UNIX - Response from command line
July 19, 2003 06:51 AM
How can get the response of OS into a string (like, after system("pwd"); )? (I know i can get the current dir without using pwd, it''s rather a general question on command line response).
1,088
July 19, 2003 10:54 AM
Setup a pipe and fork the process. In the child process close STDOUT (capitalized purposely) and duplicate (dup) the input end of the pipe (it''s kind of strange, but this causes the input end of the pipe to get STDOUT''s role). In the parent process, wait for the child to end ("waitpid") and read whatever you want out of the output end of the pipe.
4,872
July 19, 2003 11:03 AM
A simpler approach is to use popen(). You would do something like:
Basically, popen() forks a process for the specified command and attaches that process'' input (if mode is "w") or output (if the mode is "r") to the FILE stream.
FILE *fp = popen("mycommand my parameters","r");while (fgets(str,size,fp)){do something with str}fclose(fp); Basically, popen() forks a process for the specified command and attaches that process'' input (if mode is "w") or output (if the mode is "r") to the FILE stream.
124
July 19, 2003 03:25 PM
If you happen to be using Perl, then
will do the trick. It works in shell scripts, too.
$string = `pwd`; will do the trick. It works in shell scripts, too.
July 19, 2003 04:32 PM
Thanks 
Put when reading with pipe, I noticed a "while". So there''s more than 1? In an example, say these''re on the screen:
>Line1
>Line2
>Line3
>NextisCurrentInputLine_ThisIsLine4
>_
Now, if we call fread for the pipe, 1st it''ll read 4th, then 3rd, and so on, or it works differently?
Put when reading with pipe, I noticed a "while". So there''s more than 1? In an example, say these''re on the screen:
>Line1
>Line2
>Line3
>NextisCurrentInputLine_ThisIsLine4
>_
Now, if we call fread for the pipe, 1st it''ll read 4th, then 3rd, and so on, or it works differently?
4,872
July 19, 2003 10:22 PM
It works just like reading from a file. The first line read would be "Line 1".
739
July 20, 2003 09:40 AM
Moving by request of the original poster.
-fel
-fel
~ The opinions stated by this individual are the opinions of this individual and not the opinions of her company, any organization she might be part of, her parrot, or anyone else. ~
July 21, 2003 06:40 AM
not sure if this is related, but is it possible to map a file
descriptor or handle to a memory block? sort of like the opposite
of mmap in unix?
descriptor or handle to a memory block? sort of like the opposite
of mmap in unix?
4,872
July 22, 2003 11:48 AM
I''m not sure what you mean by "the opposite of mmap." mmap maps a file to a block of memory. Are you talking about mapping to a pre-allocated block? If so, I don''t know of a function to do that.
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