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Extract a string from file

Posted on 2012-12-24
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Last Modified: 2012-12-26
I need some pointers / example of a powershell script that will extract a string from a file based on the starting position of that string.

Appreciate the feedback.
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Question by:codedigger
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12 Comments
 
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Expert Comment

by:Subsun
ID: 38719402
You can use Select-String, for example following command will retrieve the lines strting with subsun from file test.txt
gc c:\test.txt | Select-String -Pattern "^subsun"
More for more examples you can refer the following articles. If you have any specific requirement then you can ask, so we can provide you the exact command to retrieve the required string..

References :
http://technet.microsoft.com/en-us/library/hh849903.aspx
http://www.computerperformance.co.uk/powershell/powershell_select_string.htm
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Author Comment

by:codedigger
ID: 38719405
Following "Pattern"s is fairly straightforward, my problem is, I don't have a pattern in the file, I however know the starting and endining position of the string I'm after and extracting it that way ensures accuracy.
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Expert Comment

by:Dale Harris
ID: 38719411
You can try the "substring" command:

$Test = "Hello World"
$Test.substring(0,5)
Output: Hello

Or you can do a split based on characters like space or hyphen

$Test.split(" ")[0]
Output: Hello
$NewTest = $Test.split(" ")
$NewTest.count
Output:2
$NewTest
Output:
Hello
World

HTH,

DH
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LVL 40

Expert Comment

by:Subsun
ID: 38719427
If you want to extract based on the string position, then you can try to retrieve the line based on index and again use substring to get exact string value....

From following sample text file..
Subsun Test EE
Subsun Testing EE
Subsun EE Testing

Open in new window


Following command will return Testing from line 2
(gc test.txt | Select-Object -Index 1).substring(7,7)
Following command will return EE from line 3
(gc test.txt | Select-Object -Index 2).substring(7,2)

Not sure if this is what you are looking for..
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Author Comment

by:codedigger
ID: 38719435
We're getting close and I'll try your suggestion, the file I have in mind has only one line and it's around 400 characters, and I'm only interested in extracting any value between position 29 and position 40, sometimes the value between these two positions could be 5 digits (that's for older customers), and sometimes it could be 8,9, 10 digits (for newer customers), so as long as I can get the value (whatever it is) between position 29 and 40 I'm happy.

Thx
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Expert Comment

by:Subsun
ID: 38719438
For single line file, you don't have to add index..
(gc test.txt).substring(28,11) should retrieve the characters from 29 to 40..
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Author Comment

by:codedigger
ID: 38719451
Thank you Subsun, I think your suggestion will work, but I just examined one of the files I'm dealing with and found that the spaces between delimiters collapses in based on the number of characters, so if I was to use the solution you recommended, the optimal way would be to begin at position 29 but end at the delimiter, in my case it is a comma "," this way if my customer ID is 5 digits and it begins at positon 29, I'd only need to grab whatever between position 29 and 34 and since the customer ID varies the only way to ensure that I'm only getting the cusomter ID is to grab whatever value between position 29 and the next delimiter.  sorry I didn't explain it this way earlier.
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Expert Comment

by:Dale Harris
ID: 38719483
Here's a solution I made a while back that does exactly what you're asking provided the line is always the same except for the customer ID

Using Subsun's previous information:

#We will first need to set the length of the whole string without the customer ID
$NormalLength = 142
#Then we get the length of the actual string
$Length = (gc test.txt).length
#Then we are going to do some simple math to figure out how large the customer ID is

#It's expressed like this: CustomerID Length = Length of string - Normal Length
$CustomerIDLength = $Length - $NormalLength

#Putting it all together in one line:

$CustomerID = (gc test.txt).substring(28,$((gc test.txt).length - 142))

or if you wanted to get the position 29, then split by "," (comma), then grab from the 29th position to the first comma, you could do something like this:

$CustomerID = ((gc test.txt).substring(28, 30)).split(",")[0]

I used 30 arbitrarily saying "the customer ID will never be longer than 30 characters".  You can change this accordingly.

Good luck!

-Dale
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Author Comment

by:codedigger
ID: 38719486
I'm getting this error now.

Method invocation failed because [System.Object[]] doesn't contain a method named 'substring'
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Expert Comment

by:Dale Harris
ID: 38719498
Try adding a .tostring() in between your .substring and the closing parentheses.
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Accepted Solution

by:
Subsun earned 500 total points
ID: 38719674
Try
((gc test.txt).substring(28)).split(",")[0]


For example..
PS C:\> gc test.txt # To see the content of file
ABCD EDFGHHIJKLMNABCD EDFGH START XXXXXXXXX XXXXXXXXXXXX XXX END ,NNN,NN,NN,NN
PS C:\> ((gc test.txt).substring(28)).split(",")[0]
START XXXXXXXXX XXXXXXXXXXXX XXX END

Open in new window

And if you are getting error [System.Object[]] doesn't contain a method named 'substring' then you must have more than one line in text file.. So you need to use -index 0 to get the first line..
((gc test.txt | Select-Object -Index 0).substring(28)).split(",")[0]
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Author Closing Comment

by:codedigger
ID: 38721560
Many thanks Subsun, right on the money, I appreciate the effort, it's the answer I've been looking for.
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