Hello, I'm currently implementing the && function in a shell using C. For example, if we input cmd1 && cmd2, then cmd2 executes only when cmd1 exits successfully. I'm thinking about:
Code:
int main() {
int i;
char **args;
while(1) {
printf("yongfeng's shell:~$ ");
args = get_line();
if (strcmp(args[0], "exit") == 0) exit(0); /* if it's built-in command exit, exit the shell */
if('&&') parse_out_two_commands: cmd1, cmd2;
if (execute(cmd1) != -1) /* if cmd1 successfully executed */
execute(cmd2); /* then execute the second cmd */
}
}
int execute(char **args){
int pid;
int status; /* location to store the termination status of the terminated process */
char **cmd; /* pure command without special charactors */
if(pid=fork() < 0){ //fork a child process, if pid<0, fork fails
perror("Error: forking failed");
return -1;
}
/* child */
else if(pid==0){ /* child process, in which command is going to be executed */
cmd = parse_out(args);
/* codes handleing I/O redirection */
if(execvp(*cmd, cmd) < 0){ /* execute command */
perror("execution error");
return -1;
}
return 0;
}
/* parent */
else{ /* parent process is going to wait for child or not, depends on whether there's '&' at the end of the command */
if(strcmp(args[sizeof(args)],'&') == 0){
/* handle signals */
}
else if (pid = waitpid(pid, &status, 0) == -1) perror("wait error");
}
}
So I'm using another function int execute(char ** args) to do the actual work. Its return type is int because I wan to know whether the command exits successfully. But I'm not sure here whether the parent process can get the return value from the child since they're two different processes.
Or should I decide whether to execute the second command in the child process, by forking another process to run it? Thanks a lot.
Hello all,
Can someone explain to me the advantage between using subshell over a function call in scripts? To me these are the same. Am I wrong to think this? (4 Replies)
Hi,
If this is the array that is being returned to me:
How would I get the values for each of the 3 records?
This works for 1 Record:
foreach $item (@results)
{
($id, $id2, $name, $date, $email) = split(/\|/, $item, 5);
print "$name<br>";
} (2 Replies)
I am going to take up a position in Data & Network Security.
I would need to write network shell scripts doing the following task:
Going to around 2000 servers and findout which groups has access to each servers and which ids are there in each group that has access.
I need to implement... (1 Reply)
Hello to all,
I am looking for a way to display only the names of function (calls & definition) of a C++ source code.There is already a post related to this, but the script is to find the functions using a specific variable, and the replies are not that convincing since they cannot be used for... (2 Replies)
Hi, I hope the title does not scare people to look into this thread but it describes roughly what I'm trying to do. I need a solution in PHP.
I'm a programming beginner, so it might be that the approach to solve this, might be easier to solve with an other approach of someone else, so if you... (0 Replies)
Hello All
I have a xml file with many sets of records
like this
<mytag>mydata</mytag>
<tag2>data&</tag2>
also same file can be like this
<mytag>mydata</mytag>
<tag2>data&</tag2>
<tag3>data2&data3</tag3>
Now i can grep & and replace with & for whole file but it will replace all... (4 Replies)
Hi, I have text file abc.txt. In this file, I have the following data.
Input:
Mr Smith & Mrs Smith
Mr Smith &apos Mrs Smith
Mr Smith & Mrs Smith
Mr Smith& Mrs Smith
Mr Smith &Mrs Smith
Output:
Mr Smith & Mrs Smith
Mr Smith &apos Mrs Smith
Mr Smith & Mrs Smith
Mr Smith&... (4 Replies)
How to use MAN to find information about read() and write() function ?
The command "man read" show some rubbish, for example "man open" show great information about function I need. (2 Replies)
Hi All,
Do you have any sample script,
- auto get file from SFTP remote server and delete file in remove server after downloaded.
- only download specify filename
- auto upload file from local to SFTP remote server and delete local folder file after uploaded
- only upload specify filename
... (3 Replies)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
2. Relevant commands, code, scripts, algorithms:
#! /bin/ksh
v="ORG_ID"
... (2 Replies)
Discussion started by: sujitdas2104
2 Replies
LEARN ABOUT OSX
ipc::open2
IPC::Open2(3pm) Perl Programmers Reference Guide IPC::Open2(3pm)NAME
IPC::Open2 - open a process for both reading and writing using open2()
SYNOPSIS
use IPC::Open2;
$pid = open2(*CHLD_OUT, *CHLD_IN, 'some cmd and args');
# or without using the shell
$pid = open2(*CHLD_OUT, *CHLD_IN, 'some', 'cmd', 'and', 'args');
# or with handle autovivification
my($chld_out, $chld_in);
$pid = open2($chld_out, $chld_in, 'some cmd and args');
# or without using the shell
$pid = open2($chld_out, $chld_in, 'some', 'cmd', 'and', 'args');
waitpid( $pid, 0 );
my $child_exit_status = $? >> 8;
DESCRIPTION
The open2() function runs the given $cmd and connects $chld_out for reading and $chld_in for writing. It's what you think should work when
you try
$pid = open(HANDLE, "|cmd args|");
The write filehandle will have autoflush turned on.
If $chld_out is a string (that is, a bareword filehandle rather than a glob or a reference) and it begins with ">&", then the child will
send output directly to that file handle. If $chld_in is a string that begins with "<&", then $chld_in will be closed in the parent, and
the child will read from it directly. In both cases, there will be a dup(2) instead of a pipe(2) made.
If either reader or writer is the null string, this will be replaced by an autogenerated filehandle. If so, you must pass a valid lvalue
in the parameter slot so it can be overwritten in the caller, or an exception will be raised.
open2() returns the process ID of the child process. It doesn't return on failure: it just raises an exception matching "/^open2:/".
However, "exec" failures in the child are not detected. You'll have to trap SIGPIPE yourself.
open2() does not wait for and reap the child process after it exits. Except for short programs where it's acceptable to let the operating
system take care of this, you need to do this yourself. This is normally as simple as calling "waitpid $pid, 0" when you're done with the
process. Failing to do this can result in an accumulation of defunct or "zombie" processes. See "waitpid" in perlfunc for more
information.
This whole affair is quite dangerous, as you may block forever. It assumes it's going to talk to something like bc, both writing to it and
reading from it. This is presumably safe because you "know" that commands like bc will read a line at a time and output a line at a time.
Programs like sort that read their entire input stream first, however, are quite apt to cause deadlock.
The big problem with this approach is that if you don't have control over source code being run in the child process, you can't control
what it does with pipe buffering. Thus you can't just open a pipe to "cat -v" and continually read and write a line from it.
The IO::Pty and Expect modules from CPAN can help with this, as they provide a real tty (well, a pseudo-tty, actually), which gets you back
to line buffering in the invoked command again.
WARNING
The order of arguments differs from that of open3().
SEE ALSO
See IPC::Open3 for an alternative that handles STDERR as well. This function is really just a wrapper around open3().
perl v5.16.2 2012-10-11 IPC::Open2(3pm)