# FBB::CerrExtractor(3bobcat)

## Executing Child Processes
(libbobcat-dev_6.02.02)

## 2005-2022

## NAME

FBB::CerrExtractor - Runs external programs writing standard error

## SYNOPSIS

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

## DESCRIPTION

The FBB::CerrExtractor class offers a basic interface for calling external programs (so-called child processes) writing their standard error streams. The standard input and standard output streams of the child processes are by default not handled by CerrExtractor objects. The child's standard error is read through the CerrExtractor object: information written by the child process to its standard error stream is extracted or read from CerrExtractor object. The PATH environment variable is not used when calling child processes: child process programs must be specified using paths.

CerrExtractor objects may repeatedly be used to execute the same or different child processes.

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 @).

## 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::IFdBuf (private), std::istream

## CONSTRUCTOR

- CerrExtractor(size_t bufSize = 100):
  A bufSize argument may be specified: it defines the internal buffer size used by the CerrExtractor's streambuf. By default the standard input and standard output streams are not handled.

- CerrExtractor(Mode mode, size_t bufSize = 100):
  The mode argument must be CerrExtractor::CLOSE_STD. It indicates that the standard input and standard error streams are redirected to /dev/null: the child processes cannot read their standard input streams and 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.

## MEMBERS

- void execute(std::string const &cmd):
  The argument specifies the command to execute: the command itself must be specified using an absolute path (the PATH environment variable isn't used). This member immediately returns, after which information written by the child process to its standard error stream may be extracted from the CerrExtractor object.

  Once execute has returned it can be called again, either using the same or another command.

  Arguments passed to the program to be executed as child process may optionally be specified using single or double quotes, as described in this man-page's DESCRIPTION section.

- int ret() const:
  Once execute has returned this member provides the actual exit code of the child process. Its value equals -1 before the first exectue call.

## PROTECTED MEMBER

- Pipe &childOutPipe():
  If derived classes need to override the redirections-members then they probabaly need access to the pipe written by the child process. This member provides a reference to that pipe. By default the parent process reads information from the pipe, while the child process inserts its standard error output into the pipe.

## EXAMPLE

    #include <iostream>

    #include <bobcat/cerrextractor>

    using namespace std;
    using namespace FBB;

    int main()
    {
        CerrExtractor extractor;

        extractor.execute("/bin/cat driver.cc");

        cout << extractor.rdbuf();

        cerr << "Returning: " << extractor.ret() << "\n"
                "again:\n";

        extractor.execute("/bin/cat driver.cc");

        cout << extractor.rdbuf();

        cerr << "Returning: " << extractor.ret() << '\n';

    }

## FILES

bobcat/cerrextractor - provides the class interface

## SEE ALSO

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

## BUGS

None reported.

## BOBCAT PROJECT FILES

- 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

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).