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HP-UX Reference > P
popen(3S)HP-UX 11i Version 2: December 2007 Update |
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NAMEpopen(), pclose() — initiate pipe I/O to/from a process SYNOPSIS#include <stdio.h> FILE *popen(const char *command, const char *type); int pclose(FILE *stream); DESCRIPTIONpopen() creates a pipe between the calling program and a command to be executed by the POSIX shell, /usr/bin/sh (see sh-posix(1)). The arguments to popen() are pointers to null-terminated strings containing, respectively, a shell command line and an I/O mode, either r for reading or w for writing. popen() returns a stream pointer such that one can write to the standard input of the command if the I/O mode is w by writing to the file stream; and one can read from the standard output of the command if the I/O mode is r by reading from the file stream. A stream opened by popen() should be closed by pclose(), which waits for the associated process to terminate and returns the exit status of the command. Because open files are shared, a type r command can be used as an input filter and a type w command as an output filter. APPLICATION USAGEAfter a stream is associated with a pipe by popen(), the stream is byte-oriented (see orientation(5)). RETURN VALUEpopen() returns a NULL pointer if files or processes cannot be created. The success of the command execution can be checked by examining the return value of pclose(). pclose() returns -1 if stream is not associated with a popen()ed command, or 127 if /usr/bin/sh could not be executed for some reason. WARNINGSIf the original and popen()ed processes concurrently read or write a common file, neither should use buffered I/O because the buffering will not work properly. Problems with an output filter can be forestalled by careful buffer flushing, e.g., with fflush(); see fclose(3S). |
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