I am happily using constructs like the following; I have set -x to show fine distinctions.
Code:
$ exec 4> afile
+ exec
+ 4> afile
$ print -u4 This is the first line in afile
As you can see from the -x expansion, the shell performed the exec command and redirected file descriptor [4] to afile. And yes, the print to fd[4] works just fine.
Now what if I want to use a variable FD, as I would in C or Perl?
Code:
$ fd2=6
$ exec ${fd2}> another
+ exec 6
+ 1> another
ksh: exec: 6: not found
Not the difference: Instead of the blank exec command, it tried to execute a file named 6 and redirected stdout (fd[1]) to "another". This did create the file named "another" but it also closed the shell, as any erroneous exec would do.
So here's my question: Is there a way to open file descriptor via a variable?
By the way, back to fd[4]: Now that I have opened it, I can do this:
Code:
$ fd=4
$ print -u${fd} This is a second line in afile
and it expands to
Code:
+ print -u4 This is a second line in afile
as expected.
And, of course, whatever syntax can be used to open a FD via a variable needs to work to close it i.e. exec ${fd}>&-
I am trying to find a way to check the current status of a file. Such as some cron job processes are dependent on the completion of others. if a file is currently being accessed / modified or simply open state I will wait until it is done being processed before attempting the next process on that... (3 Replies)
I have a requirement to close all the file descriptors from 3 to 1024 for a particular application.
Right now, this is how I do it ..
for ( int i = 3 ; i <= 1024; ++i )
close(i);
The change I am looking at is, I want to do away with the number 1024 and replace it with a constant which... (4 Replies)
Im working on writing a small operating system. I am currently working on implementing dup, dup2, pipe, and close and I need to implement some type of file descriptor table in my PCB.
I was wondering if there is anyone who is familiar with linux/unix implementation of these tables who could... (6 Replies)
I am trying to right a function which uses a file descriptor to write to a log file. The problem is that the on the print statement the file descriptor is called bad. Now when I first open the file and print to it in the f_open function by passing the descriptor to f_print_log all works well,... (6 Replies)
Hello All,
Im opening a file desciptor in perl and sending data using print CMD "$xyz".
is there a limit to the length of the string that I can give to this CMD at a time. (3 Replies)
Hello,
How can i use file descriptor in a script to read 2 files at the same time and extract line 200 from file 1 and line 500 from file 2.
Thanks. (6 Replies)
I am trying to write a script which will only show me the file descriptor count for a process/pid. My script will return me the count only not the whole output. For example, I would like my script to return the output 23 this case, not the whole output.
Can anybody please help me how do I get... (11 Replies)
hello,
Someone can help me with redirectors?
I am writing this script in bash enviroment on Fedora:
exec 4<> /dev/tcp/10.10.11.30/5000 #open socket in input/output
strings<&4 >file.txt &
I send file descriptor 4 to string command to purge data stream from special char while come from... (3 Replies)
Discussion started by: rattoeur
3 Replies
LEARN ABOUT XFREE86
exec
exec(1) User Commands exec(1)NAME
exec, eval, source - shell built-in functions to execute other commands
SYNOPSIS
sh
exec [argument...]
eval [argument...]
csh
exec command
eval argument...
source [-h] name
ksh
*exec [arg...]
*eval [arg...]
DESCRIPTION
sh
The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may
appear and, if no other arguments are given, cause the shell input/output to be modified.
The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.
csh
exec executes command in place of the current shell, which terminates.
eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as
the result of command or variable substitution.
source reads commands from name. source commands may be nested, but if they are nested too deeply the shell may run out of file descrip-
tors. An error in a sourced file at any level terminates all nested source commands.
-h Place commands from the file name on the history list without executing them.
ksh
With the exec built-in, if arg is given, the command specified by the arguments is executed in place of this shell without creating a new
process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to mod-
ify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another program.
The arguments to eval are read as input to the shell and the resulting command(s) executed.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
EXIT STATUS
For ksh:
If command is not found, the exit status is 127. If command is found, but is not an executable utility, the exit status is 126. If a redi-
rection error occurs, the shell exits with a value in the range 1-125. Otherwise, exec returns a zero exit status.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), ksh(1), sh(1), attributes(5)SunOS 5.10 17 Jul 2002 exec(1)
12-28-2011
Variable File Descriptor
