With fconfigure you can get and set channel options. -buffering specifies the type of buffering, and by default it is line for stdin.
Is there a way to check if the buffer at stdin is empty or not?
Please see this question: How to check if stdin is pending in TCL?
Obviously you could set the channel mode to non-blocking and read from it. If the read returns 0 length then nothing was available. However, I suspect you mean to test for data present but not a complete line given your mentioning of the line buffering there. The fblocked command tests a channel for this. See fblocked(1) for the details but for a line buffered channel this lets you know that an incomplete line is present.
Another useful command when reading stdin, if you are reading interactive script commands is to use the info complete command. With this you can just accumulate lines until info complete returns true then evaluate the whole buffer in one.
You can check Tcl's input buffer with chan pending input stdin (requires at least Tcl 8.5). This does not indicate whether the OS has anything in its buffers though; those are checked by trying to read the data (gets or read) or by using a script that triggers off of a readable fileevent, when at least one byte is present. (Well, strictly what is actually promised is that an attempt to read a single byte won't block, but it could be because of an error condition which causes immediate failure. That's the semantics of how OS-level file descriptor readiness works.)
The -buffering option only affects output channels; it's useless on stdin (or any other read-only channel) and has no effect at all. Really. (It is, however, too much trouble to remove.)
I know this is an old question but it sparked some research on my end and I found a function called fileevent which calls an event handler when the stream, i.e. stdin, has something in it that can be read. It may be helpful.
Source: http://wiki.tcl.tk/880
Related
I am using C in Objective C and I want to capture stdout to UIView from Console.
Here is the line I'm talking about:
print(stdout, v=toplevel_eval(v));
Other than you are writing in C I have no idea how much you know about C, "Unix" and Cocoa I/O - so some of this you may already know.
Here is one possible solution, it looks more complicated than it is.
Reading:
You need to understand the system calls pipe, dup2 and read.
You need to understand the GCD function dispatch_async and how to obtain a GCD queue.
pipe and dup2 are often used in conjunction with fork and exec to launch a process and write/read to/from that process standard input/output. What you will be doing uses some of the same basic ideas so looking up examples of this common pattern will help you understand how these calls work. Here are some notes from a University: Pipe, Fork, Exec and Related Topics.
Outline:
Using dispatch_async schedule a block to handle the reading and writing of the data. The block will:
Use pipe To create a pipe and dup2 To connect stdout - file descriptor 1 - it.
Enter a loop which uses read to obtain the available data from the pipe. Data read will be in a byte array.
Within the loop convert the read bytes into an NSString
Within the loop append that string to your view - you must do this on the main thread as it involves the UI, and you can do that using another dispatch_async specifying the main queue.
That is it. Your block will now execute concurrently in the background reading whatever your C code writes to the standard output and adding it to your view.
If you get stuck you can ask a new question showing the code you have written and describing what doesn't work.
HTH
I use the following to save screen output to a file
writefile("file.txt"),
tex(expression),
closefile()
The above sends the output of the tex() to the file automatically. which is all and well and what I want. (side-point: It also sends an annoying NIL line each time to the file, which I had to parse put later).
Now, when running the above code again, the file is appended to, which is not what I want. I want to either overwrite the file each time, or if there is a way to delete the file, so I can call delete on it before.
I looked at help and not able to find a command to delete a file, and I also see no option to tell writefile() to overwrite the file?
Is there an option or way around this? I am on windows 7, Maxima version: 5.36.1
Lisp: SBCL 1.2.7
I guess you are trying to capture the output of tex into a file. If so, here are a couple of other ways to do it:
tex (expr, destination);
where destination is either a file name (which is appended) or a stream, as created by opena or openw and closed by close. By the way, destination could be false, in which case tex returns a string.
with_stdout (destination, tex (expr));
where again destination is either a file name (which is appended or clobbered, as determined by the global flag file_output_append) or a stream.
with_stdout could be useful if you want to mix in some output not generated by tex, e.g., print("% some commentary");.
I'm using flex & bison to parse a custom language and I'm in the situation described here: http://www.gnu.org/software/bison/manual/html_node/How-Can-I-Reset-the-Parser.html.
To be more precise
I invoke yyparse several times, and on correct input it works
properly; but when a parse error is found, all the other calls fail
too. How can I reset the error flag of yyparse?
My parser and scanner run inside a separate thread, but there is only one thread working with the input file. In my understanding I don't need to write a reentrant scanner since there is only one thread working with the input file. In that page the problem is clearly explained but the solution is not clear to me.
It says:
Therefore, whenever you change yyin, you must tell the Lex-generated
scanner to discard its current buffer and switch to the new one. This
depends upon your implementation of Lex; see its documentation for
more. For Flex, it suffices to call ‘YY_FLUSH_BUFFER’ after each
change to yyin. If your Flex-generated scanner needs to read from
several input streams to handle features like include files, you might
consider using Flex functions like ‘yy_switch_to_buffer’ that
manipulate multiple input buffers
My parser thread calls yyparse in order to build my AST. What is not clear to me is when and where I have to call yy_flush_buffer to fix the problem. In my understanding the scanner code (generated by Flex) is called by the parser code (generated by Bison). The Bison generated code is generated by the grammar. As a result the parser code is not under my direct control. This means I cannot include the call to yy_flush_buffer into the parser code since it would be overwritten every time I generate the parser code by the grammar. It means that I should put the yy_flush_buffer in the grammr file somewhere. But where?
I fixed the problem by doing:
...
FILE *f = fopen(_filename, "r");
yyrestart(f);
yyparse();
...
I leave the question since it could be useful for other people.
I want to read php://stderr. How can do it?
Do php://stderr and STDERR write to the same file? Because after writing to php://stderr I tried reading STDERR using stream_get_contents but I did not get any data?
Also while writing to php://stderr using file_put_contents do we need to use APPEND flag so that the data is not overwritten.
It is recommended that you simply use the constants STDIN, STDOUT and STDERR instead of manually opening streams using these wrappers.
http://www.php.net/manual/en/wrappers.php.php
You can't read from php://stderr.
Building on the answer of #user647772:
It is recommended that you simply use the constants STDIN, STDOUT and STDERR instead of manually opening streams using these wrappers.
...
php://stdin is read-only, whereas php://stdout and
php://stderr are write-only.
Source: http://www.php.net/manual/en/wrappers.php.php
Also since php://stderr essentially points to a stream using the APPEND is not needed because there is nothing to overwrite (since it's not a file). Streams can not be overwritten by nature. You just put something in or get something out of a stream.
Is it possible to abend your job intentionally through COBOL program.
suppose I have an Input file having Header,Detail and Trailer records. I will write a COBOL pgm which reads this file.If no Detail records are found in this file then I want to abend my job by giving some Abend Message and some Abend Code.Is it Possible?
Do you want to ABEND your program or just set a RETURN-CODE?
I suspect setting a RETURN-CODE, writing a message
and then terminating the program via a STOP RUN or GOBACK is all that
you really want to do. Causing an actual ABEND may not be necessary.
In an IBM batch environment, the RETURN-CODE set by your program becomes the
RC for the JCL job step the program was run under. This is typically what you
want to set and test for.
The RETURN-CODE is set by MOVEing a numeric value to it. For example:
DISPLAY 'No Detail Records found in file.'
MOVE 16 TO RETURN-CODE
GOBACK.
You may also issue a program dump from a program run under Language Environment (IBM
Mainframe option) using
the CEE3DMP--Generate dump
utility.
In older IBM Mainframe COBOL programs, you might see calls to the ILBOABN0 routine. This call
abended your program and issued a dump. This routine is now depreciated in favour of the
technique outlined above.
Finally, really old programs might have code in them to generate abends. This can be done in any number of ways, but division by zero was
often a favourite:
DIVIDE SOME-NUMBER BY ZERO GIVING SOME-NUMBER.
Works every time!
Personally, I recommend setting the RETURN-CODE over calling ILBOABN0 or data-exception tehcniques.
Note: The RETURN-CODE special-register is not part of the COBOL-85 standard. It is available as an IBM extention to the language. You may need to resort to a different mechanism if you are working in a non-IBM compatible environment.
see the following link on how to set the return code passed back to a JCL job step as well as force an Abened code.
http://www.tek-tips.com/viewthread.cfm?qid=1058302&page=22
First, you should check what is accepted by your own shop's/site's working standards. Most teams will already have an accepted way to deliberately abend a program for a 'logic' reason. One company I worked at has a very simple program called SYSABND2, which I believe is written in assembler, which is called just to abend the program.
That said, to ABEND (not just set return code), you should call module CEE3ABD (or previous version ILBOABN0, which is now deprecated).
For details, see:
https://www.ibm.com/support/knowledgecenter/SSLTBW_2.4.0/com.ibm.zos.v2r4.ceea300/clcdump.htm
http://publib.boulder.ibm.com/infocenter/zvm/v5r4/index.jsp?topic=/com.ibm.zos.r9.ceea400/ceea4150320.htm
One method for doing an abnormal end of run is to output a message to the user terminal or to the operator at a mainframe computer centre and possibly to a printer if necessary, all depending on the type of computer the program is to be run on. In cobol it is possible to use DISPLAY UPON .. and use an identifier for the terminal, operator console, or printer as defined in an entry in the SPECIAL-NAMES section of the ENVIRONMENT DIVISION. An example may be similar to this using the correct device names for your case
OPERATOR-CONSOLE IS OUT-OP2 in special-names with DISPLAY "RUN ERROR - NO DETAIL RECORDS, ABORTING" UPON OUT-OP2 and
DISPLAY "REPORT TO OPERATIONS MANAGER" UPON OUT-OP2 and STOP RUN. in procedure division.
A reference to the circumstance would need to be included in any job or macro and operating instructions.
Yes, it is possible to abend your job intentionally through COBOL program by simply calling one module which doesn't exist. It will give S806 abend code.