NAME¶
Net::Remctl::Backend - Helper infrastructure for remctl backend programs
SYNOPSIS¶
use Net::Remctl::Backend;
my %commands = (
cmd1 => { code => \&run_cmd1 },
cmd2 => { code => \&run_cmd2 },
);
my $backend = Net::Remctl::Backend->new({
commands => \%commands,
});
exit $backend->run();
DESCRIPTION¶
Net::Remctl::Backend provides a framework for remctl backend commands (commands
run by
remctld). It can be configured with a list of supported
subcommands and handles all the command-line parsing and syntax checking,
dispatching the command to the appropriate sub if it is valid.
CLASS METHODS¶
- new(CONFIG)
- Create a new backend object with the given configuration. CONFIG should be
an anonymous hash with one or more of the following keys:
- command
- If set, defines the base remctl command implemented by this backend. The
primary use of this string is in usage and help output. If set, it will be
added to the beginning of each command syntax description so that the help
output will match the remctl command that the user actually runs.
- commands
- The value of this key should be an anonymous hash describing all of the
commands that are supported. See below for the supported keys in the
command configuration.
- help_banner
- If set, the value will be displayed as the first line of help output.
Recommended best practice is to use a string of the form:
<service> remctl help:
where <service> is something like "Event handling" or
"User database" or whatever this set of commands generally does
or manipulates.
The commands key, described above, takes a hash of properties for each
subcommand supported by this backend. The possible keys in that hash are:
- args_match
- A reference to an array of regexes that must match the arguments to this
function. Each element of the array is matched against the corresponding
element in the array of arguments, and if the corresponding regular
expression does not match, the command will be rejected with an error
about an invalid argument. Set the regular expression to undef to not
check the corresponding argument.
There is currently no way to check all arguments in commands that take any
number of arguments.
- args_max
- The maximum number of arguments. If there are more than this number of
arguments, run() will die with an error message without running the
command.
- args_min
- The minimum number of arguments. If there are fewer than this number of
arguments, run() will die with an error message without running the
command.
- code
- A reference to the sub that implements this command. This sub will be
called with the arguments passed on the command line as its arguments
(possibly preceded by the options hash if the "options"
parameter is set as described below). It should return the exit status
that should be used by the backend as a whole: 0 for success and some
non-zero value for an error condition. This sub should print to STDOUT and
STDERR to communicate back to the remctl client.
- nested
- If set, indicates that this is a nested command. The value should be a
nested hash of command definitions, the same as the parameter to the
"commands" argument to new(). When this is set, the first
argument to this command is taken to be a subcommand name, which is looked
up in the hash. All of the hash parameters are interpreted the same as if
it were a top-level command.
If this command is called without any arguments, behavior varies based on
whether the "code" parameter is also set alongside the
"nested" parameter. If "code" is set, the command is
called normally, with no arguments. If "code" is not set,
calling this command without a subcommand is treated as an unknown
command.
- options
- A reference to an array of Getopt::Long option specifications. If this
setting is present, the arguments passed to run() will be parsed by
Getopt::Long using this option specification first, before any other
option processing (including checking for minimum and maximum numbers of
arguments, checking the validity of arguments, or replacing arguments with
data from standard input). The result of parsing options will be passed,
as a reference to a hash, as the first argument to the code that
implements this command, with all remaining arguments passed as the
subsequent arguments.
For example, if this is set to "['help|h', 'version|v']" and the
arguments passed to run() are:
command -hv foo bar
then the code implementing "command" will be called with the
following arguments:
{ help => 1, version => 1 }, 'foo', 'bar'
Getopt::Long will always be configured with the options
"bundling", "no_ignore_case", and
"require_order". This means, among other things, that the first
non-option argument will stop option parsing and all remaining arguments
will be passed through verbatim.
If Getopt::Long rejects the options (due to an unknown option or an invalid
argument to an option, for example), run() will die with the error
message from Getopt::Long without running the command.
- stdin
- Specifies that one argument to this function should be read from standard
input. All of the data on standard input until end of file will be read
into memory, and that data will become the argument number given by the
value of this key is the argument (based at 1). So if this property is set
to 1, the first argument will be the data from standard input, and any
other arguments will be shifted down accordingly. The value may be -1, in
which case the data from standard input will become the last argument, no
matter how many arguments there currently are.
Checks for the number of arguments and for the validity of arguments with
regular expression verification are done after reading the data from
standard input and transforming the argument list accordingly.
- summary
- The summary of what this subcommand does, as text. Ideally, this should
fit on the same line with the syntax after the help output has been laid
out in columns. If it is too long to fit, it will be wrapped, with each
subsequent line indented to the column where the summaries start.
If this key is omitted, the subcommand will still be shown in help output,
provided that it has a syntax key, but without any trailing summary.
- syntax
- The syntax of this subcommand. This should be short, since it needs to fit
on the same line as the summary of what this subcommand does. Both the
command and subcommand should be omitted; the former will be set by the
command parameter to the new() constructor for
Net::Remctl::Backend, and the latter will come from the command itself. A
typical example will look like:
syntax => '<object>'
which will result in help output (assuming command is set to
"object" and this parameter is set on the "delete"
command) that looks like:
object delete <object>
Use abbreviations heavily to keep this string short so that the help output
will remain readable.
Set this key to the empty string to indicate that this subcommand takes no
arguments or flags.
If this key is omitted, the subcommand will be omitted from help
output.
INSTANCE METHODS¶
- help()
- Returns the formatted help summary for the commands supported by this
backend. This is the same as would be printed to standard output in
response to the command "help" with no arguments. The output
will consist of the syntax and summary attributes for each command that
has a syntax attribute defined, as described above under the command
specification. It will be wrapped to 80 columns.
- run([COMMAND[, ARG ...]])
- Parse the command line and perform the appropriate action. The return
value will be the return value of the command run (if any), which should
be the exit status that the backend script should use.
The command (which is the remctl subcommand) and arguments can be passed
directly to run() as parameters. If no arguments are passed,
run() expects @ARGV to contain the parameters passed to the backend
script. Either way the first argument will be the subcommand, used to find
the appropriate command to run, and any remaining arguments will be
arguments to that command. (Note that if the "options" parameter
is set, the first argument passed to the underlying command will be the
options hash.)
If there are errors in the parameters to the command, run() will die
with an appropriate error message.
DIAGNOSTICS¶
Since Net::Remctl::Backend is designed to handle command line parsing for a
script and report appropriate errors if there are problems with the argument,
its
run() method may die with various errors. The possible errors are
listed below. All will be terminated with a newline so the Perl context
information won't be appended.
- %s: insufficient arguments
- The given command was configured with a "args_min" parameter,
and the user passed in fewer arguments than that.
- %s: invalid argument: %s
- The given argument to the given command failed to match a regular
expression that was set with an "args_match" parameter.
- %s: too many arguments
- The given command was configured with a "args_max" parameter,
and the user passed in more arguments than that.
COMPATIBILITY¶
This module was added in the 3.4 release of remctl. Since 3.5, the module
version matches the remctl version but with a leading zero added so that the
minor version always has two numbers (so Net::Remctl::Backend 3.05 was
included in remctl 3.5).
All currently-supported methods and options have been supported since the
original release of the module.
BUGS¶
There is no way to check all arguments with a regex when the command supports
any number of arguments.
AUTHOR¶
Russ Allbery <eagle@eyrie.org>
COPYRIGHT AND LICENSE¶
Copyright 2012, 2013, 2014 The Board of Trustees of the Leland Stanford Junior
University
Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
sell copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
SEE ALSO¶
remctld(8)
The current version of this module is available from its web page at
<
http://www.eyrie.org/~eagle/software/remctl/>.