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Full Discussion: ksh pattern matching
Top Forums Shell Programming and Scripting ksh pattern matching Post 302165978 by drl on Sunday 10th of February 2008 08:43:03 AM
Old 02-10-2008
Hi.

The newer shells, ksh and bash, have a lot of syntactical elements that are easily confused with one another.

The "Pattern Substitution Operators" syntax:
Code:
${variable_name}

can have a number of substitution operations with #, %, etc. They use the meta-characters, *, [], and ? -- page 123 ff, Learning the Korn Shell, 2nd Edition ("LTKS").

The "Patterns and Regular Expression" syntax uses:
Code:
*(exp), ?(exp), !(exp) ...

which correspond to the usual syntax we find in grep, etc:
Code:
grep "e*" ...

These patterns could be used within double brackets, for example:
Code:
if [[ $var == *!(e)* ]]

but not with string operator syntax (as far as I know) -- page 113 ff, 144 ff.

The ksh I use (pdksh, even on Solaris) notes a bad substitution for what I think is the right thing, but bash does it correctly in my opinion. Here's an example:
Code:
#!/bin/bash -
#!/bin/ksh -

# @(#) s1       Demonstrate string operators.

echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version =o $(_eat $0 $1)

var='String operators rule!'
echo
echo " Replace e with _:"
echo ${var//e/_}

echo
echo " Replace everything except e with _:"
echo ${var//[^e]/_}

exit 0

Producing:
Code:
% ./s1
(Versions displayed with local utility "version")
Linux 2.6.11-x1
GNU bash 2.05b.0

 Replace e with _:
String op_rators rul_!

 Replace everything except e with _:
_________e__________e_

Perhaps someone will stop by with a better explanation or a better suggestion ... cheers, drl
 

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Devel::Refcount(3pm)					User Contributed Perl Documentation				      Devel::Refcount(3pm)

NAME
"Devel::Refcount" - obtain the REFCNT value of a referent SYNOPSIS
use Devel::Refcount qw( refcount ); my $anon = []; print "Anon ARRAY $anon has " . refcount($anon) . " reference "; my $otherref = $anon; print "Anon ARRAY $anon now has " . refcount($anon) . " references "; DESCRIPTION
This module provides a single function which obtains the reference count of the object being pointed to by the passed reference value. FUNCTIONS
$count = refcount($ref) Returns the reference count of the object being pointed to by $ref. COMPARISON WITH SvREFCNT This function differs from "Devel::Peek::SvREFCNT" in that SvREFCNT() gives the reference count of the SV object itself that it is passed, whereas refcount() gives the count of the object being pointed to. This allows it to give the count of any referent (i.e. ARRAY, HASH, CODE, GLOB and Regexp types) as well. Consider the following example program: use Devel::Peek qw( SvREFCNT ); use Devel::Refcount qw( refcount ); sub printcount { my $name = shift; printf "%30s has SvREFCNT=%d, refcount=%d ", $name, SvREFCNT($_[0]), refcount($_[0]); } my $var = []; printcount 'Initially, $var', $var; my $othervar = $var; printcount 'Before CODE ref, $var', $var; printcount '$othervar', $othervar; my $code = sub { undef $var }; printcount 'After CODE ref, $var', $var; printcount '$othervar', $othervar; This produces the output Initially, $var has SvREFCNT=1, refcount=1 Before CODE ref, $var has SvREFCNT=1, refcount=2 $othervar has SvREFCNT=1, refcount=2 After CODE ref, $var has SvREFCNT=2, refcount=2 $othervar has SvREFCNT=1, refcount=2 Here, we see that SvREFCNT() counts the number of references to the SV object passed in as the scalar value - the $var or $othervar respectively, whereas refcount() counts the number of reference values that point to the referent object - the anonymous ARRAY in this case. Before the CODE reference is constructed, both $var and $othervar have SvREFCNT() of 1, as they exist only in the current lexical pad. The anonymous ARRAY has a refcount() of 2, because both $var and $othervar store a reference to it. After the CODE reference is constructed, the $var variable now has an SvREFCNT() of 2, because it also appears in the lexical pad for the new anonymous CODE block. PURE-PERL FALLBACK An XS implementation of this function is provided, and is used by default. If the XS library cannot be loaded, a fallback implementation in pure perl using the "B" module is used instead. This will behave identically, but is much slower. Rate pp xs pp 225985/s -- -66% xs 669570/s 196% -- SEE ALSO
o Test::Refcount - assert reference counts on objects AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2011-11-15 Devel::Refcount(3pm)
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