Simulating the pipe "|" operator in C

[@evangelosspyromilios5994]

Students from 42 Salute you ! (Pipex project is pipe simulation in C)

[@SlowedOutOfExistence]

minishell for me hehe

[@ssergiu6559]

I almost clicked on the like button, pfew. Let's leave it at 42.

[@Lukssapgamer]

42 São Paulo here :P

[@sensoyyasin7215]

42 kocaeli is also here :)

[@evangelosspyromilios5994]

@@sensoyyasin7215 oh yes oh yes

[@ronoxdegrand]

These videos have helped me ALOT in my OS course at college

[@CARDSSerus]

I looked online for hours for material on a project I'm working on, finally found your channel, and found videos on basically everything I needed. You deserve way more attention

[@3IMAD69]

42 likes

[@fahidsarker4858]

you explained in 20 mins what my prof couldn't explain in 1 month. You earned a sub :-)

[@Grux]

OOOH man, this series was a huge helping hand in my shell project, so grateful for all the great vids of yours, thanks man!

[@juangil6227]

people: it's just another c video. me: bro, you literally saved my life

[@sharonmaldonado2114]

You have no idea the help you have provided. I was completely lost in my systems programming class during our final project, but this playlist you have made has helped me truly understand every little detail of pipes, forks, and exec functions. Thank you!

[@simon29o]

Thanks a lot ! I'm creating a shell (like TCSH) and your videos helps me a lot understand how to implement it

[@msd-007]

Thanks a lot. Your videos are damn excellent and help a lot in my projects. You explain everything and it's meaning , not like other sites that just give an example. Thanks from the depth of my heart. ❤ 💙 💜

[@zyghom]

imagine being Unix and Linux user for really long time, and using bash pipes on daily basis, only today I got the point about how the pipes work - thanks to your videos about the pipes - amazing!

[@zeuspolancosalgado3385]

I think my school should just outsource some of our professors and show us your videos

[@sony1979iq]

totally agree, many teachers dont have ability to deliver complex things in simple way, such as this channel

[@lukacsistvan6301]

Thanks man. I can learn more from your videos than from courses at university

[@harshildesai997]

Thank you so much for making this whole series . It helps me a lot in my academics

[@sony1979iq]

very nice explanation, one of my favorites channel in c learning

[@samgak_imbap862]

You are amazing at explaining this... Thank you for helping understanding how to do my assignments

[@aminabeid8136]

dude, you channel is a treasure, thank u so much!!!

[@aristuzabaru]

Amazing video! You make abstract concepts look so clear!

[@dsinemoi1mouton]

That's because it isn't abstract imo. Just not so commonly shared knowledge, and documentation barely tells anything about use cases. Amazing video indeed. Helps a ton.

[@anasajaanan7087]

I love your videos, you have the ability to make any concept very very easy ^_^

[@hectordoyle4718]

yo, i feel like you are my private tutor hahah thank you so much!

[@wenlinf1023]

thank you so much! couldn't understand how pipe works even after asking my professor. this video is very clear and helpful

[@ronitchinda6857]

Nice content : the way he explains it , is really awesome! Thanks , just keep making these kind of videos!

[@sukitd]

Thank you so much for your grateful work.

[@kawaranai6742]

Great lecture, helped me understand better than every written source I read. Request you to either number the lectures, or add them to a playlist (maybe there's one already?).

[@CodeVault]

There is one already: kzbin.info/www/bejne/mZbbaouoj6iIZ5Y Or on our website: code-vault.net/course/46qpfr4tkz:1603732431896/lesson/16non3fdoh:1603732431950

[@BigBobEdyS]

Thank you very much!! I’ve been searching for this info for 2 days

[@31GuitarKid]

This video helped a lot with a lab for my OS class! Thanks!

[@mouadse]

Great vid and excellent explanation. Thank you.

[@tsakboolhak5357]

Again thanks a lot with your videos! Your explanations are crystal clear! anyway i have a question : pipe function does open both fds , right? so if pipe() went well but another error occured, shouldnt we close the fds before returning error code?

[@CodeVault]

That is true... technically you should have a lot more error checking and closing of fds than I show on the video, but I didn't want to clutter the program with that, it would be difficult to follow. Also, a lot of the fds that we don't close get automatically closed by the operating system

[@tsakboolhak5357]

@@CodeVault allright, thanks for your time and your response!!

[@faiza.s6509]

Thank you so much, you are an amazing teacher!

[@ozanparlayan3471]

thank you very much for this beautiful video

[@olcaar]

Wow, you are an absolute life saver! thanks a lot for awesome and very well explained video. is there any way we can see all the codes you show in your videos? like at git or something?

[@CodeVault]

Thank you! You can check out all the source codes for any of the videos over on the website: code-vault.net/lesson/oxyoxbvnak:1603732432935

[@jackiehe8257]

Thank you so much for these videos! Great content and very clear step by step instruction!

[@juanguappo]

You are a legend, thank you for this videos!!!

[@npreme9193]

Great content, thanks so much

[@duanedsilva]

You can use system function to execute terminal commands with pipe operator.

[@CodeVault]

Oh, is there a function for doing this automatically? How would you do it?

[@filintodelgado]

I was thinking the same thing but It is always good to learn something new

[@NicosRap]

Great video! Thank you so much! So clear and consise!

[@Victor_Marius]

somebody should call a plumber...

[@benshapiro9731]

highkey saving my ass in my OS class, thank you good sir

[@TheMrBlueKoolaid]

Thank you !

[@carterchan1006]

lifesaver

[@poincareelcartografo5406]

On freeBSD it seems there is no need to close the main file descriptors: the program finish without doing so. However, I have closed them because I believe it is a good practice rule.

[@baselarw99]

Can you please make a diagram explaining the parent-child tree? cause in your second fork, you will have 4 processes, right? and we want only 3. (parent and 2 child)

[@CodeVault]

We only have 2 child processes here. Because the first fork() created one children which was replaced by the program we wanted to execute. So only the main process actually calls the second fork()

[@hackedyou116]

@CodeVault, why did u do 2 forks here? in the child process you can do ping and in parent you can do grep right?

[@paulinamystique]

I have the same question...

[@nik9911]

This helped me so much, thank you

[@MrTaandreo]

If you are from 42 i know that you are here :)

[@vishalbhatane1608]

thanks!

[@moamenalkatib2703]

thank you so much!

[@boutaina7925]

Thank you !!!

[@ansismaleckis1296]

If I understand correctly pipe() simply creates two temporary files to read and write. Can I achieve the same result by creating/opening/closing/deleting the temporary files myself? I understand that pipe() might be more convenient in some circumstances but is there any fundamental difference?

[@CodeVault]

A pipe does NOT create any temporary files. Everything is managed in the kernel's memory. While you could simulate a pipe's behavior by creating temporary files, it wouldn't be the same. More info here: superuser.com/questions/81679/does-pipe-have-to-write-temporary-file

[@James-l5s7k]

Are there any books that I should read to make me suck less with pipes? Linux programminmg by example i assume yes, but is there one from the perspective of a pure-c user in general?

[@CodeVault]

The C Programming language by the original creators of C would be a good start I think

[@HAPPYSPY]

You are a saint

[@maxmustermann9654]

Is it necessary to create two child processes? Why can't we just execute the first exec in the child process and the second one in the parent process? Something like this: main() { pid = fork(); if(pid == 0) { .... exec } ..... wait(NULL); exec; } That also works, but what is the big difference compared to creating two child processes?

[@CodeVault]

You can do this but there is one issue. The wait(NULL) placement. Since we have to wait for the child process to finish execution before executing the parent process. In some cases, this is fine, in others you would want the processes to run in parallel and, if you wanted that, you can't wait for the child process

[@maxmustermann9654]

​@@CodeVault Allright, thanks!

[@rezcov]

thank you for this video. Could you please clearify, why did you type name of command twice ("ping", "ping", ... "grep", "grep")? Cann't find manual regarding this cases.

[@CodeVault]

It's just the way you have to initialize argv. execlp("ping", "ping", "google.com"); Here, the first argument determines the program to be run and then the next two represent argv in the program we're running. It's a convention to pass the name of the program we are running as the first element of argv.

[@Viktor_Kardakov]

Спасибо большое! Вы очень хорошо всё объяснили.

[@abdullahgarra8477]

saved me with my operating systems hw!!

[@jingwu1425]

Could you create a video explaining popen()/pclose()?

[@OytunKuday]

thank you very much it helped our homework!!!!

[@minahoushmand8997]

why we dont't use just one fork and send data from child to parent and here you use two fork() and use two child to pipe() the data?

[@CodeVault]

Yes. You can use just one fork(). I thought that it was easier to understand if I used basically the same process for both processes that we try to execute

[@swastikdas4251]

sir in process 2 the exec system call is reading from arguments how can it read from stdin

[@CodeVault]

This video should explain how you can achieve that: code-vault.net/lesson/43zvcsz6o1:1603732432539

[@3finggaz]

Great ! thanks a lot 😀

[@gursahibsingh5177]

Too good!!!

[@vanessahaefeli5108]

Your videos are so usefull!!! I think the code on your website isn't finished. the last "close" aren't on it 😉

[@CodeVault]

Oh you're right! Should be fixed now. Thanks for pointing that out!

[@steptoevs996]

How can I read data such a variables from Pipes when using dup2() and write()/read() functions ?

[@CodeVault]

You can't make another program read/write specific variables through the pipe you dup2 on. You have to somehow do it beforehand (before the exec call) and maybe pass it as an argument

[@ahinoj]

Good video

[@SwenneHacks]

What vscode extension is he using that shows information/manual-info about functions on hover?

[@CodeVault]

It's just the C/C++ extension from Microsoft. It should work out of the box

[@jerrylin9018]

Hello, I'm trying to do output of Process A to input of process B and output of process B to input of A using what you did. so A->B->A->B..... Do you know what's wrong with my code? int AtoB[2],BtoA[2]; pipe(AtoB); pipe(BtoA); if(pipe(AtoB)==-1){return 1;} if(pipe(BtoA)==-1){return 1;} int pid,pid1; //process A if (pid==0){ dup2(AtoB[1], STDOUT_FILENO); close(AtoB[0]); close(AtoB[1]); dup2(BtoA[0], STDIN_FILENO); close(BtoA[0]); close(BtoA[1]); execv(Process A); //don't worry, I did write a cpp for B and used the right argv to call it; } else if (pid

[@CodeVault]

I suggest you go to discord.code-vault.net and ask there. It's probably much faster

[@dantearcuri3426]

How could you make this work with more than 1 pipe command? like ping | grep | wc for example.

[@CodeVault]

Same exact way but opening 2 pipes and calling dup2 4 times (one for stdout of ping, one for stdout of grep, one for stdin of grep and one for stdin for wc). Just makes sure you're closing the appropriate ends of each pipe in all processes.

[@mgking777]

@@CodeVault Hey , i am trying to make more than one pipe but i cannot reach the next one. For the middle proces between the two pipes i was trying to make dup2(fd[i]READ_END],STDIN_FILENO) and after that dup2(fd[i+1]WRITE_END],STDOUT_FILENO) and then execvp(...). What is a better way to do that?

[@mgking777]

nevermind i got the solution

[@karanarjun6245]

@@CodeVault we have forked 2 times... So total 4 process are created... So I am bit confused...so we don't need to close fd in those process?

[@lulu-wj8yt]

@@mgking777 Hi, i'm trying to do the same thing. where did you get the solution if you don't mind sharing the link ? thanks

[@chetanvenkatesh6051]

Amazing

[@hmdzed-bb9sf]

why we use two process when we can use just one? 🌹

[@CodeVault]

Yes, we can use just one extra child process. I'll leave it as a homework for you to try and implement :)

[@martinschulte3613]

This code doesn't look clean to me since you don't handle a possible failure auf execlp... - the program will hang if you substitute "ping" by "pong" (or delete /usr/bin/ping on your system)...

[@CodeVault]

That's true. Failures should be handled in production code

[@damonrobot906]

how would this be modified to support an arbitrary number of commands the user decides? eg. using n commands and n-1 pipes Thanks for your time Sergiu

[@CodeVault]

This video partially looks into this: code-vault.net/lesson/v5cml4fg0w:1610639843712 But instead of sending the number through the pipes you dup2 the STDIN and STDOUT of most processes and call exec at the end.

[@mgking777]

@@CodeVault When i exactly do this but, replace read and write with dup2 for STDIN and STDOUT and exec function , then there is no ouput on my console :( Im trying since hours but it wont work

[@maxcamilleri7004]

@@mgking777 did you ever get this to work?

[@mgking777]

​@@maxcamilleri7004 ​ Yes. You need to set the pipes differently. He is using for the first pipe fd[1]. But we have to do it differently. So if i = 0 we are at the beginning. So you need to use fd[i] because you wanna write in to the first pipe. Then in the "middle pipes" of the loop , when i > 0 you need to read from fd[i - 1] , because you wanna read from the "read end" of the previous pipe. Then write to the next pipe fd[i]. The middle part repeats untill we arrived the last pipe. Than we just need to read from fd[i - 1] and not write anything.

[@vladimir_khlghatyan]

Greate!

[@chocolatteu]

hello, how would the code change if I want n number of processes instead of creating the child processes one by one?

[@CodeVault]

There's this video on the topic: code-vault.net/lesson/v5cml4fg0w:1610639843712 Combine it with what you learned in the pipe simulation video and should work

[@emrederman880]

made my life easier thaank u a lot

[@manmmtk]

What if we hv so many pipe?

[@CodeVault]

It could get tricky. There's a video on dealing with any number of pipes: code-vault.net/course/46qpfr4tkz:1603732431896/lesson/v5cml4fg0w:1610639843712

[@ilyazlatkin4594]

Why it doesn't work with execv, but works with execlp?

[@CodeVault]

Probably because execv is missing the PATH variable. So you have to pass in the full path to your program (not just the executable's name)

[@yersonc8682]

can you simulate the ">" operator plis? :(

[@CodeVault]

I will look into it

[@matejdrazic7780]

How can you save the program output to a string?

[@CodeVault]

Just replace the stdout of the program with a pipe end. Then, on another process read from the pipe's read end

[@xiLike2Doitx]

@@CodeVault can I read on the parent process? Is that why it's not working for me so far?

[@naitside3410]

Ты очень хорошо объясняешь, только я ничего не понял так как говоришь не по русски. Я понял только что pipex это вертикальные полочки

[@CodeVault]

I might consider adding subtitles for different languages at some point. Thanks for the feedback!

[@naitside3410]

I rewrote the code, and I can’t go in, you can viklasty the code, be kind

[@CodeVault]

You can go to discord.code-vault.net and ask there for help

[@navguest1740]

which IDE is that, eclipse?

[@CodeVault]

No. It's Visual Studio Code

[@navguest1740]

@@CodeVault Thank you