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Wednesday, December 31, 2014

Regular Expressions in WLST

Python based WLST tutorial is to present a detailed and descriptive introduction into regular expressions. Every scripting language powered up with this regular expressions.


Regular expressions examples in WLST
Regular Expressions in WLST

In scripting, Very complex problems can be resolved with simple regular expressions. If you are not aware of each expressions meaning then it would be Greek &  Latin. You need to understand how they can be applicable then you can construct your WLST script in such a way that it could give a fantastic outcomes. A regular expression is that a set of possible input raw strings (includes alphanumerical, whitespaces, symbols).

Regular expressions descends from fundament concept in Computer Science called finite automata theory. A regular expression can match a string in more than one place.

Meta Characters in WLST

The special meaning for each symbol that we use in the regular expression. We have the following meta characters allowed in WLST.
WLST using meta chars

Dot . in expression – any char

The . dot or period regular expression can be used to matches any character. Remember this don’t matches new line ‘\n’.


The Character classes

Character classes [] can be used to match any specific set of characters.
Here is the example to understand the expression that uses character class. The expression second char can be one of the three chars given in the char class [eor]. So the pattern matches three words from the given text.

Negate character class

Character class can be negated with ^ symbol inside the character class. That is [^].
[aeiou] will match any of the characters a, e, i, o, or u
[yY]es will match Yes or yes
Negate Character class in re


Ranges can also be specified in character classes
[1-9] is the same as [123456789]
[abcde] is equivalent to [a-e]


You can also combine multiple ranges in the pattern
[abcde123456789] is equivalent to [a-e1-9]

Note that the hyphen - character has a special meaning in a character class but only if it is used within a range, if you use hypen at beginning its meaning changes it doesn't meant for range.
[-123] would match the characters -, 1, 2, or 3

Commonly used character classes can be referred to by name (alpha, lower, upper, alnum, digit, punct, cntrl)
Syntax [:name:]
[a-zA-Z]       [[:alpha:]]
[a-zA-Z0-9]    [[:alnum:]]
[45a-z]      [45[:lower:]]
Important for portability across languages
compile - search, match patterns on data 

Regular expression FLAGS


re.I == re.IGNORECASE Ignore case
re.L == re.LOCALE Make \w, \b, and \s locale dependent
re.M == re.MULTILINE Multiline
re.S == re.DOTALL Dot matches all (including newline)
re.U == re.UNICODE Make \w, \b, \d, and \s unicode dependent
re.X == re.VERBOSE Verbose (unescaped whitespace in pattern
is ignored, and '#' marks comment lines)

5 important re functions on WLST

There are few regular expression functions defined in the re module. Lets experiment with each one and see how they work.
wls:/offline> dir(re)
['DOTALL', 'I', 'IGNORECASE', 'L', 'LOCALE', 'M', 'MULTILINE', 'S', 'U', 'UNICODE', 'VERBOSE', 'X', '__all__', '__doc__', '__file__', '__name__', 'compile', 'error', 'escape', 'findall', 'match', 'module', 'name', 'purge', 'search', 'split', 'sre', 'sub', 'subn', 'sys', 'template']
The re module methods and their functionality

Lets begin here...

  1. The re.match() method
  2. The match() method works is that it will only find matches if they occur at the start of the string being searched.
    wls:/offline> import re
    wls:/offline> str="WLST WebLogic wsadmin WebSphere"
    wls:/offline> mo=re.match(r'WLST',str)
    wls:/offline> mo.group(0)
    'WLST'
    

  3. The re.split() method
  4. The re.split() method accepts a pattern argument. This pattern specifies the delimiter. With it, we can use any text that matches a pattern as the delimiter to separate text data. This is powerful.
    clstrAddress="machine01.vybhava.com:8901,machine02.vybhava.com:8902"
    wls:/offline>  s=re.split(r"[:,]\d{4}",clstrAddress)
    wls:/offline> s
    ['machine01.vybhava.com', ',machine02.vybhava.com', '']
    

  5. The re.search() function in re
  6. The following examples will illustrate how to search function with re module flags without it.
    #=====================================================================
    # Created by : Manish K
    # Updated by : Pavan Devarakonda
    # Date : 20 Dec 2014
    #=====================================================================
    import re
    
    s1 = "India is a country!"
    s2 = "Delhi is the capital of India"
    str = s1 + "\n" + s2
    
    ###### To Search first char in multilne
    mo = re.search(r"^D[\w]*", str, re.M)
    print "searched word with first char D:",mo.group()
    
    ###### To Search last char in multilne
    
    mo1 = re.search(r"I[\w]*$", str, re.M)
    print "Searched India:", mo1.group()
    
    ##### To match ignoring case
    
    mo2 = re.search(r"india", str, re.I)
    print "Ignore case:", mo2.group()
    
    if re.search(r'[!@#$%^&*()]', str):
     print "Some special Char found"
    else:
     print "Nothing special found"
    
    print "Original str:", str
    splitstr = re.split("\n", str)
    print "split string with newline:",splitstr
    
    ## Optional Items
    optSearch = "Find date Feb 2015, 12"
    mo3 = re.search(r"Feb(ruary)? 2015", optSearch)
    print "Optional search:", mo3.group()
    
    ## using +
    mo4 = re.search(r"(Feb(ruary)?) ([0-9]+)", optSearch)
    print "Search with + : ", mo4.group()
    
    
    ## unsing *
    mo5 = re.search(r"[0-9].*", optSearch)
    print "Using *", mo5.group()
    
    ### Grouping by the use of ()
    
    gprStr = "Customer number: 232454, Date: February 12, 2015"
    mo6 = re.search("([0-9]+).*: (.*)", gprStr)
    print "Grouping with ():"
    print mo6.group()
    print mo6.group(1)
    print mo6.group(2)
    print mo6.groups()
    
    
    Lets execute the above experiment on search function.
    $ wlst search_re.py
    
    Initializing WebLogic Scripting Tool (WLST) ...
    
    Welcome to WebLogic Server Administration Scripting Shell
    
    Type help() for help on available commands
    
    searched word with first char D: Delhi
    Searched India: India
    Ignore case: India
    Some special Char found
    Original str: India is a country!
    Delhi is the capital of India
    split string with newline: ['India is a country!', 'Delhi is the capital of India']
    Optional search: Feb 2015
    Search with + :  Feb 2015
    Using * 2015, 12
    Grouping with ():
    232454, Date: February 12, 2015
    232454
    February 12, 2015
    ('232454', 'February 12, 2015')
    
    

  7. The re.findall() function

  8. When there is the need to find the multiple occurrences of a pattern in a text then findall() is the best function to use. This function returns a list of resulted strings.

    Example on findall method in re module.
    import re
    line="WebLogic Automation course helps WebLogic Admins fish best opportunities"
    
    print "words starts with A"
    print re.findall(r"\bA[\w]*",line)
    
    print "Find all five characthers long words"
    print re.findall(r"\b\w{5}\b", line)
    
    # Find all four, six characthers long words
    print "4, 6 char long words"
    print re.findall(r"\b\w{4,6}\b", line)
    
    # Find all words which are at least 13 characters long
    print "13 char"
    print re.findall(r"\b\w{13,}\b", line)
    
    Execution of the above example gives the output as follows:
    $ wlst findallre.py
    
    Initializing WebLogic Scripting Tool (WLST) ...
    
    Welcome to WebLogic Server Administration Scripting Shell
    
    Type help() for help on available commands
    
    words starts with A
    ['Automation', 'Admins']
    Find all five characthers long words
    ['helps']
    4, 6 char long words
    ['course', 'helps', 'Admins', 'fish', 'best']
    13 char
    ['opportunities']
    
    

  9. The re.sub() function

  10. One of the most important function in the re module is sub(). It works like 'find and replace'.
    
    sub(pattern, repl, string [, count=0])
    
    

    This method replaces all occurrences of the re pattern in the given string with repl, substituting all occurrences unless max count provided. This method would return modified string as output.
    #!/usr/bin/python
    import re
    
    DOB = "28-11-2003# This is DOB "
    
    # Delete Python-style comments
    num = re.sub(r'#.*$', "", DOB)
    print "DOB Num : ", num
    
    # Remove anything other than digits
    x = re.sub(r'\D', "", DOB)
    print "DOB without - : ", x
    
    # Substituting other symbol in anything other than digits
    FDOB = re.sub(r'\D', "/", num)
    print "DOB in new format : ", FDOB
    
    This find and replacement experiment output
    DOB Num :  28-11-2003
    DOB without - :  28112003
    DOB in new format :  28/11/2003
    

    Hope this has given you some basic idea on re module usage in WLST shell. This can help you when you write monitoring script and that will be given to report or graph designs on UI.
Write back to us with your Feedback, queries on regular expressions usage in WLST.

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