Jochen Stenzel > Getopt-ArgvFile-1.11 > Getopt::ArgvFile

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Module Version: 1.11   Source  

NAME ^

Getopt::ArgvFile - interpolates script options from files into @ARGV or another array

VERSION ^

This manual describes version 1.11.

SYNOPSIS ^

One line invocation - option hints are processed while the module is loaded:

  # load module and process option file hints in @ARGV
  use Getopt::ArgvFile default=>1;
   
  # load another module to evaluate the options, e.g.:
  use Getopt::Long;
  ...

  # evaluate options, e.g. this common way:
  GetOptions(\%options, 'any');    # this function is defined in Getopt::Long

Or suppress option hint processing when the module is loaded, to perform it later on:

  # load module, do *not* process option file hints
  use Getopt::ArgvFile justload=>1;
   
  # load another module to evaluate the options, e.g.:
  use Getopt::Long;
  ...

  # *now*, solve option file hints
  Getopt::ArgvFile::argvFile(default=>1);

  # evaluate options, e.g. this common way:
  GetOptions(\%options, 'any');    # this function is defined in Getopt::Long

Or use the traditional two step invocation of module loading with symbol import and explicit option file handling:

  # Load the module and import the &argvFile symbol
  # - this will *not* process option hints.
  # Use *this* syntax to do so, *exactly*.
  use Getopt::ArgvFile qw(argvFile);

  # load another module to evaluate the options, e.g.:
  use Getopt::Long;
  ...

  # *now*, solve option file hints
  argvFile(default=>1);

  # evaluate options, e.g. this common way:
  GetOptions(\%options, 'any');    # this function is defined in Getopt::Long

If options should be processed into another array, this can be done this way:

  # prepare target array
  my @options=('@options1', '@options2', '@options3');

  ...

  # replace file hints by the options stored in the files
  argvFile(array=>\@options);

In case you do not like the "@" prefix it is possible to define an option to be used instead:

  # prepare target array
  my @options=('-options', 'options1', '-options', 'options2');

  ...

  # replace file hints by the options stored in the files
  argvFile(fileOption=>'options', array=>\@options);

DESCRIPTION ^

This module simply interpolates option file hints in @ARGV by the contents of the pointed files. This enables option reading from files instead of or additional to the usual reading from the command line.

Alternatively, you can process any array instead of @ARGV which is used by default and mentioned mostly in this manual.

The interpolated @ARGV could be subsequently processed by the usual option handling, e.g. by a Getopt::xxx module. Getopt::ArgvFile does not perform any option handling itself, it only prepares the array @ARGV.

Option files can significantly simplify the call of a script. Imagine the following:

Breaking command line limits

A script may offer a lot of options, with possibly a few of them even taking parameters. If these options and their parameters are passed onto the program call directly, the number of characters accepted by your shells command line may be exceeded.

Perl itself does not limit the number of characters passed to a script by parameters, but the shell or command interpreter often sets a limit here. The same problem may occur if you want to store a long call in a system file like crontab.

If such a limit restricts you, options and parameters may be moved into option files, which will result in a shorter command line call.

Script calls prepared by scripts

Sometimes a script calls another script. The options passed onto the nested script could depend on variable situations, such as a users input or the detected environment. In such a case, it can be easier to generate an intermediate option file which is then passed to the nested script.

Or imagine two cron jobs one preparing the other: the first may generate an option file which is then used by the second.

Simple access to typical calling scenarios

If several options need to be set, but in certain circumstances are always the same, it could become sligthly nerveracking to type them in again and again. With an option file, they can be stored once and recalled easily as often as necessary.

Further more, option files may be used to group options. Several settings may set up one certain behaviour of the program, while others influence another. Or a certain set of options may be useful in one typical situation, while another one should be used elsewhere. Or there is a common set of options which has to be used in every call, while other options are added depending on the current needs. Or there are a few user groups with different but typical ways to call your script. In all these cases, option files may collect options belonging together, and may be combined by the script users to set up a certain call. In conjunction with the possiblity to nest such collections, this is perhaps the most powerful feature provided by this method.

Individual and installationwide default options

The module allows the programmer to enable user setups of default options; for both individual users or generally all callers of a script. This is especially useful for administrators who can configure the default behaviour of a script by setting up its installationwide startup option file. All script users are free then to completely forget every already configured setup option. And if one of them regularly adds certain options to every call, he could store them in his individual startup option file.

For example, I use this feature to make my scripts both flexible and usable. I have several scripts accessing a database via DBI. The database account parameters as well as the DBI startup settings should not be coded inside the scripts because this is not very flexible, so I implemented them by options. But on the other hand, there should be no need for a normal user to pass all these settings to every script call. My solution for this is to use default option files set up and maintained by an administrator. This is very transparent, most of the users know nothing of these (documented ;-) configuration settings ... and if anything changes, only the option files have to be adapted.

EXPORTS ^

No symbol is exported by default, but you may explicitly import the "argvFile()" function using the exact syntax of the following example:

  use Getopt::ArgvFile qw(argvFile);

Please note that this interface is provided for backwards compatibility with versions up to 1.06. By loading the module this way, the traditional import mechanisms take affect and argvFile() is not called implicitly.

This means that while option file hints are usually processed implicitly when Getopt::ArgvFile is loaded, the syntax

  use Getopt::ArgvFile qw(argvFile);

requires an extra call of argvFile() to process option files.

FUNCTIONS ^

There is only one function, argvFile(), which does all the work of option file hint processing.

Please note that with version 1.07 and above argvFile() is called implicitly when the module is loaded, except this is done in one of the following ways:

  # the traditional interface - provided for
  # backwards compatibility - this loads the
  # module and imports the &argvFile symbol
  use Getopt::ArgvFile qw(argvFile);

  --

  # option file processing is explicitly suppressed
  use Getopt::ArgvFile justload=>1;

Except for the traditional loading, the complete interface of argvFile() is available via use, but in the typical use syntax without parantheses.

  # implicit call of argvFile(default=>1, home=>1)
  use Getopt::ArgvFile default=>1, home=>1;

See ONE LINE INVOCATION for further details.

argvFile()

Scans the command line parameters (stored in @ARGV or an alternatively passed array) for option file hints (see Basics below), reads the pointed files and makes their contents part of the source array (@ARGV by default) replacing the hints.

Because the function was intentionally designed to work on @ARGV and this is still the default behaviour, this manual mostly speaks about @ARGV. Please note that it is possible to process any other array as well.

Basics

An option file hint is simply the filename preceeded by (at least) one "@" character:

  > script -optA argA -optB @optionFile -optC argC

This will cause argvFile() to scan "optionFile" for options. The element "@optionFile" will be removed from the @ARGV array and will be replaced by the options found.

Note: you can choose another prefix by using the "prefix" parameter, see below.

An option file which cannot be found is quietly skipped.

Well, what is within an option file? It is intended to store command line arguments which should be passed to the called script. They can be stored exactly as they would be written in the command line, but may be spread to multiple lines. To make the file more readable, space and comment lines (starting with a "#") are allowed additionally. POD comments are supported as well. For example, the call

  > script -optA argA -optB -optC cArg par1 par2

could be transformed into

  > script @scriptOptions par1 par2

where the file "scriptOptions" may look like this:

  # option a
  -optA argA

  =pod
  option b
  =cut
  -optB

  # option c
  -optC cArg

Nested option files

Option files can be nested. Recursion is avoided globally, that means that every file will be opened only once (the first time argvFile() finds a hint pointing to it). This is the simplest implementation, indeed, but should be suitable. (Unfortunately, there are LIMITS.)

By using this feature, you may combine groups of typical options into a top level option file, e.g.:

  File ab:

  # option a
  -optA argA
  # option b
  -optB

  File c:

  # option c
  -optC cArg

  File abc:

  # combine ab and c
  @ab @c

If anyone provides these files, a user can use a very short call:

  > script @abc

and argvFile() will recursively move all the filed program parameters into @ARGV.

Relative pathes

Pathes in option files might be relative, as in

  -file ../file @../../configs/nested

If written with the (prepared) start directory in mind, that will work, but it can fail when it was written relatively to the option file location because by default those pathes will not be resolved when written from an option file.

Use parameter resolveRelativePathes to switch to path resolution:

   argvFile(resolveRelativePathes=>1);

will cause argvFile() to expand those pathes, both in standard strings and nested option files.

   With resolveRelativePathes, both pathes
   will be resolved:

   -file ../file @../../configs/nested

A path is resolved relative to the option file it is found in.

Environment variables

Similar to relative pathes, environment variables are handled differently depending if the option is specified at the commandline or from an option file, due to bypassed shell processing. By default, argvFile() does not resolve environment variables. But if required it can be commanded to do so via parameter resolveEnvVars.

  argvFile(resolveEnvVars=>1);

Startup support

By setting several named parameters, you can enable automatic processing of startup option files. There are three of them:

The default option file is searched in the installation path of the calling script, the home option file is searched in the users home (evaluated via environment variable "HOME"), and the current option script is searched in the current directory.

By default, all startup option files are expected to be named like the script, preceeded by a dot, but this can be adapted to individual needs if preferred, see below.

 Examples:
  If a script located in "/path/script" is invoked in directory
  /the/current/dir by a user "user" whoms "HOME" variable points
  to "/homes/user", the following happens:

  argvFile()                    # ignores all startup option files;
  argvFile(default=>1)          # searches and expands "/path/.script",
                                # if available (the "default" settings);
  argvFile(home=>1)             # searches and expands "/homes/user/.script",
                                # if available (the "home" settings);
  argvFile(current=>1)          # searches and expands "/the/current/dir/.script",
                                # if available (the "current" settings);
  argvFile(
           default => 1,
           home    => 1,
           current => 1
          )                     # tries to handle all startups.

Any true value will activate the setting it is assigned to.

In case the ".script" name rule does not meet your needs or does not fit into a certain policy, the expected startup filenames can be set up by an option startupFilename. The option value may be a scalar used as the expected filename, or a reference to an array of accepted choices, or a reference to code returning the name - plainly or as a reference to an array of names. Such callback code will be called once and will receive the name of the script.

  # use ".config"
  argvFile(startupFilename => '.config');

  # use ".config" or "config"
  argvFile(startupFilename => [qw(.config config)]);

  # emulate the default behaviour,
  # but use an extra dot postfix
  my $nameBuilder=sub {join('', '.', basename($_[0]), '.');};
  argvFile(startupFilename => $nameBuilder);

  # use .(script)rc or .(script)/config
  my $nameBuilder=sub
                   {
                    my $sname=basename($_[0]);
                    [".${sname}rc", ".${sname}/config"];
                   };
  argvFile(startupFilename => $nameBuilder);

Note that the list variants will use the first matching filename in each possible startup-file path. For example if your array is ['.scriptrc', '.script.config'] and you have both a .scriptrc and a .script.config file in (say) your current directory, only the .scriptrc file will be used, as it is the first found.

The contents found in a startup file is placed before all explicitly set command line arguments. This enables to overwrite a default setting by an explicit option. If all startup files are read, current startup files can overwrite home files which have preceedence over default ones, so that the default startups are most common. In other words, if the module would not support startup files, you could get the same result with "script @/path/.script @/homes/user/.script @/the/current/dir/.script".

Note: There is one certain case when overwriting will not work completely because duplicates are sorted out: if all three types of startup files are used and the script is started in the installation directory, the default file will be identical to the current file. The default file is processed, but the current file is skipped as a duplicate later on and will not overwrite settings made caused by the intermediately processed home file. If started in another directory, it will overwrite the home settings. But the alternative seems to be even more confusing: the script would behave differently if just started in its installation path. Because a user might be more aware of configuration editing then of the current path, I choose the current implementation, but this preceedence might become configurable in a future version.

If there is no HOME environment variable, the home setting takes no effect to avoid trouble accessing the root directory.

Cascades

The function supports multi-level (or so called cascaded) option files. If a filename in an option file hint starts with a "@" again, this complete name is the resolution written back to @ARGV - assuming there will be another utility reading option files.

 Examples:
  @rfile          rfile will be opened, its contents is
                  made part of @ARGV.
  @@rfile         cascade: "@rfile" is written back to
                  @ARGV assuming that there is a subsequent
                  tool called by the script to which this
                  hint will be passed to solve it by an own
                  call of argvFile().

The number of cascaded hints is unlimited.

Processing an alternative array

Although the function was designed to process @ARGV, it is possible to process another array as well if you prefer. To do this, simply pass a reference to this array by parameter array.

 Examples:
  argvFile()                    # processes @ARGV;
  argvFile(array=>\@options);   # processes @options;

Choosing an alternative hint prefix

By default, "@" is the prefix used to mark an option file. This can be changed by using the optional parameter prefix:

 Examples:
  argvFile();                   # use "@";
  argvFile(prefix=>'~');        # use "~";

Note that the strings "#", "=", "-" and "+" are reserved and cannot be chosen here because they are used to start plain or POD comments or are typically option prefixes.

Using an option instead of a hint prefix

People not familiar with option files might be confused by file prefixes. This can be avoided by offering an option that can be used instead of a prefix, using the optional parameter fileOption:

  # install a file option
  # (all lines are equivalent)
  argvFile(fileOption=>'options');
  argvFile(fileOption=>'-options');
  argvFile(fileOption=>'+options');
  argvFile(fileOption=>'--options');

The name of the option can be specified with or without the usual option prefixes -, -- and +.

Once an option is declared, it can replace a prefix. (Prefixes remain in action as well.)

   # with -options declared to be a file option,
   # these sequences are equivalent
   @file
   -options file

   # five equivalent cascades
   @@@@file
   -options @@@file
   -options -options @@file
   -options -options -options @file
   -options -options -options -options file

Please note that prefixes are attached to the filename with no spaces in between, while the option declared via -fileOption is separated from the filename by whitespace, as for normal options.

ONE LINE INVOCATION ^

The traditional two line sequence

  # load the module
  use Getopt::ArgvFile qw(argvFile);

  ...

  # solve option files
  argvFile(default=>1);

can be reduced to one line - just pass the parameters of argvFile() to use():

  # load module and process option file hints in @ARGV
  use Getopt::ArgvFile default=>1;

Please note that in this case option file hints are processed at compile time. This means that if you want to process alternative arrays, these arrays have to be prepared before, usually in a BEGIN block.

In versions 1.07 and above, implicit option file handling is the default and only suppressed for the traditional

  use Getopt::ArgvFile qw(argvFile);

loading, for reasons of backwards compatibility. A simple loading like

  use Getopt::ArgvFile;

will process option hints! If you want to suppress this, use the justload switch:

  use Getopt::ArgvFile justload=>1;

See FUNCTIONS for additional informations.

NOTES ^

If a script calling argvFile() with the default switch is invoked using a relative path, it is strongly recommended to perform the call of argvFile() in the startup directory because argvFile() then uses the relative script path as well.

LIMITS ^

If an option file does not exist, argvFile() simply ignores it. No message will be displayed, no special return code will be set.

AUTHOR ^

Jochen Stenzel <mailto:perl@jochen-stenzel.de>

LICENSE ^

Copyright (c) 1993-2007 Jochen Stenzel. All rights reserved.

This program is free software, you can redistribute it and/or modify it under the terms of the Artistic License distributed with Perl version 5.003 or (at your option) any later version. Please refer to the Artistic License that came with your Perl distribution for more details.

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