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Standard input is a stream from which a program reads its input data. The program requests data transfers by use of the read operation. Not all programs require stream input. For example, the dir and ls programs (which display file names contained in a directory) may take command-line arguments, but perform their operations without any stream ...
This allows combining multiple commands into a data processing pipeline. Although the final output can be very complex, only a limited number of simple commands are needed to produce it. If not specified, the standard streams (stdin, stdout, and stderr) are assumed. Data sent to stdout are printed to the screen by default but are easily ...
Alternatively, if the drain does not need to read any input from stdin to do something useful, it can be given < /dev/null as input. As all components of a pipe are run in parallel, a shell typically forks a subprocess (a subshell) to handle its contents, making it impossible to propagate variable changes to the outside shell environment.
This example shows tee being used to bypass an inherent limitation in the sudo command. sudo is unable to pipe the standard output to a file. By dumping its stdout stream into /dev/null, we also suppress the mirrored output in the console. The command above gives the current user root access to a server over ssh, by installing the user's public ...
In these languages, including the line __DATA__ (Perl) or __END__ (Ruby, old Perl) marks the end of the code segment and the start of the data segment. Only the contents prior to this line are executed, and the contents of the source file after this line are available as a file object: PACKAGE::DATA in Perl (e.g., main::DATA) and DATA in Ruby ...
More generally, Python 2.x specifies the built-in file objects as being “implemented using C's stdio package [46],” and frequent reference is made to C standard library behaviors; the available operations (open, read, write, etc.) are expected to have the same behavior as the corresponding C functions (fopen, fread, fwrite, etc.).
Types can be read and compared—types are instances of type. The attributes of an object can be extracted as a dictionary. Operators can be overloaded in Python by defining special member functions—for instance, defining a method named __add__ on a class permits one to use the + operator on objects of that class.
For example, C++ functions called from C may not (in general) include reference parameters or throw exceptions. FFIs may be complicated by the following considerations: If one language supports garbage collection (GC) and the other does not; care must be taken that the non-GC language code does nothing to cause GC in the other to fail.