FBB::CinInserter(3bobcat) Executing Child Processes FBB::CinInserter(3bobcat)

FBB::CinInserter - Runs external programs reading standard input

#include <bobcat/cininserter>
Linking option: -lbobcat

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.

All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

FBB::Exec (private), FBB::OFdBuf (private), std::ostream.

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.

The destructor ends the CinInserter’s child process, if it is still active.

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.

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.

//#include <bobcat/cininserter>
#include "../cininserter"
#include <iostream>
#include <fstream>
using namespace std;
using namespace FBB;
int main()

CinInserter inserter;
ifstream in("build");
inserter << in.rdbuf();
cout << "child returns: " << inserter.stop() << ’\n’;
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’; }

bobcat/cininserter - provides the class interface

bobcat(7), cerrextractor(3bobcat), coutextractor(3bobcat), execl(3), exec(3bobcat), fork(3bobcat), pipe(3bobcat), process(3bobcat), stdextractor(3bobcat).

None reported.

https://fbb-git.gitlab.io/bobcat/: gitlab project page;
bobcat_6.02.02-x.dsc: detached signature;
bobcat_6.02.02-x.tar.gz: source archive;
bobcat_6.02.02-x_i386.changes: change log;
libbobcat1_6.02.02-x_*.deb: debian package containing the libraries;
libbobcat1-dev_6.02.02-x_*.deb: debian package containing the libraries, headers and manual pages;

Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.

This is free software, distributed under the terms of the GNU General Public License (GPL).

Frank B. Brokken (f.b.brokken@rug.nl).

2005-2022 libbobcat-dev_6.02.02