In case you have troubles working with the _execl() function and with the #include , try solely including and using the execl() function. This temporary solved my issues. Thank you for all the clear explanations!
unistd is only for unix based system and most probablly u cant use unistd in windows and also in windows with process u need to use _execl() but in unix u can use execl()
❤ A real Vault of Code!!! Your videos helped me a lot to understand not only how to use system calls, but also the principles of OS. I did bad in my undergraduate OS and computer network courses. Now I am taking graduate OS courses and reviewing the knowledge. Following your video, I am confident in being an OS/computer network engineer or researcher!
Great video. Thank you for your great explanation! Helped me a lot! On a side note, I believe this video is out of order in the Unix Processes in C playlist.
so since the execute function replaces the memory of the main program there is no way to return to the print statement at the bottom? Follow up question: Does that mean that a program can only have one execute function and its usually at the end, since everything after that is ignored?
Hi ! Thanks for this video ! I just don't understand why did you put in the second argument the same argument thant for the first in the execl function ? Can you explain me ? Thanks !
First "ping" is the program we want to execute. All the other arguments are sent to the ping program's arguments (to the argv and argc parameters in main basically). So, that second "ping" will be argv[0] inside the "ping" program
I have a question, how can you pass argv[i] in the execlp inside the string parameters? For example I want to call sed s/str1/str2/g but the str1 and str2 is argv[2] and argv[3] which is given from the user. So in fact I want to do execlp{"sed" , "sed" , "s/argv[2]/argv[3]/g", 0} ,but argv[2] , argv[3] supposed to be the input from the user in terminal.
Great Video! Thanks for the explanations about "v" "l" "e" that helps me a lot to remember this function. But i didn't understand this envp string and how to use it. Is there maybe an other video about that? So i watched the video about the main function parameters but it was not enough for me to work with envp. 🤔 Thank you so much for produce all this great videos!!!
I need to make a video on this envp variable. The main jist of it is, all the operating systems provide you with variables that you can set system-wide. These are being passed (usually by the OS) and accessed in the main function of each program.
@@CodeVault Would be nice =) i use it now with execve and extract the PATH= part first. But would be nice to know about the other informations in envp and why execve will have this variable.. idk. 😅
Hello Sir, thanks for the tutorial, that is very helpfull. but currently I am having a problem. When I execute the command "ls -R foldername > redirectionfile". It works in terminal, but in C It always yells the error "cannot access '>': No such file or directory". How can I solve this issue?
ls -R foldername > redirection Is actually a bash command since > is part of bash. You'll have to use sh with: sh -c "ls -R foldername > redirection" That third parameter will have to be one string that you pass to exec.
Microsoft Visual C compiler has these "_" prefixed functions, on other compilers you don't need them. These "exec" functions are originally from Unix systems (namely the unistd.h library) but got adopted by other platforms/compilers too.
With execvp you could just pass "date" as the first argument to the function (and the first element in the argv array). If you specifically need to use execv, you'll have to pass in the path to the "date" executable instead. You can find the path by running this command on your computer: whereis date You can do this for any command you don't know the path of
how can we use the _exec if you are going to send the project to another person ,because the adress or the path will change so how can we deal with it ?
You can use execlp (or any exec function that ends in p). This one uses the PATH variable and you only need to give it the executable's name and not the whole path
Family of exec function is not working in visual studio on Windows connected to WSL UBUNTU Linux . Fork() is working fine but exec family is not working neither it is showing any error it's just ignored in program 😦 Please help is, there anything with directory @CodeVault
Let's say there is a date command that prints the date on the screen. I want to call it, but then I want my C code to continue. How to do that? Just call a process, wait for it, and when it's finished, continue the C code. I don't want the called process to take my program over. Thanks.
You can use fork() (or CreateProcess()) to spawn another process, then, in the spawned process call exec while in the parent process wait for the child process to finish executing. I might make a video on this.
I writing a linux shell and have the task to execute programs with a child process but i dont really unterstand if their is a way that the parent (main process) dont wait for the child, without the waitpid i have the weird bug that my child use the same while loop as the main. I thought that if i call execvp, that the child only execute this.
@@CodeVault So my Problem is that i have to wait for the child process to finish, if the parent dont wait for the child with waitpid, its run also the main code and print printf("Give Input: ");. How can i stop that ? Does i have to wait for the process to finish ? I thought if i execute execvp() the child process never comes pack to the main function. Also if i dont use waitpid, it doesnt print "something", but i know why
So basically you always have to wait for a child process regardless if you used execvp on it or not (otherwise there are certain resources that are almost never released). BUT, you don't have to wait right after calling fork, you can call waitpid anywhere in the parent process, for example, right before your return 0 in the main function. That way your while loop can continue.
If I want to exec some program that the user input, like, the user puts " firefox ", how can I exec that program, because the path can change of pc for pc...
There's execp/execlp/execvp for that which makes use of the PATH environment variable. If the user set it correctly, you shouldn't need to mess with paths
@@CodeVault import sys from subprocess import run def start(navegador, site): run([navegador, site]) def main(): from threading import Thread from time import sleep navegador = input("navegador: ") site = input("site: ") tempo = input("tempo: ") thread = Thread(target=start, args=(navegador, site)) thread.start() sleep(60*tempo) run(["pkill", navegador]) Im learning C now, and I was trying to make this same code of python, but in C
Hey there I have a question. Say I have my own program "myprogram.exe" and I want to call "myprogram" instead of ping(which you called usign execl() function). I have done this I can call "myprogram" and it runs as expected. Now the part I don't get is how do I make my "myprogram" to get those arguments passed through execl() and act accordingly ? Like how does this argument passing work ? Let me give you an example, I want to print '24' on screen so I write my "myprogram.exe" to print '24' only on a certain condition. And I want that condition be evaluated from the argument that is passed by execl() when it called. Just like ping accepted the argument and acted accordingly, how can I make my "myprogram" to act according to arguments passed from execl()? Englighten me if you have any idea about it.
Dude your videos are life saving! I'm beginning to actually understand my computer systems class because of them. Thank you so much!
Thank you, sir, for great explanation and examples. Good job!
I've really been enjoying your content. Thanks for all your great work and well constructed presentations.
Thank you very much for this video. Excellent explanation and demo. Saved me many hours or reading and messing about.
Just worked with Shell project following your tutorials. Thanks
I just finished my Shell Project yesterday ! you are reading my mind ...
Bro is there a way to thank you financially for your help ? You saved my semester, I would like to thank you for that
He's Saving so many semesters ahahahahahha
@@xxjblexx Every year😭
You are saving my semester thank you
In case you have troubles working with the _execl() function and with the #include , try solely including and using the execl() function.
This temporary solved my issues.
Thank you for all the clear explanations!
unistd is only for unix based system and most probablly u cant use unistd in windows and also in windows with process u need to use _execl() but in unix u can use execl()
You are the hero of CS students the world over! Thanks so much
This is the best exec tutorial! :D
❤ A real Vault of Code!!! Your videos helped me a lot to understand not only how to use system calls, but also the principles of OS. I did bad in my undergraduate OS and computer network courses. Now I am taking graduate OS courses and reviewing the knowledge. Following your video, I am confident in being an OS/computer network engineer or researcher!
In my opinion, you are much better than uni's doctors 🌚.
THANK YOU SO MUCH FOR YOUR EFFORT!!
You can use a buffer to write OUTPUT and ERROROUTPUT to a Buffer string or byte Buffer and print it out after execution.
You did it, thanks bud!
Amazing video for exec and os in general.
Thank you for the great explanation!
AWESOME. Very clear explanation!
Thanks a lot, much clearer than my professor's instruction
Great video, you were ultra helpful. Thank you very much
Thank you so much for this video.. I understood everything.. thanks alot.. . loved it..
very good explanation!Thank you!
Great video. Thank you for your great explanation! Helped me a lot!
On a side note, I believe this video is out of order in the Unix Processes in C playlist.
It was a standalone video but I thought it was important enough to add it to the playlist. Were some concepts difficult to understand in this video?
great video, very clear explanation
great video, clearly explanation!
very helpful, thank You!
one of the best channels
Nice, thanks bro!
Thank you for your videos
so since the execute function replaces the memory of the main program there is no way to return to the print statement at the bottom? Follow up question: Does that mean that a program can only have one execute function and its usually at the end, since everything after that is ignored?
Yes, unless you're creating a child process to execute that command on. Follow up lesson: code-vault.net/lesson/as15alvu0a:1603732432433
wow.. very informative...
You are a Legend!
Please do videos on creating libraries and linking it to a code and building it on linux
Hi ! Thanks for this video ! I just don't understand why did you put in the second argument the same argument thant for the first in the execl function ? Can you explain me ? Thanks !
First "ping" is the program we want to execute. All the other arguments are sent to the ping program's arguments (to the argv and argc parameters in main basically). So, that second "ping" will be argv[0] inside the "ping" program
nice explanation
I have a question, how can you pass argv[i] in the execlp inside the string parameters? For example I want to call sed s/str1/str2/g but the str1 and str2 is argv[2] and argv[3] which is given from the user. So in fact I want to do execlp{"sed" , "sed" , "s/argv[2]/argv[3]/g", 0} ,but argv[2] , argv[3] supposed to be the input from the user in terminal.
You can simply use a function that formats your string like:
sprintf(res, "s/%s/%s/g", argv[2], argv[3]);
And then just pass that res string to execlp
@@CodeVault oh , Thank you so much!
Question, so if I were to fork this into a new process, would still close everything?
I'm not sure what you mean, can explain your question a bit better?
Awesome videos man but damn if I am wearing headphones I think your keystrokes are giving some bass lol
Yeah, I think I fixed the issue in later videos, sorry about that
you probably get alot of comments like this but this video was indeed life saving :D
thanks sir
Great Video! Thanks for the explanations about "v" "l" "e" that helps me a lot to remember this function. But i didn't understand this envp string and how to use it. Is there maybe an other video about that? So i watched the video about the main function parameters but it was not enough for me to work with envp. 🤔 Thank you so much for produce all this great videos!!!
I need to make a video on this envp variable. The main jist of it is, all the operating systems provide you with variables that you can set system-wide. These are being passed (usually by the OS) and accessed in the main function of each program.
@@CodeVault Would be nice =) i use it now with execve and extract the PATH= part first. But would be nice to know about the other informations in envp and why execve will have this variable.. idk. 😅
Hello Sir, thanks for the tutorial, that is very helpfull. but currently I am having a problem. When I execute the command "ls -R foldername > redirectionfile". It works in terminal, but in C It always yells the error "cannot access '>': No such file or directory". How can I solve this issue?
ls -R foldername > redirection
Is actually a bash command since > is part of bash. You'll have to use sh with:
sh -c "ls -R foldername > redirection"
That third parameter will have to be one string that you pass to exec.
hey! thanks!!!!!
What if i want to execute a script shell throughout a c program, i got the path, but which function to use and what would the arguments be? Thank youu
You can actually use sh like so to execute a shell script:
execlp("sh", "-c", "ls -la", NULL);
@@CodeVault you probably have no idea but you saved me, thaaank youuuu!!
Is the _ necessary? My IDE seems to work without the underscore.
Microsoft Visual C compiler has these "_" prefixed functions, on other compilers you don't need them. These "exec" functions are originally from Unix systems (namely the unistd.h library) but got adopted by other platforms/compilers too.
What about using the perror or strerror functions instead of using directly errno ?
You can use that as well! I don't like perror because there's no format string so I usually use fprintf(stderr, ...) instead
How can I use the execv function in order to execute system commands, like "date"?
With execvp you could just pass "date" as the first argument to the function (and the first element in the argv array). If you specifically need to use execv, you'll have to pass in the path to the "date" executable instead. You can find the path by running this command on your computer:
whereis date
You can do this for any command you don't know the path of
Good👌👌
do you have video about heap data structure?
No, I'm sorry, we don't have much about data structures yet
Good and useful
how can we use the _exec if you are going to send the project to another person ,because the adress or the path will change so how can we deal with it ?
You can use execlp (or any exec function that ends in p). This one uses the PATH variable and you only need to give it the executable's name and not the whole path
Family of exec function is not working in visual studio on Windows connected to WSL UBUNTU Linux . Fork() is working fine but exec family is not working neither it is showing any error it's just ignored in program 😦
Please help is, there anything with directory @CodeVault
Haven't tried that yet so I'm not sure how it works on WSL. How do you call fork?
@@CodeVault instead of local machine select wsl in VS'configuration and then it works
Btw I'm using createprocess() now
🤩🤩🤩🤩🤩
Let's say there is a date command that prints the date on the screen. I want to call it, but then I want my C code to continue. How to do that? Just call a process, wait for it, and when it's finished, continue the C code. I don't want the called process to take my program over. Thanks.
You can use fork() (or CreateProcess()) to spawn another process, then, in the spawned process call exec while in the parent process wait for the child process to finish executing.
I might make a video on this.
@@CodeVault would be great!
I writing a linux shell and have the task to execute programs with a child process but i dont really unterstand if their is a way that the parent (main process) dont wait for the child, without the waitpid i have the weird bug that my child use the same while loop as the main. I thought that if i call execvp, that the child only execute this.
I'm not sure I understand your issue. Can you send in the code?
@@CodeVault
So my Problem is that i have to wait for the child process to finish, if the parent dont wait for the child with waitpid, its run also the main code and print printf("Give Input:
");. How can i stop that ? Does i have to wait for the process to finish ?
I thought if i execute execvp() the child process never comes pack to the main function. Also if i dont use waitpid, it doesnt print "something", but i know why
So basically you always have to wait for a child process regardless if you used execvp on it or not (otherwise there are certain resources that are almost never released). BUT, you don't have to wait right after calling fork, you can call waitpid anywhere in the parent process, for example, right before your return 0 in the main function. That way your while loop can continue.
@@CodeVault ahhh thank you very mutch
How would I use it to launch programe from another if it step out the code in other word my main program gonna end itself ?
You can use fork() in this case. Take a look at this video: code-vault.net/course/46qpfr4tkz:1603732431896/lesson/as15alvu0a:1603732432433
@@CodeVault fork only works in Linux envr
@@CodeVault I’ve found another solution using shell exec in windows envr
If I want to exec some program that the user input, like, the user puts " firefox ", how can I exec that program, because the path can change of pc for pc...
There's execp/execlp/execvp for that which makes use of the PATH environment variable. If the user set it correctly, you shouldn't need to mess with paths
@@CodeVault like, the user set manually the dir of the program alright?
@@CodeVault import sys
from subprocess import run
def start(navegador, site):
run([navegador, site])
def main():
from threading import Thread
from time import sleep
navegador = input("navegador: ")
site = input("site: ")
tempo = input("tempo: ")
thread = Thread(target=start, args=(navegador, site))
thread.start()
sleep(60*tempo)
run(["pkill", navegador])
Im learning C now, and I was trying to make this same code of python, but in C
Yes
@@CodeVault thanks for your attention man, Im waiting for new videos :) bye
This video is in the wrong order in the playlist can you fix it pls ?
I fixed it. Thanks for telling me
What if we want to execute rest of the program seamlessly?
Already addressed .. Thanks
Can we just use system ()? Why not?
Yes, you can too
Noice
anything I know or did
Hey there I have a question. Say I have my own program "myprogram.exe" and I want to call "myprogram" instead of ping(which you called usign execl() function). I have done this I can call "myprogram" and it runs as expected. Now the part I don't get is how do I make my "myprogram" to get those arguments passed through execl() and act accordingly ? Like how does this argument passing work ?
Let me give you an example, I want to print '24' on screen so I write my "myprogram.exe" to print '24' only on a certain condition. And I want that condition be evaluated from the argument that is passed by execl() when it called. Just like ping accepted the argument and acted accordingly, how can I make my "myprogram" to act according to arguments passed from execl()?
Englighten me if you have any idea about it.
That's exactly what argc and argv are for. You can learn more about them in this video: code-vault.net/lesson/dbijqbwu2a:1603733526118