FBB::CinInserter(3bobcat)
Executing Child Processes
(libbobcat-dev_6.04.00)
2005-2023
NAME
FBB::CinInserter - Runs external programs reading standard input
SYNOPSIS
#include <bobcat/cininserter>
Linking option: -lbobcat
DESCRIPTION
The FBB::CinInserter class offers a basic interface for calling
external programs (so-called child processes) reading their standard input
streams. The standard output and standard error streams of the child processes
by default are not handled by CinInserter objects. The child's standard
input is provided through the CinInserter object: information inserted
into an CinInserter object is forwarded to the child process's standard
input stream. The PATH environment variable is not used when calling child
processes: child process programs must be specified using paths.
CinInserter objects may repeatedly be used to execute the same or
different child processes. Before starting the next child process, the current
child process must have finished.
Arguments passed to child processes may be surrounded by double or single
quotes. Arguments surrounded by double quotes have their double quotes
removed, while interpreting any escape-sequences that may have been used
within. Arguments surrounded by single quotes have their single quotes
removed, while accepting their content as-is. In addition unquoted
escape-sequences may be specified: those escape sequences are evaluated and
replaced by their intended characters (e.g., \100 is converted to @).
When information of undetermined size or structure must be inserted into a
child process then the child process cannot determine when to stop. This
creates an interesting problem: the child process starts, and the parent
process must wait until its child process has finished processing its
input. But input can only be forwarded to the child's input stream after the
child process has started. To solve this problem InterterFork offers an
overloaded execute member, passing information to the child process via a
separate thread.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
INHERITS FROM
FBB::Exec (private),
FBB::OFdBuf (private),
std::ostream.
CONSTRUCTOR
- CinInserter(size_t bufSize = 100):
A bufSize argument may be specified: it defines the internal buffer
size used by the CinInserter's streambuf. By default the stdandard
output and standard error streams are not handled.
- CinInserter(Mode mode, size_t bufSize = 100):
The mode argument must be CinInserter::CLOSE_STD. It indicates
that the standard output and standard error streams are redirected to
/dev/null: any standard output generated by child processes is
ignored. A bufSize argument may be specified: it defines the
internal buffer size used by the CinInserter's streambuf.
Copy and move constructors (and assignment operators) are not available.
DESTRUCTOR
The destructor ends the CinInserter's child process, if it is still
active.
MEMBERS
- void execute(std::string const &cmd):
The argument specifies the command to execute: the command itself must
be specified as a path (the PATH environment variable isn't used). This
member immediately returns, after which information can be inserted into the
CinInserter object which is then forwarded to the childprocess's standard
input stream. See also the description of the next (overloaded execute)
member function.
Once all information has been inserted, the child process's standard input
stream must be closed. This is realized by either calling stop; by
calling execute once again; or by ending the CinInserter object's
lifetime.
Arguments specified in the cmd string are passed to the child process, and
may optionally be specified using single or double quotes, as described in
this man-page's DESCRIPTION section.
- bool execute(std::string const &cmd, std::string const &text):
This member is used to forward a limited amount of information
(contained in the text parameter) to the child process specified at
cmd (defined identically as the cmd parameter of the previous
execute member).
This member returns true if the child process's exit value equals 0.
- int stop():
This function can be called after all information has been inserted
into the CinInserter object to close the child process's standard input
stream. It is not required after calling execute(cmd, text), or when
calling execute again, or when the CinInseror object's lifetime ends.
This member returns the exit code of the last executed child process,
which may also be obtained from the next member:
- int ret() const:
Once a child process has finished this member provides the actual exit
code of the child process. Its value equals -1 before the first exectue
call.
PROTECTED MEMBER
- Pipe &childInPipe():
If derived classes need to override the redirections-members then they
probabaly need access to the pipe read by the child process. This
member provides a reference to that pipe. By default the parent
process inserts information into the pipe, while the
child process reads the inserted information from the pipe.
EXAMPLE
//#include <bobcat/cininserter>
#include "../cininserter"
#include <iostream>
#include <fstream>
using namespace std;
using namespace FBB;
int main()
{
CinInserter inserter;
inserter.execute("/bin/cat");
ifstream in("build");
inserter << in.rdbuf();
cout << "child returns: " << inserter.stop() << '\n';
inserter.execute("/bin/cat");
in.seekg(0); // reset to the beginning
inserter << in.rdbuf();
// when immediately followed by another execute, 'stop' is optional
inserter.execute("/bin/cat", "a simple text\n");
inserter.execute("/bin/cat", "a simple text\n");
bool bret = inserter.execute("/bin/cat", "a simple text\n");
cout << "direct string insertion: " << bret << '\n';
}
FILES
bobcat/cininserter - provides the class interface
SEE ALSO
bobcat(7), cerrextractor(3bobcat), coutextractor(3bobcat),
execl(3), exec(3bobcat),
fork(3bobcat), pipe(3bobcat), process(3bobcat),
stdextractor(3bobcat).
BUGS
None reported.
BOBCAT PROJECT FILES
- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
- bobcat_6.04.00-x.dsc: detached signature;
- bobcat_6.04.00-x.tar.gz: source archive;
- bobcat_6.04.00-x_i386.changes: change log;
- libbobcat1_6.04.00-x_*.deb: debian package containing the
libraries;
- libbobcat1-dev_6.04.00-x_*.deb: debian package containing the
libraries, headers and manual pages;
BOBCAT
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
COPYRIGHT
This is free software, distributed under the terms of the
GNU General Public License (GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).