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process.3bobcat

NAME

FBB::Process - Runs external programs

SYNOPSIS

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

DESCRIPTION

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.

INHERITS FROM

FBB::Fork(3bobcat) (private),
FBB:IOStream(3bobcat)

ENUMERATIONS

enum ProcessType:
This enumeration has the following values:

o

NO_PATH:
This value indicates that the external program should be called as specified, without searching the elements in the PATH environment variable.

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USE_PATH:
This value indicates that the PATH environment variable should be used to locate the external program to be executed.

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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:

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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.

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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.

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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.

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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.

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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.

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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.

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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:

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NOTHING_AVAILABLE:
This value indicates that the child process did not (yet) write any information to its standard streams;

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CHILD_COUT:
This value indicates that the child process did write information to its standard output stream which is waiting for extraction.

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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

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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.

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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).

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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).

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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.

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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

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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.

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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.

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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.

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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.

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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.

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Process &operator()(iomode mode, ProcessType type):
This operator changes the IOMode and ProcessType process parameters of the next child process.

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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

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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.

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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.

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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.

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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.

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iomode ioMode() const:
This member returns the current default IOMode. Note that the actual IOMode 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).

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ProcessType processType() const:
This member returns the current default ProcessType. Note that the actual ProcessType 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).

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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).

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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.

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void setIOMode(iomode mode):
This member will change the current default IOMode process parameter of child processes.

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void setProcessType(ProcessType type):
This member will change the current default ProcessType process parameter of child processes.

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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.

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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.

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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.

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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.

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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.

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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.

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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().

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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.

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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.

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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.

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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 <bobcat/process>
 #include <string>
 #include <iostream>
 #include <climits>
 
 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;
 }
 
 

FILES

bobcat/process - defines the class interface

SEE ALSO

bobcat(7), execle(3), fork(3bobcat), iostream(3fork), sh(1)

BUGS

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

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bobcat_2.08.01-x.dsc: detached signature;

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bobcat_2.08.01-x.tar.gz: source archive;

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bobcat_2.08.01-x_i386.changes: change log;

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libbobcat1_2.08.01-x_*.deb: debian package holding the libraries;

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libbobcat1-dev_2.08.01-x_*.deb: debian package holding the libraries, headers and manual pages;

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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).

AUTHOR

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