I want to change directory in unix using code in a C file.I tried this:
char command[50];
strcpy( command, "cd newdirectory/" );
system(command);
but it didn't work.Other commands using "system" work.
To change directory try to use chdir. A related question is How to change the working directory in C?. About using system see Why can't we change directories through system() system call in Linux? and Changing the current directory in Linux using C++.
your command would work, but only within the system() call. e.g.: if you do system("cd newdirectory && rm foo");, rm foo will happen in newdirectory.
That's because the system() call does an fork() where you change the environment, but when it gets back to your calling program, you get back to your original environment.
To change the directory of your current process, you have to follow user1929959's answer: i.e. usinc the chdir() system call.
Related
i have a trouble with :
system("cd mypath");
when i try this in C programming language terminal doesn't do anything.
i need help.
The system function creates a whole new process, separate from the one calling the function.
Each process have its own current working directory associated with it, and this working directory is specific to that process only. Changing the working directory of one process will not change it for another process.
If you want to change the working directory of your own process use operating-system specific functions to to it. Like chdir on Linux (and other POSIX system like macOS), or SetCurrentDirectory in Windows.
Note that if you change directory in your own process, the directory of the shell or console that invoked your program will not be changed, as it's also a separate process from yours.
look just do
chdir("path");
or
system("chdir PATH"); //linux
I am using chdir() to change directory to the value passed as an argument to this function.
I understand that when I run my C program using gcc myCd.c and ./a.out .. this changes the directory to the parent directory "within" the C program (i.e. a child process is spawned for the a.out process, and the change of directory happens within that child process).
What I want to do is, change the directory at the terminal using this C program. I tried writing a shell script for the same, and then sourcing it, and running, that works, but I wanted to achieve this using C.
What you are attempting to do can't be done. The current working directory is a per-process attribute.
If you run a program which changes its cwd, it does not affect any other processes, except for any children it might create after the chdir().
The correct way to change the terminal's working directory is to use the cd command which the shell executes on your behalf and remains within the same process. That is, cd is one of several commands that the shell does not fork(); this makes the cd command work as expected.
sourceing a shell file makes it run within the shell's process. However, if you were to run the script without source, you'd find there was the exact same problem as with a C program: the shell forks to create a process for the script to run, it runs and then exits, and then the shell continues, but without its cwd changed.
this is the way to change the current working directory in C
this needs the unistd.h header file to be included
if( 0 != chdir( "pathToNewDirectory" ) )
{ // then chdir failed
perror( "chdir failed" );
// handle error
}
I'm just getting started with C.
What I want to do is issue Unix commands from C, especially with system().But if I have code like this, it can only access files in the same directory.
system("./Test");
But I want to use that code in any directory. Is it possible?
system("/any/other/folder/Test");
calling command via system is like calling command via command line interface so even the path of your command is ../../any/other/folder/Test, you call it with
system("../../any/other/folder/Test");
Just pass an absolute path as parameter
system("/your/folder/Test");
system() forwards its string parameter to the native command line handler - e.g. /bin/sh on Unix or cmd.exe on Windows. You can use whatever command or path those whould take. Of course, such code is not portable.
I know that cd is a shell built-in ,and I can run it by using system().
But is that possible to run the cd command by the exec() family, like execvp()?
Edit: And I just noticed that system("cd") is also meaningless。Thanks for the help of everyone.
exec loads an executable file and replaces the current program image with it. As you rightly noted, cd is not an executable file, but rather a shell builtin. So the executable that you want to run is the shell itself. This is of course what system() does for you, but if you want to be explicit about it, you can use exec:
execl("/bin/sh", "-c", "cd", (const char *)0);
Since this replaces your current process image, you should do this after fork()ing off a new process.
However, this entire procedure has absolutely no effect. If you want to change the directory in your current process, use chdir().
You're better off using int chdir(const char *path); found in unistd.h.
No it is not, and it would be of no use. chdir (the function that changes a process's current directory) only affects the process that calls it (and its children). It does not affect its parent in particular.
So execing cd has no point, since the process would exit immediately after having changed directories.
(You could exec something like bash -c cd /tmp if you really want to, but as I said, this is fruitless.)
While, as already stated system("cd xxx") wouldn't change your application current directory, it is not completely useless.
You can still use system exit status to know if changing your current directory to the one stated would succeed or not.
Similarly, if you like complex solutions, you could also do the same with fork/exec, either with exec'ing /bin/sh -c cd xxx or simply /bin/cd xxx with OSes that provide an independent cd executable.
I would however recommend this non overkill faster equivalent access("xxx", X_OK|R_OK)
Note: All POSIX compliant OSes must provide an independent cd executable. This is at least the case with Solaris, AIX, HP-UX and Mac OS/X.
When a fork is done the environment variable CWD(current working directory) is inherited by the child from the parent.If fork and exec is done as usual then the child calls chdir() which simply changes the directory to the new directory and exits but this does not affect the parent.Hence, the new environment is lost..
I have to change working directory from my C program. For this I have used the following command:
execl("/bin/cd","cd","..",(char*)0);
but this command is not changing the directory?
Is anything wrong in this command or is there any other way to change working directory from C program?
To change the current directory you should use chdir:
int chdir(const char *path);
On success it returns 0.
You can't use execl for several reasons:
cd is typically a shell builtin command;
on most systems /bin/cd does not exists; on the very very few systems that have it, it changes the current directory and then spawns a child shell process;
the current directory is a process' property: if you change the current directory using /bin/cd, you'd lose the directory change as soon as the process terminates;
if you use a function from the exec family, the current process image is replaced with a new process image - you could use system, but wouldn't fix the previous 3 problems.
What you are doing won't work because the exec family of calls will actually replace your current program in the current process. In other words, you will have been terminated so that, when cd is finished, your parent process will once again take over.
If you want to change the working directory for the current process, use chdir. If you want to change it on exit, you're out of luck because your program itself is running in a separate process from the parent that started it.
So, unless you have some form of communication with the parent, that's not going to work.
You need to use the chdir system call to change the working directory of the calling process.