.\" Copyright (C) 2010-2017 Colin Watson.

.\"

.\" This file is part of libpipeline.

.\"

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.\" it under the terms of the GNU General Public License as published by

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.\" your option) any later version.

.\"

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.\" WITHOUT ANY WARRANTY; without even the implied warranty of

.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

.\" General Public License for more details.

.\"

.\" You should have received a copy of the GNU General Public License

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.\" USA.

.Dd October 11, 2010

.Os GNU

.ds volume-operating-system GNU

.Dt LIBPIPELINE 3

.Sh NAME

.Nm libpipeline

.Nd pipeline manipulation library

.Sh SYNOPSIS

.In pipeline.h

.Sh DESCRIPTION

.Nm

is a C library for setting up and running pipelines of processes, without

needing to involve shell command-line parsing which is often error-prone and

insecure.

This relieves programmers of the need to laboriously construct pipelines

using lower-level primitives such as

.Ic fork

and

.Ic execve .

.Pp

The general way to use

.Nm

involves constructing a

.Vt pipeline

structure and adding one or more

.Vt pipecmd

structures to it.

A

.Vt pipecmd

represents a subprocess (or

.Dq command ) ,

while a

.Vt pipeline

represents a sequence of subprocesses each of whose outputs is connected to

the next one's input, as in the example

.Ic ls | grep pattern | less .

The calling program may adjust certain properties of each command

independently, such as its environment and

.Xr nice 3

priority, as well as properties of the entire pipeline such as its input and

output and the way signals are handled while executing it.

The calling program may then start the pipeline, read output from it, wait

for it to complete, and gather its exit status.

.Pp

Strings passed as

.Vt const char *

function arguments will be copied by the library.

.Ss Functions to build individual commands

.Bl -tag -width 4n -compact

.It Ft "pipecmd *" Ns Fn pipecmd_new "const char *name"

.Pp

Construct a new command representing execution of a program called

.Va name .

.Pp

.It Ft "pipecmd *" Ns Fn pipecmd_new_argv "const char *name" "va_list argv"

.It Ft "pipecmd *" Ns Fn pipecmd_new_args "const char *name" ...

.Pp

Convenience constructors wrapping

.Fn pipecmd_new

and

.Fn pipecmd_arg .

Construct a new command representing execution of a program called

.Va name

with arguments.

Terminate arguments with

.Li NULL .

.Pp

.It Ft "pipecmd *" Ns Fn pipecmd_new_argstr "const char *argstr"

.Pp

Split

.Va argstr

on whitespace to construct a command and arguments, honouring shell-style

single-quoting, double-quoting, and backslashes, but not other shell

evilness like wildcards, semicolons, or backquotes.

This is included only to support situations where command arguments are

encoded into configuration files and the like.

While it is safer than

.Xr system 3 ,

it still involves significant string parsing which is inherently riskier

than avoiding it altogether.

Please try to avoid using it in new code.

.Pp

.It Vt typedef void pipecmd_function_type (void *) ;

.It Vt typedef void pipecmd_function_free_type (void *) ;

.It Xo Ft "pipecmd *" Ns

.Fo pipecmd_new_function

.Fa "const char *name"

.Fa "pipecmd_function_type *func"

.Fa "pipecmd_function_free_type *free_func"

.Fa "void *data"

.Fc

.Xc

.Pp

Construct a new command that calls a given function rather than executing a

process.

.Pp

The data argument is passed as the function's only argument, and will be

freed before returning using free_func (if

.No non- Ns Va NULL Ns ).

.Pp

.Li pipecmd_*

functions that deal with arguments cannot be used with the command returned

by this function.

.Pp

.It Xo Ft "pipecmd *" Ns

.Fn pipecmd_new_sequencev "const char *name" "va_list cmdv"

.Xc

.It Ft "pipecmd *" Ns Fn pipecmd_new_sequence "const char *name" ...

.Pp

Construct a new command that itself runs a sequence of commands, supplied as

.Vt "command *"

arguments following

.Va name

and terminated by

.Li NULL .

The commands will be executed in forked children; if any exits non-zero then

it will terminate the sequence, as with "&&" in shell.

.Pp

.Li pipecmd_*

functions that deal with arguments cannot be used with the command returned

by this function.

.Pp

.It Ft "pipecmd *" Ns Fn pipecmd_new_passthrough void

.Pp

Return a new command that just passes data from its input to its output.

.Pp

.It Ft "pipecmd *" Ns Fn pipecmd_dup "pipecmd *cmd"

.Pp

Return a duplicate of a command.

.Pp

.It Ft void Fn pipecmd_arg "pipecmd *cmd" "const char *arg"

.Pp

Add an argument to a command.

.Pp

.It Ft void Fn pipecmd_argf "pipecmd *cmd" "const char *format" ...

.Pp

Convenience function to add an argument with printf substitutions.

.Pp

.It Ft void Fn pipecmd_argv "pipecmd *cmd" "va_list argv"

.It Ft void Fn pipecmd_args "pipecmd *cmd" ...

.Pp

Convenience functions wrapping

.Fn pipecmd_arg

to add multiple arguments at once.

Terminate arguments with

.Li NULL .

.Pp

.It Ft void Fn pipecmd_argstr "pipecmd *cmd" "const char *argstr"

.Pp

Split

.Va argstr

on whitespace to add a list of arguments, honouring shell-style

single-quoting, double-quoting, and backslashes, but not other shell

evilness like wildcards, semicolons, or backquotes.

This is included only to support situations where command arguments are

encoded into configuration files and the like.

While it is safer than

.Xr system 3 ,

it still involves significant string parsing which is inherently riskier

than avoiding it altogether.

Please try to avoid using it in new code.

.Pp

.It Ft void Fn pipecmd_get_nargs "pipecmd *cmd"

.Pp

Return the number of arguments to this command.

Note that this includes the command name as the first argument, so the

command

.Sq echo foo bar

is counted as having three arguments.

.Pp

.It Ft void Fn pipecmd_nice "pipecmd *cmd" "int value"

.Pp

Set the

.Xr nice 3

value for this command.

Defaults to 0.

Errors while attempting to set the nice value are ignored, aside from

emitting a debug message.

.Pp

.It Ft void Fn pipecmd_discard_err "pipecmd *cmd" "int discard_err"

.Pp

If

.Va discard_err

is non-zero, redirect this command's standard error to

.Pa /dev/null .

Otherwise, and by default, pass it through.

This is usually a bad idea.

.Pp

.It Ft void Fn pipecmd_chdir "pipecmd *cmd" "const char *directory"

.Pp

Change the working directory to

.Va directory

while running this command.

.Pp

.It Ft void Fn pipecmd_fchdir "pipecmd *cmd" "int directory_fd"

.Pp

Change the working directory to the directory given by the open file

descriptor

.Va directory_fd

while running this command.

.Pp

.It Xo Ft void

.Fn pipecmd_setenv "pipecmd *cmd" "const char *name" "const char *value"

.Xc

.Pp

Set environment variable

.Va name

to

.Va value

while running this command.

.Pp

.It Ft void Fn pipecmd_unsetenv "pipecmd *cmd" "const char *name"

.Pp

Unset environment variable

.Va name

while running this command.

.Pp

.It Ft void Fn pipecmd_clearenv "pipecmd *cmd"

.Pp

Clear the environment while running this command.

(Note that environment operations work in sequence; pipecmd_clearenv

followed by pipecmd_setenv causes the command to have just a single

environment variable set.)

Beware that this may cause unexpected failures, for example if some of the

contents of the environment are necessary to execute programs at all (say,

.Li PATH ) .

.Pp

.It Xo Ft void

.Fo pipecmd_pre_exec

.Fa "pipecmd *cmd"

.Fa "pipecmd_function_type *func"

.Fa "pipecmd_function_free_type *free_func"

.Fa "void *data"

.Fc

.Xc

.Pp

Install a pre-exec handler.

This will be run immediately before executing the command's payload (process

or function).

Pass NULL to clear any existing pre-exec handler.

The data argument is passed as the function's only argument, and will be

freed before returning using free_func (if non-NULL).

.Pp

This is similar to pipeline_install_post_fork, except that is specific to a

single command rather than installing a global handler, and it runs slightly

later (immediately before exec rather than immediately after fork).

.Pp

.It Ft void Fn pipecmd_sequence_command "pipecmd *cmd" "pipecmd *child"

.Pp

Add a command to a sequence created using

.Fn pipecmd_new_sequence .

.Pp

.It Ft void Fn pipecmd_dump "pipecmd *cmd" "FILE *stream"

.Pp

Dump a string representation of a command to stream.

.Pp

.It Ft "char *" Ns Fn pipecmd_tostring "pipecmd *cmd"

.Pp

Return a string representation of a command.

The caller should free the result.

.Pp

.It Ft void Fn pipecmd_exec "pipecmd *cmd"

.Pp

Execute a single command, replacing the current process.

Never returns, instead exiting non-zero on failure.

.Pp

.It Ft void Fn pipecmd_free "pipecmd *cmd"

.Pp

Destroy a command.

Safely does nothing if

.Va cmd

is

.Li NULL .

.El

.Ss Functions to build pipelines

.Bl -tag -width 4n -compact

.It Ft "pipeline *" Ns Fn pipeline_new void

.Pp

Construct a new pipeline.

.Pp

.It Ft "pipeline *" Ns Fn pipeline_new_commandv "pipecmd *cmd1" "va_list cmdv"

.It Ft "pipeline *" Ns Fn pipeline_new_commands "pipecmd *cmd1" ...

.Pp

Convenience constructors wrapping

.Fn pipeline_new

and

.Fn pipeline_command .

Construct a new pipeline consisting of the given list of commands.

Terminate commands with

.Li NULL .

.Pp

.It Xo Ft "pipeline *" Ns

.Fn pipeline_new_command_argv "const char *name" "va_list argv"

.Xc

.It Ft "pipeline *" Ns Fn pipeline_new_command_args "const char *name" ...

.Pp

Construct a new pipeline and add a single command to it.

.Pp

.It Ft "pipeline *" Ns Fn pipeline_join "pipeline *p1" "pipeline *p2"

.Pp

Joins two pipelines, neither of which are allowed to be started.

Discards

.Fa want_out ,

.Fa want_outfile ,

and

.Fa outfd

from

.Va p1 ,

and

.Fa want_in ,

.Fa want_infile ,

and

.Fa infd

from

.Va p2 .

.Pp

.It Ft void Fn pipeline_connect "pipeline *source" "pipeline *sink" ...

.Pp

Connect the input of one or more sink pipelines to the output of a source

pipeline.

The source pipeline may be started, but in that case

.Fn pipeline_want_out

must have been called with a negative

.Fa fd ;

otherwise, calls

.Fn pipeline_want_out source -1 .

In any event, calls

.Fn pipeline_want_in sink -1

on all sinks, none of which are allowed to be started.

Terminate arguments with

.Li NULL .

.Pp

This is an application-level connection; data may be intercepted between the

pipelines by the program before calling

.Fn pipeline_pump ,

which sets data flowing from the source to the sinks.

It is primarily useful when more than one sink pipeline is involved, in

which case the pipelines cannot simply be concatenated into one.

.Pp

The result is similar to

.Xr tee 1 ,

except that output can be sent to more than two places and can easily be

sent to multiple processes.

.Pp

.It Ft void Fn pipeline_command "pipeline *p" "pipecmd *cmd"

.Pp

Add a command to a pipeline.

.Pp

.It Xo Ft void

.Fn pipeline_command_argv "pipeline *p" "const char *name" "va_list argv"

.Xc

.It Ft void Fn pipeline_command_args "pipeline *p" "const char *name" ...

.Pp

Construct a new command and add it to a pipeline in one go.

.Pp

.It Ft void Fn pipeline_command_argstr "pipeline *p" "const char *argstr"

.Pp

Construct a new command from a shell-quoted string and add it to a pipeline

in one go.

See the comment against

.Fn pipecmd_new_argstr

above if you're tempted to use this function.

.Pp

.It Ft void Fn pipeline_commandv "pipeline *p" "va_list cmdv"

.It Ft void Fn pipeline_commands "pipeline *p" ...

.Pp

Convenience functions wrapping

.Fn pipeline_command

to add multiple commands at once.

Terminate arguments with

.Li NULL .

.Pp

.It Ft void Fn pipeline_want_in "pipeline *p" "int fd"

.It Ft void Fn pipeline_want_out "pipeline *p" "int fd"

.Pp

Set file descriptors to use as the input and output of the whole pipeline.

If non-negative,

.Va fd

is used directly as a file descriptor.

If negative,

.Fn pipeline_start

will create pipes and store the input writing half and the output reading

half in the pipeline's

.Fa infd

or

.Fa outfd

field as appropriate.

The default is to leave input and output as stdin and stdout unless

.Fn pipeline_want_infile

or

.Fn pipeline_want_outfile

respectively has been called.

.Pp

Calling these functions supersedes any previous call to

.Fn pipeline_want_infile

or

.Fn pipeline_want_outfile

respectively.

.Pp

.It Ft void Fn pipeline_want_infile "pipeline *p" "const char *file"

.It Ft void Fn pipeline_want_outfile "pipeline *p" "const char *file"

.Pp

Set file names to open and use as the input and output of the whole

pipeline.

This may be more convenient than supplying file descriptors, and guarantees

that the files are opened with the same privileges under which the pipeline

is run.

.Pp

Calling these functions (even with

.Li NULL ,

which returns to the default of leaving input and output as stdin and

stdout) supersedes any previous call to

.Fn pipeline_want_in

or

.Fn pipeline_want_outfile

respectively.

.Pp

The given files will be opened when the pipeline is started.

If an output file does not already exist, it is created (with mode 0666

modified in the usual way by umask); if it does exist, then it is truncated.

.Pp

.It Ft void Fn pipeline_ignore_signals "pipeline *p" "int ignore_signals"

.Pp

If

.Va ignore_signals

is non-zero, ignore

.Li SIGINT

and

.Li SIGQUIT

in the calling process while the pipeline is running, like

.Xr system 3 .

Otherwise, and by default, leave their dispositions unchanged.

.Pp

.It Ft int Fn pipeline_get_ncommands "pipeline *p"

.Pp

Return the number of commands in this pipeline.

.Pp

.It Ft "pipecmd *" Ns Fn pipeline_get_command "pipeline *p" "int n"

.Pp

Return command number

.Va n

from this pipeline, counting from zero, or

.Li NULL

if

.Va n

is out of range.

.Pp

.It Xo Ft "pipecmd *" Ns

.Fn pipeline_set_command "pipeline *p" "int n" "pipecmd *cmd"

.Xc

.Pp

Set command number

.Va n

in this pipeline, counting from zero, to

.Va cmd ,

and return the previous command in that position.

Do nothing and return

.Li NULL

if

.Va n

is out of range.

.Pp

.It Ft pid_t Fn pipeline_get_pid "pipeline *p" "int n"

.Pp

Return the process ID of command number

.Va n

from this pipeline, counting from zero.

The pipeline must be started.

Return

.Li \-1

if

.Va n

is out of range or if the command has already exited and been reaped.

.Pp

.It Ft "FILE *" Ns Fn pipeline_get_infile "pipeline *p"

.It Ft "FILE *" Ns Fn pipeline_get_outfile "pipeline *p"

.Pp

Get streams corresponding to

.Fa infd

and

.Fa outfd

respectively.

The pipeline must be started.

.Pp

.It Ft void Fn pipeline_dump "pipeline *p" "FILE *stream"

.Pp

Dump a string representation of

.Va p

to stream.

.Pp

.It Ft "char *" Ns Fn pipeline_tostring "pipeline *p"

.Pp

Return a string representation of

.Va p .

The caller should free the result.

.Pp

.It Ft void Fn pipeline_free "pipeline *p"

.Pp

Destroy a pipeline and all its commands.

Safely does nothing if

.Va p

is

.Li NULL .

May wait for the pipeline to complete if it has not already done so.

.El

.Ss Functions to run pipelines and handle signals

.Bl -tag -width 4n -compact

.It Vt typedef void pipeline_post_fork_fn (void) ;

.It Ft void Fn pipeline_install_post_fork "pipeline_post_fork_fn *fn"

.Pp

Install a post-fork handler.

This will be run in any child process immediately after it is forked.

For instance, this may be used for cleaning up application-specific signal

handlers.

Pass

.Li NULL

to clear any existing post-fork handler.

.Pp

See pipecmd_pre_exec for a similar facility limited to a single command

rather than global to the calling process.

.Pp

.It Ft void Fn pipeline_start "pipeline *p"

.Pp

Start the processes in a pipeline.

Installs this library's

.Li SIGCHLD

handler if not already installed.

Calls

.Li error (FATAL)

on error.

.Pp

.It Xo

.Ft int Fn pipeline_wait_all "pipeline *p" "int **statuses" "int *n_statuses"

.Xc

.Pp

Wait for a pipeline to complete.

Set

.No * Ns Va statuses

to a newly-allocated array of wait statuses, as returned by

.Xr waitpid 2 ,

and

.No * Ns Va n_statuses

to the length of that array.

The return value is similar to the exit status that a shell would return,

with some modifications.

If the last command exits with a signal (other than

.Li SIGPIPE ,

which is considered equivalent to exiting zero), then the return value is

128 plus the signal number; if the last command exits normally but non-zero,

then the return value is its exit status; if any other command exits

non-zero, then the return value is 127; otherwise, the return value is 0.

This means that the return value is only 0 if all commands in the pipeline

exit successfully.

.Pp

.It Ft int Fn pipeline_wait "pipeline *p"

.Pp

Wait for a pipeline to complete and return its combined exit status,

calculated as for

.Fn pipeline_wait_all .

.Pp

.It Ft int Fn pipeline_run "pipeline *p"

.Pp

Start a pipeline, wait for it to complete, and free it, all in one go.

.Pp

.It Ft void Fn pipeline_pump "pipeline *p" ...

.Pp

Pump data among one or more pipelines connected using

.Fn pipeline_connect

until all source pipelines have reached end-of-file and all data has been

written to all sinks (or failed).

All relevant pipelines must be supplied: that is, no pipeline that has been

connected to a source pipeline may be supplied unless that source pipeline

is also supplied.

Automatically starts all pipelines if they are not already started, but does

not wait for them.

Terminate arguments with

.Li NULL .

.El

.Ss Functions to read output from pipelines

In general, output is returned as a pointer into a buffer owned by the

pipeline, which is automatically freed when

.Fn pipeline_free

is called.

This saves the caller from having to explicitly free individual blocks of

output data.

.Pp

.Bl -tag -width 4n -compact

.It Ft "const char *" Ns Fn pipeline_read "pipeline *p" "size_t *len"

.Pp

Read

.Va len

bytes of data from the pipeline, returning the data block.

.Va len

is updated with the number of bytes read.

.Pp

.It Ft "const char *" Ns Fn pipeline_peek "pipeline *p" "size_t *len"

.Pp

Look ahead in the pipeline's output for

.Va len

bytes of data, returning the data block.

.Va len

is updated with the number of bytes read.

The starting position of the next read or peek is not affected by this call.

.Pp

.It Ft size_t Fn pipeline_peek_size "pipeline *p"

.Pp

Return the number of bytes of data that can be read using

.Fn pipeline_read

or

.Fn pipeline_peek

solely from the peek cache, without having to read from the pipeline itself

(and thus potentially block).

.Pp

.It Ft void Fn pipeline_peek_skip "pipeline *p" "size_t len"

.Pp

Skip over and discard

.Va len

bytes of data from the peek cache.

Asserts that enough data is available to skip, so you may want to check

using

.Fn pipeline_peek_size

first.

.Pp

.It Ft "const char *" Ns Fn pipeline_readline "pipeline *p"

.Pp

Read a line of data from the pipeline, returning it.

.Pp

.It Ft "const char *" Ns Fn pipeline_peekline "pipeline *p"

.Pp

Look ahead in the pipeline's output for a line of data, returning it.

The starting position of the next read or peek is not affected by this call.

.El

.Ss Signal handling

.Nm

installs a signal handler for

.Li SIGCHLD ,

and collects the exit status of child processes in

.Fn pipeline_wait .

Applications using this library must either refrain from changing the

disposition of

.Li SIGCHLD

(in other words, must rely on

.Nm

for all child process handling) or else must make sure to restore

.Nm Ns 's

.Li SIGCHLD

handler before calling any of its functions.

.Pp

If the

.Fa ignore_signals

flag is set in a pipeline (which is the default), then the

.Li SIGINT

and

.Li SIGQUIT

signals will be ignored in the parent process while child processes are

running.

This mirrors the behaviour of

.Xr system 3 .

.Pp

.Nm

leaves child processes with the default disposition of

.Li SIGPIPE ,

namely to terminate the process.

It ignores

.Li SIGPIPE

in the parent process while running

.Fn pipeline_pump .

.Ss Reaping of child processes

.Nm

installs a

.Li SIGCHLD

handler that will attempt to reap child processes which have exited.

This calls

.Xr waitpid 2

with

.Li \-1 ,

so it will reap any child process, not merely those created by way of this

library.

At present, this means that if the calling program forks other child

processes which may exit while a pipeline is running, the program is not

guaranteed to be able to collect exit statuses of those processes.

.Pp

You should not rely on this behaviour, and in future it may be modified

either to reap only child processes created by this library or to provide a

way to return foreign statuses to the application.

Please contact the author if you have an example application and would like

to help design such an interface.

.Sh ENVIRONMENT

If the

.Ev PIPELINE_DEBUG

environment variable is set to

.Dq 1 ,

then

.Nm

will emit debugging messages on standard error.

.Pp

If the

.Ev PIPELINE_QUIET

environment variable is set to any value, then

.Nm

will refrain from printing an error message when a subprocess is terminated

by a signal.

.Sh EXAMPLES

In the following examples, function names starting with

.Li pipecmd_

or

.Li pipeline_

are real

.Nm

functions, while any other function names are pseudocode.

.Pp

The simplest case is simple.

To run a single command, such as

.Ic mv

.Pa source

.Pa dest :

.Bd -literal -offset indent

pipeline *p = pipeline_new_command_args ("mv", source, dest, NULL);

int status = pipeline_run (p);

.Ed

.Pp

.Nm

is often used to mimic shell pipelines, such as the following example:

.Pp

.Dl zsoelim < input-file | tbl | nroff -mandoc -Tutf8

.Pp

The code to construct this would be:

.Bd -literal -offset indent

pipeline *p;

int status;

p = pipeline_new ();

pipeline_want_infile (p, "input-file");

pipeline_command_args (p, "zsoelim", NULL);

pipeline_command_args (p, "tbl", NULL);

pipeline_command_args (p, "nroff", "-mandoc", "-Tutf8", NULL);

status = pipeline_run (p);

.Ed

.Pp

You might want to construct a command more dynamically:

.Bd -literal -offset indent

pipecmd *manconv = pipecmd_new_args ("manconv", "-f", from_code,

                                     "-t", "UTF-8", NULL);

if (quiet)

        pipecmd_arg (manconv, "-q");

pipeline_command (p, manconv);

.Ed

.Pp

Perhaps you want an environment variable set only while running a certain

command:

.Bd -literal -offset indent

pipecmd *less = pipecmd_new ("less");

pipecmd_setenv (less, "LESSCHARSET", lesscharset);

.Ed

.Pp

You might find yourself needing to pass the output of one pipeline to

several other pipelines, in a

.Dq tee

arrangement:

.Bd -literal -offset indent

pipeline *source, *sink1, *sink2;

source = make_source ();

sink1 = make_sink1 ();

sink2 = make_sink2 ();

pipeline_connect (source, sink1, sink2, NULL);

/* Pump data among these pipelines until there's nothing left. */

pipeline_pump (source, sink1, sink2, NULL);

pipeline_free (sink2);

pipeline_free (sink1);

pipeline_free (source);

.Ed

.Pp

Maybe one of your commands is actually an in-process function, rather than

an external program:

.Bd -literal -offset indent

pipecmd *inproc = pipecmd_new_function ("in-process", &func,

                                        NULL, NULL);

pipeline_command (p, inproc);

.Ed

.Pp

Sometimes your program needs to consume the output of a pipeline, rather

than sending it all to some other subprocess:

.Bd -literal -offset indent

pipeline *p = make_pipeline ();

const char *line;

pipeline_want_out (p, -1);

pipeline_start (p);

line = pipeline_peekline (p);

if (!strstr (line, "coding: UTF-8"))

        printf ("Unicode text follows:\n");

while (line = pipeline_readline (p))

        printf ("  %s", line);

pipeline_free (p);

.Ed

.Sh SEE ALSO

.Xr fork 2 ,

.Xr execve 2 ,

.Xr system 3 ,

.Xr popen 3 .

.Sh AUTHORS

.An -nosplit

Most of

.Nm

was written by

.An Colin Watson Aq cjwatson@debian.org ,

originally for use in man\-db.

The initial version was based very loosely on the

.Fn run_pipeline

function in GNU groff, written by

.An James Clark Aq jjc@jclark.com .

It also contains library code by

.An Markus Armbruster ,

and by various contributors to Gnulib.

.Pp

.Nm

is licensed under the GNU General Public License, version 3 or later.

See the README file for full details.

.Sh BUGS

Using this library in a program which runs any other child processes and/or

installs its own

.Li SIGCHLD

handler is unlikely to work.