The FBB::Process class offers an elaborate interface to external
programs and/or scripts from a C++ program (so-called
child-processes). The class offers an easy to use, stream-based interface
to the child process's standard input, standard output and standard error
streams.
Objects of the FBB::Process class use standard process-executing
functions, like sh(1) and members of the execl(1) family to execute
the child process, and allow shell-scripts to be executed as well.
The standard input, output and error streams of executed child processes may
be accessed via their Process parent objects. Input expected by the child
process may be inserted into the Process object, output generated by the
child process may be extracted from the Process object. Process
objects will not be able to access these streams when child processes
themselves redirect their standard streams.
When using (output) redirection with the USE_SHELL path specification (see
below for the path and IOMode specifications) the IGNORE_COUT IOMode (and
possibly IGNORE_CERR) will normally be specified as well.
The same Process object may be used repeatedly to execute the same or
different child processes in sequence. If a previously started child process
is still active it will first be terminated. It is also possible (using the
stop() member) to end a child process explicitly.
Programs to call as child processes may be specified using Process's
constructors. They are not started by the constructor. To start a child
process the start() members or the assignment operator may be used.
Some child processes continue until their standard input streams are
exhausted. The close() member is provided to close such streams.
The class Process should not be used to construct daemons. To create
daemon processes the FBB::Fork class can be used.
Command line arguments passed to child processes may be surrounded by double
or single quotes. Arguments surrounded by double quotes will have their double
quotes removed, interpreting any escape-sequences that may have been used
within. Arguments surrounded by single quotes will have their single quotes
removed, accepting their contents unmodified.
Child processes may be allowed a limited amount of time (in seconds) to
complete. Alternatively, child processes may have no time limit imposed upon
then. A child process will forcefully be terminated when its parent
Process object goes out of scope. Since Process inherits from
FBB::Fork it may use the latter class's member waitForChild() to
prevent premature termination of a child process.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
enum ProcessType:
This enumeration has the following values:
NO_PATH:
This value indicates that the external program should be called as
specified, without searching the elements in the PATH environment
variable.
USE_PATH:
This value indicates that the PATH environment variable should
be used to locate the external program to be executed.
USE_SHELL:
This value indicates that the external program should be called as
a command (using its -c option) to /bin/sh. When
(output) redirection is used with the specified command the
IGNORE_COUT IOMode (and possibly the IGNORE_CERR IOMode as
well) should be specified.
enum IOMode:
The IOMode specification is used to define which of the standard
streams used by child processes are accessed through the Process
object. Sensible combinations may be formed using the bit_or operator.
This enumeration defines the following values:
CIN:
This value indicates that information inserted into the
Process object should be forwared to its child process. If this is not
required then the CIN specification can be omitted.
CERR:
This value indicates that information written by the child process
to its standard error stream should be accessible through the
FBB::Process::cerr() member. If this is not required then the CERR
specification can be omitted.
COUT:
This value indicates that information extracted from the
Process object should be the information written by the child process to
its standard output stream. If this is not required then the COUT
specification can be omitted.
IGNORE_ALL:
This value indicates that the Process object will not extract
information from or insert information into the standard streams of its child
process. It is ignored if any other specification is provided as well.
IGNORE_CERR:
This value indicates that information written by the child process
to its standard error stream should be sent to /dev/null. This
specification is ignored when either CERR or MERGE_COUT_CERR is
specified.
IGNORE_COUT:
This value indicates that information written by the child process
to its standard output stream should be sent to /dev/null. This
specification is ignored when either COUT or MERGE_COUT_CERR is
specified.
MERGE_COUT_CERR:
This value indicates that information extracted from the
Process object should be the information written by the child process to
its standard output or error streams.
enum ChildOutput:
The ChildOutput enumeration defines values returned by the
available() member (see below) indicating to which standard stream the
child process has written information. This enumeration defines the following
values:
NOTHING_AVAILABLE:
This value indicates that the child process did not (yet) write any
information to its standard streams;
CHILD_COUT:
This value indicates that the child process did write
information to its standard output stream which is waiting for extraction.
CHILD_CERR:
This value indicates that the child process did write
information to its standard error stream which is waiting for extraction.
The latter two values may be combined using the bit_or operator
indicating that information on both standard streams is available.
TYPE
IOMode:
Combinations of values of the enum IOMode may be used as value of a
variable of this type. In functions expecting an IOMode argument the empty
set should not normally be specified. To specify multiple IOMode values
the bit_or operator should be used.
PROCESS PARAMETERS
When running a child process three process parameters may be specified: the
child streams to access from the Process object (as an IOMode value);
the way to locate or start the child program (as a ProcessType value); and
the maximum time (in seconds) the child program is allowed to run.
Unless specified otherwise, all the child's standard streams (standard
input, output and error) will be accessible from the Parent process; the
PATH environment variable will not be used to locate the child program
to be executed (often resulting in the requirement to provide an absolute path
to the intended program) and the child processes will be allowed unlimited
time to run.
Following the construction of a Process object all default parameter
values may be modified. Process parameters may be altered for a single process
or the general defaults may be modified. The setXXX() members (see below)
may be used to change the default process parameters. When process parameters
are specified otherwise they will be active for the next process only.
CONSTRUCTORS
The command that may be provided to the following constructors may be the
(initial part of the) specification of an external program to run. When the
program is eventually started it may start and end with a back-tick
(`). The back-ticks will be removed just before the specified program is
executed.
A child process is not started automatically following the object
construction. A start() member or the assignment operator (see below) can
be used to start the specified child process.
Process(std::string const &cmd = ""):
This constructor can also be used as default constructor. It can be
used to specify the (initial part of a) command to execute from a
Process object. Standard default values are used for the process
parameters (see section PROCESS PARAMETERS).
Process(IOMode mode, std::string const &cmd = ""):
This constructor requires the specification of the object's initial
default IOMode setting and it can be used to specify the (initial part of
a) command to execute from a Process object. Standard default values
are used for the remaining two process parameters ((NO_PATH) and no time
limit imposed on the child process).
Process(IOMode mode, ProcessType type, std::string const &cmd = ""):
This constructor requires the specification of the object's initial
default IOMode setting and ProcessType and it can be used to specify
the (initial part of a) command to execute from a Process object. By
default no time limit will be imposed upon the child process.
Process(IOMode mode, ProcessType type, size_t timeLimit,
std::string const &cmd = ""):
This constructor requires the specification of the object's initial
default IOMode setting, ProcessType and time limit imposed upon child
processes it can be used to specify the (initial part of a) command to execute
from a Process object. To prevent a time limit from being imposed upon the
child process specify a time limit of 0 (zero).
The class Process does not offer a copy constructor.
OVERLOADED OPERATORS
Process &operator<<(Type value):
This operator will insert value into the child's standard
input stream. I.e., the child process will read value from its standard
input. A value of any type that can be inserted into an ostream can be
inserted into a Process object. Nothing happens if the member is used when
the child process has terminated. The behavior of this operator is undefined
unless IOMode CIN was specified.
Process &operator>>(Type value):
This operator will extract value from the child's standard output
stream and optionally (if IOMode MERGE_COUT_CERR was specified) from the
child's error stream. I.e., value may be extracted from Process
objects. A value of any type that can be extracted from an istream
can be extracted from a Process object. Nothing happens if the member is
used when the child process has terminated. The behavior of this operator is
undefined unless IOMode COUT or MERGE_COUT_CERR was specified.
Process &operator+=(std::string const &):
This operator adds the provided std::string object to the command
specification currenly stored in a Process object. The currently stored
command specification may be redefined using the member setCommand() (see
below). The member operator+=() does not add a separating blank space
between the currently stored command specification and the text to append. It
merely adds its right-hand side string to the command stored so far. It does
not affect a currently running child process.
int operator=(std::string const &cmd):
The operator=() member defines cmd as the stored command in
a Process object. If the command starts and ends with a back-tick
(`) then the back-ticks are removed, and the resulting contents are
interpreted as a command to execute.
Next it will call stop() (see below) to end any ongoing process
followed by calling start() to execute the newly defined command using the
current default process parameters. It returns stop()'s return value.
Process &operator()(iomode mode):
This operator changes the IOMode of the next child process. It
returns the Process object allowing constructions like
process(COUT) = "/bin/cat";
to start a new child process with the specified IOMode.
Process &operator()(iomode mode, ProcessType type):
This operator changes the IOMode and ProcessType process
parameters of the next child process.
Process &operator()(iomode mode, ProcessType type, size_t timeLimit):
This operator changes all three process parameters of the next child
process. Time limit 0 prevents a time limit from being imposed upon the next
child process.
The default overloaded assignment operator is not available.
MEMBERS
bool active():
This member returns true if the child process is currently running
and false if not. It is automatically called from the insertion and
extraction operators and from the cerr() member but is available as a
public member as well. It may terminate the child process if the child process
has timed out.
size_t available():
This member returns immediately. Its return value indicates whether
any information can be obtained from the child process as value(s) from the
enum ChildOutput. NOTHING_AVAILABLE is returned if no information is
ready for extraction. CHILD_COUT is returned if information from the child
process's standard output stream is available; CHILD_CERR is returned if
information from the child process's standard error stream is available;
CHILD_COUT | CHILD_CERR is returned if information from both the standard
output and standard error streams is available.
std::istream &cerr():
This member may be used to extract information written by the child
process to its standard error stream. This member should only be used when
IOMode CERR was specified for the currently running child process;
otherwise its behavior is undefined.
void close():
This member may be called from the parent process to close the child's
input stream. In situations where the child continuously reads information
from its standard input stream this member must be used to inform the child
process that input has terminated. This member should only be used when
IOMode CIN was specified for the currently running child process;
otherwise its behavior is undefined.
iomode ioMode() const:
This member returns the current default IOMode. Note that the
actualIOMode that will be used may be different from the default
value as the actual value may have been altered using a function call
operator (see operator() above).
ProcessType processType() const:
This member returns the current default ProcessType. Note that the
actualProcessType that will be used may be different from the default
value as the actual value may have been altered using a function call operator
(see operator() above).
size_t timeLimit() const:
This member returns the current default child process time limit. Note
that the actual time limit that will be used may be different from
the default value as the actual value may have been altered using a function
call operator (see operator() above).
void setCommand(std::string const &cmd):
The setCommand() member (re)defines the (initial part of a) command
specification currently stored in an Process object. When the program is
eventually started it may start and end with a back-tick (`). The
back-ticks will be removed just before the specified program is executed.
The setCommand() member will not start the specified command and
operator+=() may be used to append the command specification before the
command is eventually executed. Also, this member does not affect a currently
running child process.
void setIOMode(iomode mode):
This member will change the current default IOMode process
parameter of child processes.
void setProcessType(ProcessType type):
This member will change the current default ProcessType process
parameter of child processes.
void setTimeLimit(size_t timeLimit):
This member will change the current default time limit process
parameter of child processes. No time limit will be imposed upon child
processes if timeLimit 0 is specified.
int start():
The currently specified command is executed using the currently active
process parameters. These process parameters may be modified (either as new
defaults or for the next process only) using overloaded start() members,
the system() members, function call operator or various
set-members.
Having specified a command to execute, the first white-space delimited
element of the specified command is used as the name of the program to
execute. If the program should be called as a command to be executed by
sh(1), the USE_SHELL ProcessType or a system() member
should be used.
If a child process does not terminate by itself (within its allotted
amount of time) it is terminated when it has run for its alloted time; when
the Process object's start() or stop() members are called; when
the object's assignment operator is used; or when the object goes out of
scope.
int start(IOMode mode):
The currently specified command is executed using the specified
IOMode rather than the currently specified default but otherwise using the
currently specified default process parameters. The specified IOMode will
only be used for the process executed by this start() member.
int start(IOMode mode, Program program):
The currently specified command is executed using the specified
IOMode and ProcessType as well as the currently specified child
process time limit. The specified arguments will only be used for the process
executed by this start() member.
int start(IOMode mode, Program program, size_t timeLimit):
The currently specified command is executed using the specified
arguments for the process parameters. The specified arguments will only be
used for the process executed by this start() member.
std::string const &str() const:
This member returns the text of the command currently stored in the
Process object. It shows the command as it will be executed by
start(), system() or the assignment operator. If the command's first
and last characters are back-ticks (`) then those back-ticks will be
removed when the command is actually executed.
void system():
This member executes the currently stored command as a command to
sh(1) (therefore executing the command as a shell command). When using
system() redirections can be included in the command itself (although this
might render the redirected streams implied by the current IOMode)
useless. The currently set process parameters are used when sh(1) is
executed. Calling system() implies calling start().
void system(IOMode mode):
This member executes the currently stored command as a command to
sh(1) (cf. system() above) using the specified IOMode rather than
the current default IOMode setting. The currently specified default time
limit, however, will be used when executing the sh(1) process.
void system(IOMode mode, size_t timeLimit):
This member executes the currently stored command as a command to
sh(1) (cf. system() above) using the specified IOMode and time
limit values rather than their current default settings.
int stop():
This member terminates a currently active child process. The child
process is twice sent a SIG_TERM signal, followed by a SIG_KILL
signal. This member's return value is the exit-value of the child process
that was stopped. It is underfined if it was called without a running child
process.
Following stop() a new command may be called using start(),
system() or the assignment operator (see earlier). Those members will first
call stop() so when the intention is to start another child process
calling stop() can be skipped. Also, stop() is called when the
Process object goes out of scope.
int waitForChild():
This member is inherited from the class FBB::Fork and will wait
for a child process to finish. It can be used to prevent premature termination
of a child process before calling stop(). It is not always required to use
waitForChild(). E.g., when a process writes to its standard output stream
and all output has been read then the child process can be stopped without
calling waitForChild().
EXAMPLE
#include "../process"
#include <string>
#include <iostream>
using namespace std;
using namespace FBB;
void prompt(char const *task)
{
cout << "Press Enter to start " << task << endl;
cin.ignore(INT_MAX, '\n');
}
int main(int argc, char **argv)
try
{
string line;
Process process(Process::CIN | Process::COUT,
"/usr/bin/sha1sum");
prompt("sha1sum");
process.start();
process << "Hello world\n"; // input to sha1sum
process.close();
process >> line; // retrieve the value
cout << line << endl;
process.stop();
if (argc > 1) // sending an e-mail
{
cout << "Sending mail to " << argv[1] << endl;
prompt("/usr/bin/mail");
process.setCommand("/usr/bin/mail -s 'from Process' ");
process += argv[1];
process.start(Process::CIN);
process << "This mail was sent by the process drive\n";
process << "It consists of multiple lines of text\n";
process.close();
process.waitForChild();
}
prompt("5 seconds IO to /bin/cat");
process.setTimeLimit(5); // change time limit
process = "/bin/cat";
while (process.active())
{
cout << "? ";
getline(cin, line);
process << line << endl; // to /bin/cat
line.clear();
if (!getline(process, line)) // from /bin/cat
break;
cout << "Received: " << line << endl;
}
cout << "/bin/cat forcefully terminated\n";
process.setTimeLimit(0);
for (size_t trial = 0; trial < 5; ++trial)
{
prompt("ls");
process(Process::COUT) = "/bin/ls";
cerr << process.str() << endl;
size_t count = 0;
while (getline(process, line))
cout << ++count << ": " << line << endl;
}
}
catch (Errno const &err)
{
cerr << "EXCEPTION CAUGHT: " << err.what() << endl;
return 1;
}
catch (...)
{
cerr << "Unrecognized exception in main()\n";
return 0;
}
With the release of Bobcat 1.21.1 the class Process was completely
rewritten. The new implementation, however, should not affect existing
programs other than that Process will no longer impose a limited
time-to-live upon child processes. The interface was enlarged, but this should
not affect existing programs. The internal organization of the Process
class has changed though, requiring recompilation of sources defining
Process class type objects and linking dynamically to the Bobcat
library.
DISTRIBUTION FILES
bobcat_2.02.03-x.dsc: detached signature;
bobcat_2.02.03-x.tar.gz: source archive;
bobcat_2.02.03-x_i386.changes: change log;
libbobcat1_2.02.03-x_*.deb: debian package holding the
libraries;
libbobcat1-dev_2.02.03-x_*.deb: debian package holding the
libraries, headers and manual pages;
http://sourceforge.net/projects/bobcat: public archive location;
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).