I know May be I was not clear enough of what I am trying to do,
The program is as follows -
Code:
int main()
{
if( write(STDIN_FILENO,"arghh!",6) == -1 )
{
fprintf(stderr,"Error in write\n");
exit(2);
}
return 0;
}
I am doing following on shell command line -
$>file.txt (this create an empty file.txt)
$./a.out < file.txt (redirect standard input of a.out to file.txt, a.out is supposed to WRITE to(not READ from) file.txt(that is what it is programmed to do).
($ is not part of command but of shell command prompt)
STDIN_FILENO's file status flag is 2 (O_RDWR - both read write allowed).
I expected that a.out writes to standard input; which is file.txt. But file.txt remains empty.
I am trying to understand 'why'
Anybody. Please illuminate
Code:
[c_d@localhost cfiles]$ cat temp.c
#include<unistd.h>
#include<fcntl.h>
int main()
{
if((write(STDIN_FILENO,"arrgh!",6))==-1)
{
perror("error writing to file");
}
}
[c_d@localhost cfiles]$ touch file #create empty file
[c_d@localhost cfiles]$ cat file #you can see, that the file is empty
[c_d@localhost cfiles]$ gcc temp.c #compile temp.c
[c_d@localhost cfiles]$ ./a.out 0>file #redirection notice no "arrgh!" prints
[c_d@localhost cfiles]$ cat file #because "arrgh!" is redirected to file
arrgh![c_d@localhost cfiles]$ rm file ; touch file
[c_d@localhost cfiles]$ ./a.out <file # :(
error writing to file: Bad file descriptor
[c_d@localhost cfiles]$
i dunno...why that happens. probably because file connects to stdin of a.out first, so when write command executes, stdin is connected to file so it is not able to write into stdin, hence it returns -1.
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Discussion started by: wisecracker
0 Replies
LEARN ABOUT MOJAVE
open
OPEN(1) BSD General Commands Manual OPEN(1)NAME
open -- open files and directories
SYNOPSIS
open [-e] [-t] [-f] [-F] [-W] [-R] [-n] [-g] [-j] [-h] [-s sdk] [-b bundle_identifier] [-a application] file ... [--args arg1 ...]
DESCRIPTION
The open command opens a file (or a directory or URL), just as if you had double-clicked the file's icon. If no application name is speci-
fied, the default application as determined via LaunchServices is used to open the specified files.
If the file is in the form of a URL, the file will be opened as a URL.
You can specify one or more file names (or pathnames), which are interpreted relative to the shell or Terminal window's current working
directory. For example, the following command would open all Word files in the current working directory:
open *.doc
Opened applications inherit environment variables just as if you had launched the application directly through its full path. This behavior
was also present in Tiger.
The options are as follows:
-a application
Specifies the application to use for opening the file
-b bundle_indentifier
Specifies the bundle identifier for the application to use when opening the file
-e Causes the file to be opened with /Applications/TextEdit
-t Causes the file to be opened with the default text editor, as determined via LaunchServices
-f Reads input from standard input and opens the results in the default text editor. End input by sending EOF character (type Control-D).
Also useful for piping output to open and having it open in the default text editor.
-F Opens the application "fresh," that is, without restoring windows. Saved persistent state is lost, except for Untitled documents.
-W Causes open to wait until the applications it opens (or that were already open) have exited. Use with the -n flag to allow open to func-
tion as an appropriate app for the $EDITOR environment variable.
-R Reveals the file(s) in the Finder instead of opening them.
-n Open a new instance of the application(s) even if one is already running.
-g Do not bring the application to the foreground.
-j Launches the app hidden.
-h Searches header locations for a header whose name matches the given string and then opens it. Pass a full header name (such as NSView.h)
for increased performance.
-s For -h, partial or full SDK name to use; if supplied, only SDKs whose names contain the argument value are searched. Otherwise the high-
est versioned SDK in each platform is used.
--args
All remaining arguments are passed to the opened application in the argv parameter to main(). These arguments are not opened or inter-
preted by the open tool.
EXAMPLES
"open '/Volumes/Macintosh HD/foo.txt'" opens the document in the default application for its type (as determined by LaunchServices).
"open '/Volumes/Macintosh HD/Applications/'" opens that directory in the Finder.
"open -a /Applications/TextEdit.app '/Volumes/Macintosh HD/foo.txt'" opens the document in the application specified (in this case, TextE-
dit).
"open -b com.apple.TextEdit '/Volumes/Macintosh HD/foo.txt'" opens the document in the application specified (in this case, TextEdit).
"open -e '/Volumes/Macintosh HD/foo.txt'" opens the document in TextEdit.
"ls | open -f" writes the output of the 'ls' command to a file in /tmp and opens the file in the default text editor (as determined by
LaunchServices).
"open http://www.apple.com/" opens the URL in the default browser.
"open 'file://localhost/Volumes/Macintosh HD/foo.txt'" opens the document in the default application for its type (as determined by Launch-
Services).
"open 'file://localhost/Volumes/Macintosh HD/Applications/'" opens that directory in the Finder.
"open -h NSView" lists headers whose names contain NSView and allows you to choose which ones to open.
"open -h NSView.h" immediately opens NSView.h.
"open -h NSView -s OSX10.12" lists headers whose names contain NSView in the MacOSX 10.12 SDK and allows you to choose which ones to open.
HISTORY
First appeared in NextStep.
macOS April 14, 2017 macOS
04-01-2009
May be I was not clear enough of what I am trying to do,