The ‘xdgdirs’ Manual

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The ‘xdgdirs’ Manual

This manual documents xdgdirs 2.2.

Copyright © 2013, 2015 Thien-Thi Nguyen

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the appendix entitled “GNU Free Documentation License”.


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1 Introduction

xdgdirs’ is a program that displays the names and values of the six XDG_* env vars related to the XDG Basedir Specification, formatted as a Scheme- and Lisp-friendly alist, or optionally as an associative array in the literal data syntax of various languages.

Other programs can invoke ‘xdgdirs’ to obtain the required data in one shot, avoiding the need to implement the (admittedly simple, but anyway fiddly1 and memory consuming) algorithms involved.

There are four (or three, depending on language) data types represented in the output: symbols, strings, list of strings, and the number 0. For Scheme and Lisp, the name is a symbol; for the other languages, it is a string. Also, “list of strings” can be read as “array of strings” or “sequence of strings” in other languages. Here is a table:

env varnamevalue type
XDG_DATA_HOMEdata-homestring
XDG_CONFIG_HOMEconfig-homestring
XDG_DATA_DIRSdata-dirslist of strings
XDG_CONFIG_DIRSconfig-dirslist of strings
XDG_CACHE_HOMEcache-homestring
XDG_RUNTIME_DIRruntime-dirstring

The number 0 indicates “not available”, possible for any of the six values, especially when given the ‘--no-defaults’ option. For example, here is a simple invocation on the author’s computer, where there are no XDG_* env vars set:

$ xdgdirs
((data-home . "/home/ttn/.local/share")
 (config-home . "/home/ttn/.config")
 (data-dirs "/usr/local/share" "/usr/share")
 (config-dirs "/etc/xdg")
 (cache-home . "/home/ttn/.cache")
 (runtime-dir . 0))

The output here has been reformatted to be more human readable; the actual output appears on one line. Note that runtime-dir has no default value and thus is “not available”. Here is a more complicated invocation:

$ xdgdirs cool –lang json
{
  "data-home" : "/home/ttn/.local/share/cool",
  "config-home" : "/home/ttn/.config/cool",
  "data-dirs" : ["/usr/local/share/cool", "/usr/share/cool"],
  "config-dirs" : ["/etc/xdg/cool"],
  "cache-home" : "/home/ttn/.cache/cool",
  "runtime-dir" : 0
}

(This output is reproduced exactly.) See Invoking xdgdirs, for details.


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2 Invoking xdgdirs

In addition to the usual ‘--help’ and ‘--version’ invocations, usage is straightforward:

xdgdirs [package] [options]

If package is specified, it is appended to all the (directory) strings, separated from its parent directory by ‘/’ (slash). Options are:

--sequence
-s

Instead of displaying all the variables as a single data structure (alist or associative array), display the name/value pairs, each on a line of its own, without intervening syntax, e.g., ‘,’ (comma). For example:

$ xdgdirs –sequence
(data-home . "/home/ttn/.local/share")
(config-home . "/home/ttn/.config")
(data-dirs "/usr/local/share" "/usr/share")
(config-dirs "/etc/xdg")
(cache-home . "/home/ttn/.cache")
(runtime-dir . 0)
--no-defaults
-D

The specification provides for default values in the case where an XDG_foo env var is not set (or empty). This option inhibits those values so that the value is 0 (not available). For example:

$ xdgdirs –no-defaults
((data-home . 0)
 (config-home . 0)
 (data-dirs . 0)
 (config-dirs . 0)
 (cache-home . 0)
 (runtime-dir . 0))
--lang lang
-l lang

This option specifies that output should be in the syntax of lang, one of:

sexp

Each pair has one the forms:

(symbol . 0)
(symbol . string)
(symbol string …)

The aggregate is a classic alist. This is the default if ‘--lang’ is unspecified.

json

Each pair has one of the forms:

string : 0
string : string
string : [ string, … ]

Pairs are separated by ‘,’ (comma) and the aggregate surrounded by ‘{’ and ‘}’ (curly braces).

bash

Each pair has one of the forms:

[symbol]=0
[symbol]="dir"
[symbol]="dir:…"

The aggregate is surrounded by ‘(’ and ‘)’ (parens).

perl

Each pair has one of the forms:

string => 0
string => string
string => [ string, … ]

Pairs are separated by ‘,’ (comma) and the aggregate surrounded by ‘(’ and ‘)’ (parens).

lua

Each pair has one of the forms:

[string] = 0
[string] = string
[string] = { string, … }

Pairs are separated by ‘,’ (comma) and the aggregate surrounded by ‘{’ and ‘}’ (curly braces).

yaml

Each pair has one of the forms:

symbol: 0
symbol: string
symbol: [ string, … ]

For ‘--lang yaml’, option –sequence has no effect; The output is a top-level (unindented) mapping.

For any other lang, ‘xdgdirs’ displays to stderr “unrecognized lang” and exits failurefully.

If all goes well, after displaying the output, ‘xdgdirs’ exits successfully.


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3 Dependencies

There are three kinds of dependencies: operational, data and community.

3.1 operational

First the operational dependency: ‘xdgdirs’ is a Guile Scheme script, so it needs Guile (any version) to run. Normally, it uses the first guile executable found in the PATH env var. You can use env var GUILE to override this. For instance:

GUILE=$HOME/experimental/guile-42 xdgdirs …

If no Guile is available, the shell will probably complain loudly.

3.2 data

Now for the data dependency: Obviously, the whole point of ‘xdgdirs’ is to look at certain XDG_* env vars (see list). Additionally, in the case of unspecified XDG_* env vars many of the default values ‘xdgdirs’ must ascertain are “user-specific” and involve the user’s “home directory”. ‘xdgdirs’ computes this as follows:

  1. If HOME is useful, use it.
  2. Otherwise, try to find the appropriate pwent:
    1. via login
      1. If LOGNAME is useful, use it.
      2. Otherwise, if USER is useful, use it.
    2. via uid

Here, useful means the env var is set and has a non-empty value. If the user’s home directory cannot be determined, ‘xdgdirs’ displays to stderr a diagnostic to that effect and exits failurefully.

3.3 community

Lastly, the community dependency: The aim of ‘xdgdirs’ is to serve a wide community of programmers, beyond those who happen to prefer its implementation language and default output syntax. Its long-term viability depends on feedback: bug-reports, (occasional) feature requests, and plain old word-of-mouth advertizing. So, do be heard — spread the word!


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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
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    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

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  6. COMBINING DOCUMENTS

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  7. COLLECTIONS OF DOCUMENTS

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To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

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Index

Jump to:   -   0  
B   C   D   I   J   L   N   P   S   T   U   X   Y   Z  
Index Entry  Section

-
--lang’, command-line option: Invoking xdgdirs
--no-defaults’, command-line option: Invoking xdgdirs
--sequence’, command-line option: Invoking xdgdirs

0
0 (zero): Introduction

B
bash: Invoking xdgdirs

C
command-line option ‘--lang: Invoking xdgdirs
command-line option ‘--no-defaults: Invoking xdgdirs
command-line option ‘--sequence: Invoking xdgdirs
command-line options: Invoking xdgdirs
community dependency: Dependencies

D
data dependency: Dependencies
dependency operational: Dependencies
dependency, community: Dependencies
dependency, data: Dependencies
dependency, operational: Dependencies

I
intended client: Introduction
invocation: Invoking xdgdirs

J
json: Invoking xdgdirs

L
lua: Invoking xdgdirs

N
not available: Introduction

P
perl: Invoking xdgdirs

S
sexp: Invoking xdgdirs

T
types: Introduction

U
usage: Invoking xdgdirs

X
XDG Basedir Specification: Introduction

Y
yaml: Invoking xdgdirs

Z
zero (0): Introduction

Jump to:   -   0  
B   C   D   I   J   L   N   P   S   T   U   X   Y   Z  

Footnotes

(1)

whitespace trimming, trailing ‘/’ (slash) removal, empty value normalization, and so on