Section: Linux Programmer's Manual (3)
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popen, pclose - process I/O
FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
function opens a process by creating a pipe, forking, and invoking the
shell. Since a pipe is by definition unidirectional, the
argument may specify only reading or writing, not both; the resulting
stream is correspondingly read-only or write-only.
argument is a pointer to a null-terminated string containing a shell
command line. This command is passed to
flag; interpretation, if any, is performed by the shell. The
argument is a pointer to a null-terminated string which must be either `r'
for reading or `w' for writing.
The return value from
is a normal standard I/O stream in all respects save that it must be closed
Writing to such a stream writes to the standard input of the command; the
command's standard output is the same as that of the process that called
unless this is altered by the command itself. Conversely, reading from a
``popened'' stream reads the command's standard output, and the command's
standard input is the same as that of the process that called
Note that output
streams are fully buffered by default.
function waits for the associated process to terminate and returns the exit
status of the command as returned by
function returns NULL if the
calls fail, or if it cannot allocate memory.
function returns -1 if
returns an error, or some other error is detected.
function does not set
if memory allocation fails. If the underlying
is set appropriately. If the
argument is invalid, and this condition is detected,
is set to
cannot obtain the child status,
is set to
Since the standard input of a command opened for reading shares its seek
offset with the process that called
if the original process has done a buffered read, the command's input
position may not be as expected. Similarly, the output from a command
opened for writing may become intermingled with that of the original
process. The latter can be avoided by calling
Failure to execute the shell is indistinguishable from the shell's failure
to execute command, or an immediate exit of the command. The only hint is
an exit status of 127.
function appeared in Version 7 AT&T UNIX.
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
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