eselect Developer Reference

1.  Introduction

About eselect

eselect is a framework for simplyfying and introducing consistency to the various foo-config and blah-update tools. It is an option for developers who don't like reinventing the wheel, not a mandatory tool.

2.  Getting Started

Introduction

When porting your application to use the eselect framework, you will generally need to create a module. Often this can be heavily based upon an existing module, so check to see whether there is something that does almost what you need first (symlink handling is a good example of something that can be copied rather than reinvented).

A Simple Module

It's easiest to illustrate by example. Here's a simple module, named cow.eselect. It has two actions, moo and think, plus the standard help, usage and version actions, and is installed to $(datadir)/eselect/modules/.

# Copyright 1999-2005 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id: $

DESCRIPTION="Do things to a cow"
MAINTAINER="foo@gentoo.org"
SVN_DATE='$Date: $'
VERSION=$(svn_date_to_version "${SVN_DATE}")

### moo action

describe_moo() {
	echo "Say moo"
}

describe_moo_parameters() {
  echo "<text>"
}

describe_moo_options() {
  echo "text : Text to display (optional)"
  echo "--dead : Use a dead cow"
  echo "--borg : Use a borged cow"
}


do_moo() {
  local params=
  while [[ ${1#--} != ${1} ]] ; do
    if [[ "--dead" == ${1} ]] ; then
      shift
      params="${params} -d"
    elif [[ "--borg" == "${1}" ]] ; then
      shift
      params="${params} -b"
    elif [[ "--" == "${1}" ]] ; then
      break
    else
      die -q "Unknown parameter ${1}"
    fi
  done

  echo "${@:-I am a cow}" | cowsay ${params}
}

### think action

describe_think() {
	echo "Show a pensive cow"
}

describe_think_parameters() {
  echo "<text>"
}

describe_think_options() {
  echo "text : Text to display"
  echo "--sheep : Use a sheep rather than a cow"
}

do_think() {
  local params=
  while [[ ${1#--} != ${1} ]] ; do
    if [[ "--sheep" == ${1} ]] ; then
      shift
      params="${params} -f sheep"
    elif [[ "--" == "${1}" ]] ; then
      break
    else
      die -q "Unknown parameter ${1}"
    fi
  done

  echo "${@:-Am I a cow?}" | cowthink ${params}
}

As you can see, the format is fairly similar to that of an ebuild -- it is a bash script which is run in a special environment. This is intentional. There are DESCRIPTION and VERSION variables globally which are used by eselect and some of the default action handlers, and a series of functions.

Unlike ebuilds, the function names are not fixed. Any function whose name starts with do_ is considered to be an action implementation. It is conventional to have a describe_ function for every do_ function that gives a short description of the function -- this is used for eselect modulename help, for example. The describe_actions_options and describe_action_parameters functions are optional.

Standard Action Names

The following list contains suggested allowed names for actions. If there is no suitable name on the list for your task, it is best to ask for the list to be updated -- for consistency, it would be nice to have a standardised list of action names. (The cow module, being a silly demonstration module, is exempt.)

• help - Display a help message. Automatic.
• usage - Display a usage message. Automatic.
• version - Display the current version. Automatic.
• show - Used to display the current provider of a symlink, or the currently installed module, or the current status.
• list - Used to display all available providers of a symlink, or all available modules.
• set - Used to set a new provider or a symlink.
• enable - Used to enable an optional feature.
• disable - Used to disable an optional feature.
• scan - Read information off the current filesystem.
• update - Used to automatically select a new provider for a symlink (as opposed to set, which generally takes a parameter manually selecting the provider) or to gather system information that is vital to further actions.

3.  Utility Functions

Introduction

eselect provides many utility functions. These are useful for standardised output formatting. Where possible, these should be used, especially for output. If a standard function is not available for the output format required, consider implementing one.

The following categories of function are available by default:

• General Utility Functions
• Output Utility Functions
• Manipulation Functions
• Path-Manipulation Functions
• Test Functions

To use any of the other functions, you have to first inherit the corresponding library file.

General Utility Functions

These are implemented in libs/core.bash.

The die Function

The die function (which, unlike its ebuild counterpart, can be called from within subshells) is used to exit with a fatal error. It should be invoked as die -q "Message to display". If the -q is not provided, a stacktrace will be displayed -- this should never happen because of user input error, only abnormal conditions.

The check_do Function

The check_do utility function checks that the first parameter is a function, and then calls it with any additional parameters as its arguments. If the function does not exist, die is called. Again, this is mostly internal.

The do_action Function

The do_action utility function is the correct way to call a utility function which is defined in another module. The first parameter is the action, additional parameters are passed as arguments.

The inherit Function

The inherit function sources eselect library files based on their name. In order to source the file libs/foo.bash you have to add inherit foo in global scope of your module.

Output Utility Functions

These are implemented in libs/output.bash

The write_error_msg Function

The write_error_msg function displays an error message in the standard format. It is similar to eerror.

The write_warning_msg Function

The write_warning_msg function displays a warning message in the standard format. It is similar to ewarn.

The write_list_ Function

To display a list, the write_list_ family of functions should be used. Lists should always start with a header, which can be displayed using write_list_start The Header.

To display a numbered list, the write_numbered_list_entry function should be used for each item. The first parameter is the list item number, the second is the list item text (remember to quote this).

To display a keyword/value list, the write_kv_list_entry function should be used. The first parameter is the key, the second the value.

The write_numbered_list function is a wrapper around write_numbered_list_entry that handles the numbering automatically. Each parameter passed is displayed as a numbered list item, the first with index 1, the second with index 2 and so on. If -p is passed as the first argument to these functions, plain highlighting is used.

The highlight Function

The highlight utility function can be used to emphasise some text which is to be displayed by any of the above functions. A typical invocation might look like the code listing shown below.

write_list_start "This is $(highlight list) example"
write_kv_list_entry "First" "This is the first"
write_kv_list_entry "$(highlight Second)" "This is the $(highlight second) entry"
write_kv_list_entry "Third" "$(highlight The end)"

The highlight_warning Function

The highlight_warning function is like highlight, but for warnings. It displays the text in question in red.

The space Function

The space utility function takes a single integer parameter. It displays that many space characters.

Test Functions

These are implemented in libs/tests.bash.

The has Function

The has utility function is like portage's hasq. It returns true if and only if the first parameter is equal to any of the remaining parameters.

The is_function Function

The is_function utility function returns true if and only if its parameter exists and is a function. This is mostly used internally, but may have some use for modules.

The is_number Function

Returns true if and only if the parameter is a positive whole number.

Path-Manipulation Functions

These are implemented in libs/path-manipulation.

The basename Function

The basename function is a transparent bash-only replacement for the external basename application.

The dirname Function

The dirname function is a transparent bash-only replacement for the external dirname application.

The canonicalise Function

The canonicalise function is a wrapper to either GNU readlink or realpath.

Manipulation Functions

These are implemented in libs/manip.bash.

The svn_date_to_version Function

The svn_date_to_version function can be used instead of manually keeping track of VERSION. It is safe to use in global scope. The canonical usage is as shown below.

SVN_DATE='$Date: 2006/03/31 11:37:23 $'
VERSION=$(svn_date_to_version "${SVN_DATE}" )
(Now turn on the SVN keyword expansion for the module)
svn propset svn:keywords "Date" modules/foo.eselect

Configuration Functions

These are implemented in libs/config.bash.

The store_config Function

The store_config function saves a key/value pair in a given configuration file which is passed as first argument. This file is a bash script consisting only of key/value pairs and should not be altered manually. Comments in the file will be deleted each time store_config is called. The function is invoked as store_config filename key value.

The load_config Function

The load_config function loads a stored value from the module's configuration file. It is invoked as load_config filename key and prints the associated value.

The append_config Function

The append_config function adds an item to an already stored value in themodules configuration file. It uses load_config/store_config internally and should be invoked as append_config filename key item. Note that the item will not be appended if it occurs in the key's value already.

Multilib Functions

These are implemented in libs/multilib.bash.

The list_libdirs Function

The list_libdirs function returns a set of valid libdirs for the used architecture. By default it uses /etc/ld.so.conf to obtain all the valid libdirs. If this fails due to a missing or broken file, this function uses uname to determine the architecture.

Portage Functions

These are implemented in libs/portage.bash.

The arch Function

The arch function returns the correct value of ${ARCH} for the current system. If Portage cannot provide this information, arch falls back to a uname -m and uname -s based lookup-table.

The portageq Function

The portageq function transparently wraps the corresponding Portage script whilst redirecting stderr to /dev/null.

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