. But it seems to work. KamilMaciorowski, the first part of a pipe runs in a subshell, so exec there just replaces that subshell. Not that it probably matters much, but the pipe will still be set up.

Active Oldest Votes. Sign up or log in Sign up using Google.As an example, let's say that you want to add a --log option to your script and if the user specifies it you want all the output to go to a log file rather than to the stdout.

Fork() system call tutorial

Of course, the user could simply redirect the output on the command line, but let's assume there's a reason why that option doesn't appeal to you. So, to provide this feature in your script you can do:.

The if statement uses test to see if file descriptor number one is connected to a terminal 1 being the stdout. If it is then the exec command re-opens it for writing on the file named log. The exec command without a command but with redirections executes in the context of the current shell, it's the means by which you can open and close files and duplicate file descriptors.

If file descriptor number one is not on a terminal then we don't change anything. If you run this command you'll see the first echo and the last echo are output to the terminal.

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The first one happens before the redirection and the second one is specifically redirected to stderr 2 being stderr. So, how do you get stderr into the log file also? Just one simple change is required to the exec statement:. Here the exec statement re-opens stdout on the log file and then re-opens stderr on the same thing that stdout is opened on this is how you duplicate file descriptors, aka dup them.

Note that order is important here: if you change the order and re-open stderr first i. Perhaps mainly as an exercise, let's try to do the same thing even if the output is not to the terminal.

What we want to do is manipulate things so that it appears that the following command was executed instead:. This just pipes exec's output to tee, and since exec doesn't produce any output in this instance, tee simply creates an empty file and exits. You might also think that you can try some dup-ing of file descriptors and start tee in the background with it taking input from and writing output to different file descriptors.

And you can do that, but the problem is that there's no way to create a new process that has its standard input connected to a pipe so that we can insert it into the pipeline although see the postscript at the end of this article. If we could do this, the standard output of the tee command would be easy since by default that goes to the same place the main script's output goes to, so we could just close the main script's output and connected it to our pipe if we just had a way to create it.

So are we at a dead end? Ahhhh no, that would be a different operating system you're thinking of. The solution is actually described in the last sentence of the previous paragraph.

We just need a way to create a pipe, right? Well let's use named pipes. Here, if the script's stdout is not connected to the terminal, we create a named pipe a pipe that exists in the file-system using mknod and setup a trap to delete it on exit.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. It only takes a minute to sign up. You don't need to use find for this at all; grep is able to handle opening the files either from a glob list of everything in the current directory:.

This searches recursively for all. Output looks like just ran one today :. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to run find -exec? Ask Question.

exec pipe

Asked 8 years, 11 months ago. Active 12 months ago. Viewed k times. I'd like to find the files in the current directory that contain the text "chrome".

Gilles 'SO- stop being evil' k gold badges silver badges bronze badges. Related: unix. Active Oldest Votes. To get a file list instead add use grep -ls inside of the find construct. Caleb Caleb Good points Mel. My point was that in all likelihood the asking party was making things more complex than they needed to be by introducing find when grep could do the job, but in some cases it would be more effective to to use find to fine tine the file list before going out to grep.

Mel grep does not choke in such a case, exec does. Works only in case all files are in the same directory, not when they are spread over subdirectories. Yaba My answer states how to handle the case of files spread over subdirectories.

Caleb's option is neater, fewer keystrokes. Mathew Mathew 1 1 silver badge 3 3 bronze badges. The problem with xargs is that it expects its input to be quoted in a peculiar way that find doesn't produce. Gilles You can get around that problem by using something like find. Obviously this is a horribly inefficient way to handle this example, but for some situations it's nice. For completeness we should also mention the -i option for case insensitivity with 'grep'.

Also there is -iname in find for case insensitivity. I use this often, but it will fail for very long lists of filenames, at which point find -exec becomes the winner. Ask and Learn Ask and Learn 1, 4 4 gold badges 18 18 silver badges 30 30 bronze badges. There is also pt platinum searcher, available at github. The Overflow Blog. The Overflow How many jobs can be done at home?

Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap.On Unix-like operating systems, exec is a builtin command of the Bash shell.

It allows you to execute a command that completely replaces the current process. The current shell process is destroyed, and entirely replaced by the command you specify. Traditionally, the only way to create a new process in Unix is to fork it.

exec pipe

The fork system call makes a copy of the forking program. The copy then uses exec to execute the child process in its memory space. The exec builtin command takes the following options and arguments :. When you exec a command, it replaces bash entirely — no new process is forked, no new PID is created, and all memory controlled by bash is destroyed and overwritten. This can be useful if, for instance, you want to give a user restricted access to a certain command. If the command exits because of an errorthe user will not be returned to the privileged shell that executed it.

For more information about redirection, see redirection in the bash shell. Replace the current bash shell with rbashthe restricted bash login shell. Because the original bash shell is destroyed, the user will not be returned to a privileged bash shell when rbash exits. Redirect all output to the file output. Redirections are a special case, and exec does not destroy the current shell process, but bash will no longer print output to the screen, writing it to the file instead.

This technique is much more useful in scripts — if the above command is executed in a script, all script output will be written to output. The above command is an example of explicitly opening a file descriptor.

See opening file descriptors in bash for more information. After running the above command, you can read a line of myinfile. Here, " -u 3 " tells read to get its data from file descriptor 3, which refers to myinfile. The contents are read, one line at a time, into the variable mydata. This would be useful if used as part of a while loop, for example. The above command opens out.Need support for your remote team? Check out our new promo! IT issues often require a personalized solution. Why EE?

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exec pipe

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Jitu asked. Medium Priority. Last Modified: I use Linux as my OS On commandline this works : cat myfile. I think the problem is with the usage of pipe. The output i get is only of cat myfile. What is the problem here? Start Free Trial. View Solution Only. Commented: The problem is that pipelining is not a part of the cat program. The Java simoply starts the cat program and pass parameters to it.Write Linux C program to create two processes P1 and P2.

P1 takes a string and passes it to P2. P2 concatenates the received string with another string without using string function and sends it back to P1 for printing. Inside Parent Process : We firstly close the reading end of first pipe fd1[0] then write the string though writing end of the pipe fd1[1].

Now parent will wait until child process is finished. After the child process, parent will close the writing end of second pipe fd2[1] and read the string through reading end of pipe fd2[0]. Inside Child Process : Child reads the first string sent by parent process by closing the writing end of pipe fd1[1] and after reading concatenate both string and passes the string to parent process via fd2 pipe and will exit.

This article is contributed by Kartik Ahuja.

Bash Redirections Using Exec

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It only takes a minute to sign up. So I'm trying to set up a systemd service in order to launch a set of files on a daily basis different types of journals from directories based off the date.

For example a todo list for today would be located in:. Now the easiest thing to do is to put it in a seperate directory, say today, and then have a bash script move it to the appropriate spot after the last modified time is no longer when it was created, or when the size of the file is larger than the template file.

But while that would be easier, I was wondering if it would be possible to write a script to return the directory of the file to be piped through the executed command in the service. Something along the lines of:. But you can invoke a shell explicitly, which would make it work. For example:. In effect, you don't really need a pipe here, you just need to determine the name of a directory and run atom with the proper redirect. Consider instead just implementing everything in a script and running it directly from the systemd unit.

The exec at the end of the shell script makes the shell replace itself with the atom program, so that systemd will end up running atom directly after setup. For this case it's not that important, so it could be omitted especially if you're interested in doing some kind of post-processing after the atom run. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Pipe output of script through Exec in systemd service? Ask Question.

Asked 1 year, 2 months ago. Active 1 year, 2 months ago. Viewed 3k times. Is this possible, or should I just stick to the already proposed solution? Joshua Ferguson Joshua Ferguson 41 1 1 silver badge 3 3 bronze badges.

What already proposed solution? How does the title match the question?


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Gardamuro Posted on07:58 - 17.10.2020

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