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14. Regular expressions

14. REGULAR EXPRESSIONS


Massuser supports reguar expressions for the homedirectory attribute and for the apple/posix homedirectory.

14.1. Regular expression overview.

Regular Expressions are a widely-used method of specifying patterns of text to search for. Special metacharacters allow You to specify, for instance, that a particular string You are looking for occurs at the beginning or end of a line, or contains n recurrences of a certain character.
Regular expressions look ugly for novices, but really they are very simple (well, usually simple ;) ), handly and powerfull tool.
Simple matches
Any single character matches itself, unless it is a metacharacter with a special meaning described below.
A series of characters matches that series of characters in the target string, so the pattern "bluh" would match "bluh'' in the target string. Quite simple, eh ?
You can cause characters that normally function as metacharacters or escape sequences to be interpreted literally by 'escaping' them by preceding them with a backslash "\", for instance: metacharacter "^" match beginning of string, but "\^" match character "^", "\\" match "\" and so on.
Examples:
foobar matchs string 'foobar'
\^FooBarPtr matchs '^FooBarPtr'
Escape sequences
Characters may be specified using a escape sequences syntax much like that used in C and Perl: "\n'' matches a newline, "\t'' a tab, etc. More generally, \xnn, where nn is a string of hexadecimal digits, matches the character whose ASCII value is nn. If You need wide (Unicode) character code, You can use '\x{nnnn}', where 'nnnn' - one or more hexadecimal digits.
\xnn char with hex code nn
\x{nnnn} char with hex code nnnn (one byte for plain text and two bytes for Unicode)
\t tab (HT/TAB), same as \x09
\n newline (NL), same as \x0a
\r car.return (CR), same as \x0d
\f form feed (FF), same as \x0c
\a alarm (bell) (BEL), same as \x07
\e escape (ESC), same as \x1b
Examples:
foo\x20bar matchs 'foo bar' (note space in the middle)
\tfoobar matchs 'foobar' predefined by tab
Character classes
You can specify a character class, by enclosing a list of characters in [], which will match any one character from the list.
If the first character after the "['' is "^'', the class matches any character not in the list.
Examples:
foob[aeiou]r finds strings 'foobar', 'foober' etc. but not 'foobbr', 'foobcr' etc.
foob[^aeiou]r find strings 'foobbr', 'foobcr' etc. but not 'foobar', 'foober' etc.
Within a list, the "-'' character is used to specify a range, so that a-z represents all characters between "a'' and "z'', inclusive.
If You want "-'' itself to be a member of a class, put it at the start or end of the list, or escape it with a backslash. If You want ']' you may place it at the start of list or escape it with a backslash.
Examples:
[-az] matchs 'a', 'z' and '-'
[az-] matchs 'a', 'z' and '-'
[a\-z] matchs 'a', 'z' and '-'
[a-z] matchs all twenty six small characters from 'a' to 'z'
[\n-\x0D] matchs any of #10,#11,#12,#13.
[\d-t] matchs any digit, '-' or 't'.
[]-a] matchs any char from ']'..'a'.
Metacharacters
Metacharacters are special characters which are the essence of Regular Expressions. There are different types of metacharacters, described below.
Metacharacters - line separators
^ start of line
$ end of line
\A start of text
\Z end of text
. any character in line
Examples:
^foobar matchs string 'foobar' only if it's at the beginning of line
foobar$ matchs string 'foobar' only if it's at the end of line
^foobar$ matchs string 'foobar' only if it's the only string in line
foob.r matchs strings like 'foobar', 'foobbr', 'foob1r' and so on
Metacharacters - predefined classes
\w an alphanumeric character (including "_")
\W a nonalphanumeric
\d a numeric character
\D a non-numeric
\s any space (same as [ \t\n\r\f])
\S a non space
You may use \w, \d and \s within custom character classes.
Examples:
foob\dr matchs strings like 'foob1r', ''foob6r' and so on but not 'foobar',
'foobbr' and so on
foob[\w\s]r matchs strings like 'foobar', 'foob r', 'foobbr' and so on but not 'foob1r',
'foob=r' and so on
Metacharacters - word boundaries
\b Match a word boundary
\B Match a non-(word boundary)
A word boundary (\b) is a spot between two characters that has a \w on one side of it and a \W on the other side of it (in either order), counting the imaginary characters off the beginning and end of the string as matching a \W.
Metacharacters - iterators
Any item of a regular expression may be followed by another type of metacharacters - iterators. Using this metacharacters You can specify number of occurences of previous character, metacharacter or subexpression.
* zero or more ("greedy"), similar to {0,}
+ one or more ("greedy"), similar to {1,}
? zero or one ("greedy"), similar to {0,1}
{n} exactly n times ("greedy")
{n,} at least n times ("greedy")
{n,m} at least n but not more than m times ("greedy")
*? zero or more ("non-greedy"), similar to {0,}?
+? one or more ("non-greedy"), similar to {1,}?
?? zero or one ("non-greedy"), similar to {0,1}?
{n}? exactly n times ("non-greedy")
{n,}? at least n times ("non-greedy")
{n,m}? at least n but not more than m times ("non-greedy")
So, digits in curly brackets of the form {n,m}, specify the minimum number of times to match the item n and the maximum m. The form {n} is equivalent to {n,n} and matches exactly n times. The form {n,} matches n or more times. There is no limit to the size of n or m, but large numbers will chew up more memory and slow down r.e. execution.
If a curly bracket occurs in any other context, it is treated as a regular character.
Examples:
foob.*r matchs strings like 'foobar', 'foobalkjdflkj9r' and 'foobr'
foob.+r matchs strings like 'foobar', 'foobalkjdflkj9r' but not 'foobr'
foob.?r matchs strings like 'foobar', 'foobbr' and 'foobr' but not 'foobalkj9r'
fooba{2}r matchs the string 'foobaar'
fooba{2,}r matchs strings like 'foobaar', 'foobaaar', 'foobaaaar' etc.
fooba{2,3}r matchs strings like 'foobaar', or 'foobaaar' but not 'foobaaaar'
A little explanation about "greediness". "Greedy" takes as many as possible, "non-greedy" takes as few as possible. For example, 'b+' and 'b*' applied to string 'abbbbc' return 'bbbb', 'b+?' returns 'b', 'b*?' returns empty string, 'b{2,3}?' returns 'bb', 'b{2,3}' returns 'bbb'.
You can switch all iterators into "non-greedy" mode (see the modifier /g).
Metacharacters - alternatives
You can specify a series of alternatives for a pattern using "|'' to separate them, so that fee|fie|foe will match any of "fee'', "fie'', or "foe'' in the target string (as would f(e|i|o)e). The first alternative includes everything from the last pattern delimiter ("('', "['', or the beginning of the pattern) up to the first "|'', and the last alternative contains everything from the last "|'' to the next pattern delimiter. For this reason, it's common practice to include alternatives in parentheses, to minimize confusion about where they start and end.
Alternatives are tried from left to right, so the first alternative found for which the entire expression matches, is the one that is chosen. This means that alternatives are not necessarily greedy. For example: when matching foo|foot against "barefoot'', only the "foo'' part will match, as that is the first alternative tried, and it successfully matches the target string. (This might not seem important, but it is important when you are capturing matched text using parentheses.)
Also remember that "|'' is interpreted as a literal within square brackets, so if You write [fee|fie|foe] You're really only matching [feio|].
Examples:
foo(bar|foo) matchs strings 'foobar' or 'foofoo'.
Metacharacters - subexpressions
Subexpressions are numbered based on the left to right order of their opening parenthesis.
First subexpression has number '1'
Examples:
(foobar){8,10} matchs strings which contain 8, 9 or 10 instances of the 'foobar'
foob([0-9]|a+)r matchs 'foob0r', 'foob1r' , 'foobar', 'foobaar', 'foobaar' etc.

Metacharacters - backreferences
Metacharacters \1 through \9 are interpreted as backreferences. \<n> matches previously matched subexpression #<n>.
Examples:
(.)\1+ matchs 'aaaa' and 'cc'.
(.+)\1+ also match 'abab' and '123123'
(['"]?)(\d+)\1 matchs '"13" (in double quotes), or '4' (in single quotes) or 77 (without quotes) etc
Perl extensions
(?imsxr-imsxr)
You may use it into r.e. for modifying modifiers by the fly. If this construction inlined into subexpression, then it effects only into this subexpression
Examples:
(?i)Saint-Petersburg matchs 'Saint-petersburg' and 'Saint-Petersburg'
(?i)Saint-(?-i)Petersburg matchs 'Saint-Petersburg' but not 'Saint-petersburg'
(?i)(Saint-)?Petersburg matchs 'Saint-petersburg' and 'saint-petersburg'
((?i)Saint-)?Petersburg matchs 'saint-Petersburg', but not 'saint-petersburg'
(?#text)
A comment, the text is ignored. Note that TRegExpr closes the comment as soon as it sees a ")", so there is no way to put a literal ")" in the comment.
This documentation is based on the helpfile of TRegExpr module created by:
Andrey V. Sorokin
Saint Petersburg, Russia
This e-mail address is being protected from spambots. You need JavaScript enabled to view it , This e-mail address is being protected from spambots. You need JavaScript enabled to view it
http://RegExpStudio.com (http://anso.da.ru)

14.2. Samples regular expression.

14.2.1. Sample 1

Suppose you have an organisation with 5 offices, and every office has it's own server. The eDirector has the following structure:

O=mobile
OU=DV (is the office in Deventer)
OU=ZW ..(office in Zwolle)
OU=... etc.
and under every office container there are department containers and in the department containers there are users (and no sub-containers). So a typical user would be booj.sales.dv.mobile
The servers are called fs-<office>-01 so FS-DV-01 in Deventer and FS-ZW-01 in Zwolle. All user homedirectories are in the root of the volume USR.
Options for creating user accounts for the different locations:

- set up 5 different set-files and do a seperate run for every office.
- create a mapping file with 5 context mappings
- create one regular expression rule.

Image

On the general tab of the reg-expression tab check the add context
On the netware tab give:

Image

 

Image


The ^ for start of string, The first (.*) will give the $1 = username, the first [.] marks the end of the username. Then the .*[.] stands for the department, not important here so there are no () around them. Then the (.*) will give the $2 = office value and the [.] marks the end of the office name.
In the template the $2 will be replace with the office name and the $1 with the user name.

14.2.2. Sample 2


Same situation, but not the could be a sub context under the department. (this expression works also for the previous situation.
Image
booj.grp1.sales.dv.hbw will give \\fs-dv-01\usr\booj and leek.sales.zw.hbw will give \\fs-zw-01\usr\leek.
Make sure you start at the start so ^
(.*?)[.] This will give the $1 because of the () then .*? any character until first condition (non greedy) and the [.] is the first dot in the string. In the samples $1will become booj and leek.
Then .* will read any character greedy (as many as possible) until the next condition. The next condition is given by [.](.*)[.] the last [.] will be the last dot in the string (between office and mobile here) then (.*) will fill the $2 and the first [.] will stop the copy of chars to $2 at the first dot left of the officename.
So now there can be any number of containers between the username and office container.

14.2.3. Sample 3

Suppose you have the following situation on a primairy school

cn=username and uniqueID is the username_grade where grade is the k, 01..12..
Depending on the context of the user object you want to map the fileservername.
You want to map the volumename based upon the grade, where the volumename will be home1<grade>, except for k (kindergarden) you want home100. The user directory will be in the root of the volume.
The tree would be.
O=schoolname
ou=building1 and all users for that building are in this container
ou=buiding2
Select uiqueID as the attribute on the general tab of the regular expression and check add context.
For this you need two expressions:
Image
One for the _k and one for the rest.
With regular expressions allmost anything can be done

In a future version of the program there will also be support for userquota's and directory limits based upon regular expressions.

14.3. Extention of regular expressions

You can add the functions/attribute substitution to the template string. The program will evaluate the result of the expression and supply the extra mapping/substitution. See also "extra options path definitions"