Ruby: configuration file parsing utility
Posted 04-18-2011 at 10:12 AM by catkin
Tags configuration, file, parse, parsing, ruby
Netsearching found three options for Ruby to parse configuration files:
The code generates detailed error messages if the config file is defective -- useful when creating config files.
It may be easier to understand the code when its functionality is clear so here is a commented sample configuration file:
When programming, the first thing to do is to provide a complete set of default parameters:
If a config file is to be parsed (this example assumes it can only be named on the command line):
The ParseConfigFile object receives a list of keys for validation and checks for empty values; more specific error trapping is left for the caller allowing ParseConfigFile to be a library utility:
The nitty-gritty of parsing is done by the GetConfigFileData object, called once for each configuration element:
For completeness, here is a simple example of error traps done after parsing the config file:
- YAML is powerful but I felt the the configuration file format was too complex for end-users. YAML example.
- drks' ParseConfig was not powerful enough for my needs.
- Hans' parse_config was also not powerful enough for my needs.
The code generates detailed error messages if the config file is defective -- useful when creating config files.
It may be easier to understand the code when its functionality is clear so here is a commented sample configuration file:
Code:
# * Leading and trailing whitespace is discarded.
# * Lines beginning with # and empty lines are ignored.
# * Lines ending in \ are continuation lines. The \ is removed and the contents
# of the following line appended (any whitespace before the \ is retained).
# * For string values:
# - What is left must be of the format keyword = value
# - Whitespace after the keyword is discarded.
# - Whitespace before the value is discarded.
# * For array values:
# - What is left must be of the format keyword = [
# - Followed by none or more lines, each one being an array member string
# These lines may be continued using a trailing \
# - Followed by a line containing a single ]
# * For hash values:
# - What is left must be of the format keyword = {
# - Followed by none or more lines, each one being a hash key and value like
# my_key => my_value
# These lines may be continued using a trailing \
# - Followed by a line containing a single }
CollationRootDir = /srv/docoll_dev/
Database = {
host => localhost
db_name => docoll_dev
password => some_password
port => 5432
user => superuser
}
# LeadingDirsToStrip regexes in config files are case-insentive
LeadingDirsToStrip = [
/srv/hardcopy_indexes/
/srv/old_KT/
/srv/rsync/[^/]*/
^home/[^/]*/
^[A-Z]/
.*/All Users/Documents/
.*/My Documents/
.*/My Music/
.*/My Pictures/
]
Code:
def InitialiseParameters
$parameters = Hash.new
# In alphabetical order ...
$parameters[ "ConfigFile" ] = ""
$parameters[ "CollationRootDir" ] = "/srv/docs/"
$parameters[ "LeadingDirsToStrip" ] = [ \
%r|/srv/rsync/| \
]
$parameters[ "Database" ] = { \
:db_name => "collation",
:host => "localhost",
:password => "whatever",
:port => 5432,
:user => "superuser"
}
$parameters[ "SourceRootDirs" ] = [ "/srv/rsync/" ]
end
Code:
# Parse any config file
# Must do now so config file settings can be over-ridden by the command line
x = ARGV.index( "--config" )
if x != nil && ARGV[ x + 1 ] != nil
config_file_error_msg = ParseConfigFile( ARGV[ x + 1 ], $parameters.keys )
else
config_file_error_msg = ''
end
Code:
def ParseConfigFile( config_path, *valid_keywords )
# TODO: change from valid_keywords to desired_keywords?
# TODO: nice to pass name of variable to load with config data rather than assuming $parameters
# TODO: support "=" in value
begin
fd = File.open( config_path, 'r' )
rescue => error_info
return "\n Config file: #{ error_info }"
end
error_msg = ""
while true
key, value, get_error_msg = GetConfigFileData( fd )
if get_error_msg == ''
if key == ""; break end
# Validate key
valid = false
valid_keywords[ 0 ].each \
do |valid_keyword|
if key == valid_keyword; valid = true; break; end
end
if valid
$parameters[ key ] = value
else
error_msg += "\n Invalid keyword '#{ key }' on line number #{ $INPUT_LINE_NUMBER }"
end
# Validate value
if value == ""
error_msg += "\n No value on line number #{ $INPUT_LINE_NUMBER }"
end
else
error_msg += get_error_msg
break
end
end
if error_msg != ''
error_msg = "Configuration file (#{ config_path }) error(s):" + error_msg
end
fd.close
return error_msg
end
Code:
def GetConfigFileData( fd )
# TODO: don't treat # in quoted values as a comment
# TODO: allow comments after data
continuing = false
data = ''
getting_array = false
getting_hash = false
key = ''
begin
while (line = fd.readline)
line.strip!
# Ignore comments and empty lines
if line.index( '#' ) != nil || line == ''; next end
# Gather key and value
data += line
case data[ -1 ]
when "\\"
continuing = true
data.slice!( -1, 1 )
data.rstrip!
next
when "["
if getting_array
return nil, nil, \
"\n New array started before end of array started on line" \
+ array_start_line
end
if getting_hash
return nil, nil, \
"\n Array started before end of hash started on line" \
+ hash_start_line
end
data.slice!( -1, 1 )
data.rstrip!
array_start_line = "#{ $INPUT_LINE_NUMBER }"
if data[ -1 ] != "="
return nil, nil, \
"\n Array start line not of format 'key = [' on line " \
+ array_start_line
end
getting_array = true
array = Array.new
when "]"
if ! getting_array
return nil, nil, \
+ "\n Array end on line #{ $INPUT_LINE_NUMBER } before array started"
end
data.slice!( -1, 1 ).rstrip!
if data != ''
return nil, nil, \
+ "\n Data invalidly given before ] on line #{ $INPUT_LINE_NUMBER }"
end
return key, array, ""
when "{"
if getting_array
return nil, nil, \
"\n Hash started before end of array started on line" \
+ array_start_line
end
if getting_hash
return nil, nil, \
"\n New hash started before end of hash started on line" \
+ hash_start_line
end
data.slice!( -1, 1 )
data.rstrip!
hash_start_line = "#{ $INPUT_LINE_NUMBER }"
if data[ -1 ] != "="
return nil, nil, \
"\n Hash start line not of format 'key = {' on line " \
+ hash_start_line
end
getting_hash = true
hash = Hash.new
when "}"
if ! getting_hash
return nil, nil, \
"\n Hash end on line #{ $INPUT_LINE_NUMBER } before hash started"
end
data.slice!( -1, 1 ).rstrip!
if data != ''
return nil, nil, \
"\n Data invalidly given before } on line #{ $INPUT_LINE_NUMBER }"
end
return key, hash, ""
end
if key == ''
if ! data.include?( '=' )
return nil, nil, "\n No = in #{ data }"
end
key, data, rest = data.split( '=' )
if rest != nil
return nil, nil, "\n '=' not supported in value (" + data + rest + ')'
end
key.rstrip!
if data == nil
data = ""
else
data.lstrip!
end
end
if data != nil && data != ''
if getting_array
array += [ data ]
data = ""
elsif getting_hash
# TODO: would be nice to accept "key: value" too
if ! data.include?( " => " )
return nil, nil, \
+ "\n Hash key/value on line #{ $INPUT_LINE_NUMBER } does not have ' => '"
end
hash_key, hash_value = data.split( " => " )
hash = hash.merge!( { hash_key.rstrip => hash_value.lstrip } )
data = ""
else
return key, data, ""
end
end
end
rescue EOFError
if continuing
error_msg += "\n End of file found when continuation line expected"
end
if getting_array
error_msg += "\n End of file found before end of array started on line" \
+ array_start_line
end
if getting_hash
error_msg += "\n End of file found before end of hash started on line" \
+ hash_start_line
end
return "", "", ""
end
end
Code:
def CheckParameters( )
error_msg = ''
error_msg += CheckDir( $parameters[ "CollationRootDir" ], 'w' )
$parameters[ "SourceRootDirs" ].each \
do |source_dir|
error_msg += CheckDir( source_dir, 'r' )
end
return error_msg
end
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