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Top Forums Shell Programming and Scripting Use of awk and printf - help needed Post 302749611 by Don Cragun on Friday 28th of December 2012 05:48:04 PM
Old 12-28-2012
Quote:
Originally Posted by LDHB2012
That's amazing.

It worked the first time around. I really appreciate your help on this.

If you could answer a qusetion... I'm having trouble finding a tutorial or information on the "l - 13" or "l - 9" portion of the code.

I read the man on awk for substr (which is vague and confusing) and I'm just curious how I can make myself fluent in this language without having to pull my hair out and ask a billion questions.... If you could give me some insight on that, I'd really appreciate it.

-David

Happy New Year!

---------- Post updated at 05:27 PM ---------- Previous update was at 05:12 PM ----------

I KIND OF understand what it's saying but not quite.

substr($1, l - 13, 4)

The above looks like it's starting the count, 4 from the end, 13 to the left, which goes over 2012.

substr($1, l - 9, 2)
The above starts the count 2 from the end, 9 to the left, which is right between the 2012 and 12, which seems perfect. Am I missing something here? (obviously I am.)
Hi David,
The awk command l=length($1) sets l to the number of characters in the first field. In your example, this sets l to 35 because there are 35 characters in "20120727-files.files:20120727090044" (not counting the terminating null byte). The substr(x, s, c) returns c characters from the string x starting with the sth character in the string. So, substr($1, l - 13, 4) returns 4 characters from 20120727-files.files:20120727090044 starting with the 22nd character (i.e., "2012"). When a count isn't given (as in substr($1,l - 1)), substr() will return the remainder of the string from the given starting point. This is all done because I assume that the files.files portion of your input lines may vary in length, but we know that the timestamp is always the last 14 characters in the string.
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bytes(3pm)						 Perl Programmers Reference Guide						bytes(3pm)

NAME
bytes - Perl pragma to force byte semantics rather than character semantics NOTICE
This pragma reflects early attempts to incorporate Unicode into perl and has since been superseded. It breaks encapsulation (i.e. it exposes the innards of how the perl executable currently happens to store a string), and use of this module for anything other than debugging purposes is strongly discouraged. If you feel that the functions here within might be useful for your application, this possibly indicates a mismatch between your mental model of Perl Unicode and the current reality. In that case, you may wish to read some of the perl Unicode documentation: perluniintro, perlunitut, perlunifaq and perlunicode. SYNOPSIS
use bytes; ... chr(...); # or bytes::chr ... index(...); # or bytes::index ... length(...); # or bytes::length ... ord(...); # or bytes::ord ... rindex(...); # or bytes::rindex ... substr(...); # or bytes::substr no bytes; DESCRIPTION
The "use bytes" pragma disables character semantics for the rest of the lexical scope in which it appears. "no bytes" can be used to reverse the effect of "use bytes" within the current lexical scope. Perl normally assumes character semantics in the presence of character data (i.e. data that has come from a source that has been marked as being of a particular character encoding). When "use bytes" is in effect, the encoding is temporarily ignored, and each string is treated as a series of bytes. As an example, when Perl sees "$x = chr(400)", it encodes the character in UTF-8 and stores it in $x. Then it is marked as character data, so, for instance, "length $x" returns 1. However, in the scope of the "bytes" pragma, $x is treated as a series of bytes - the bytes that make up the UTF8 encoding - and "length $x" returns 2: $x = chr(400); print "Length is ", length $x, " "; # "Length is 1" printf "Contents are %vd ", $x; # "Contents are 400" { use bytes; # or "require bytes; bytes::length()" print "Length is ", length $x, " "; # "Length is 2" printf "Contents are %vd ", $x; # "Contents are 198.144" } chr(), ord(), substr(), index() and rindex() behave similarly. For more on the implications and differences between character semantics and byte semantics, see perluniintro and perlunicode. LIMITATIONS
bytes::substr() does not work as an lvalue(). SEE ALSO
perluniintro, perlunicode, utf8 perl v5.16.3 2013-02-26 bytes(3pm)
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