Extracting information from a file of records

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Here's a very common application ...

You file a file of data records, and you want to parse the file handing the data record by record. Each record has a series of space delimited fields, most of which are no interest to you what so ever ...

And a template for a solution in Perl.

open (FH,--put file name here in quote--) or --handle error--

while ($report = <FH>) {

# Using list slices of anonymous lists to extract data

# $report = ("192.168.200.67 e-w-f graham mac 2005 17 Tiger mucky");

($cpuname,$yop) = (split(/\s+/,$report))[1,4];

print "$yop - $cpuname\n"; }

I dare say you were expecting a long example there, but in Perl I've done the whole thing in just six lines - and two of THEM are comments. The trick comes in the use of anonymous list slices:

(split(/\s+/,$report))[1,4];

"Take the string in $report. Divide it into a series of chunks, delimted at white space. But I'm only interested in returned fields 2 and 5 (i.e. numbers 1 and 4 because we start counting at zero).

Taking the data sample line I've included in my program sample, just the host computer name and the year of purchase are returned. No need for me to throw away explicitly the fields I don't want, and using
($cpuname,$yop) =
I can even assign each returned element to an appropriate scalar.

I might not do Perl as much as I used to , but I'm sure enjoying presenting the Perl Course this week!
(written 2008-01-16, updated 2008-01-17)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

P669 - Perl - Data Munging
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [2129] Nothing beats Perl to solve a data manipulation requirement quickly - (2009-04-14)
  [2702] First and last match with Regular Expressions - (2010-04-02)
  [3335] Practical Extraction and Reporting - (2011-06-26)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3764] Shell, Awk, Perl of Python? - (2012-06-14)
  [4620] Perl 6 - a Practical Extraction and Reporting example! - (2016-01-11)

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Some other Articles

Perl, PHP or Python? No - Perl AND PHP AND Python!
Summer Ball at Bowood - Saturday 12th July 2008
Buses from Well House Manor, Melksham, to Bath
Handling Binary data (.gif file example) in Perl
Extracting information from a file of records
How not to write Perl?
Comments on proposed Asda Superstore for Melksham
Ongoing Image Copyright Issues, PHP and MySQL solutions
Script to present commonly used images - PHP
Flooding by Asda-s proposed new supermarket

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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