Perl:string substitution Pattern: ='abc...',

Niroj · #1 (**permalink**) 01-21-2009

Hi friends,

I want to substitute "a ='....'," with ":" in everywhere in a string using Perl.

Details:
----------
my $str= " c1='fgfasfgasggfgff.,akhkhahha', c2='bbbn', c3='hg5 sh' ";

Required o/p: $str= " c1:c2:c3 "

I tried as below:

$str=~ s/=\'.*\',/:/g ;

print "str= $str\n";

Acual o/p:

str= c1: c3='hg5 sh'

Please help me to get the required o/p..

Niroj · #2 (**permalink**) 01-21-2009

my $str=" c1='fgfasfgasggfgff.,akhk', c2='bbbn', c3='hg5 sh' ";
print "Before substitution-> $str\n";
$str=~ s/(=.*\'.*\'.*,?)/:/g;

print "After substitution-> str= $str\n";

o/p:
==============
Before substitution-> c1='fgfasfgasggfgff.,akhk', c2='bbbn', c3='hg5 sh'
After substitution-> str= c1:

But I need the below o/p..
================

str= c1:c2:c3

Here my problem is I am not able substitute ':' for " ='bbbn'," & "c3='hg5 sh' " doesn't end with a ","

plz help...

KevinADC · #3 (**permalink**) 01-21-2009

Code:

my $str = " c1='fgfasfgasggfgff.,akhk', c2='bbbn', c3='hg5 sh' ";
print "Before substitution-> $str\n";
$str =~ s/='[^']*',?/:/g;
print $str;

Niroj · #4 (**permalink**) 01-22-2009

Quote:

Originally Posted by KevinADC

Code:

my $str = " c1='fgfasfgasggfgff.,akhk', c2='bbbn', c3='hg5 sh' ";
print "Before substitution-> $str\n";
$str =~ s/='[^']*',?/:/g;
print $str;

o/p=> c1: c2: c3:

Thanks Kelvin ! But could plz explain How does it work for c3='hg5 sh'.
(c3='.....' does not end with a comma "," !!)?

And my 2nd query is why "$str =~ s/='.*',?/:/g;" gives o/p as "c:" , though it should stop at c2='...', bcoz c3='..' doesn't end with a comma..

KevinADC · #5 (**permalink**) 01-22-2009

Quote:

Originally Posted by Niroj

o/p=> c1: c2: c3:

Thanks Kelvin ! But could plz explain How does it work for c3='hg5 sh'.
(c3='.....' does not end with a comma "," !!)?

In the regexp you see ,?. In this context the ? symbol is a quantifier that means zero or one of whatever is to the left of it. So it will match zero or one comma.

Quote:

Originally Posted by Niroj

And my 2nd query is why "$str =~ s/='.*',?/:/g;" gives o/p as "c:" , though it should stop at c2='...', bcoz c3='..' doesn't end with a comma..

In your regexp you have used .* which means to match zero or more of anything as much as possible. This is called greedy matching. So it matches whatever is between the first single quote and the last single quote in the string. What you should have done was used .*? which means to match zero or more of anything but as little as possible. This is called stingy matching. But using the negated character class [^'] is actually more efficient then using .*? to achieve the same result.

Niroj · #6 (**permalink**) 01-22-2009

Thanks agn Kalvin! The below is the new one I need to solve. Here the same type of string is present but I want the o/p differently.

my $str = " c1 ='mmdnn, ,sdm = sm,m,jkjk',c2 = 'chj=kjk, khj ', c3='hhshhj, hsjh'";

print "Before substitution-> $str\n";

$str =~ s/[^= *'[^']*'] *, *?/:/g;

print "After substitution-> $str\n"; # Getting Wrong o/p

================================

But I need the o/p:
c1 ='mmdnn, ,sdm = sm,m,jkjk':c2 = 'chj=kjk, khj ':c3='hhshhj, hsjh'

Plz help...

Niroj · #7 (**permalink**) 01-22-2009

Quote:

Originally Posted by KevinADC

In the regexp you see ,?. In this context the ? symbol is a quantifier that means zero or one of whatever is to the left of it. So it will match zero or one comma.

In your regexp you have used .* which means to match zero or more of anything as much as possible. This is called greedy matching. So it matches whatever is between the first single quote and the last single quote in the string. What you should have done was used .*? which means to match zero or more of anything but as little as possible. This is called stingy matching. But using the negated character class [^'] is actually more efficient then using .*? to achieve the same result.

Thanks agn Kalvin! The below is the new one I need to solve. Here the same type of string is present but I want the o/p differently.

my $str = " c1 ='mmdnn, ,sdm = sm,m,jkjk',c2 = 'chj=kjk, khj ', c3='hhshhj, hsjh'";

print "Before substitution-> $str\n";

$str =~ s/[^= *'[^']*'] *, *?/:/g;

print "After substitution-> $str\n"; # Getting Wrong o/p

================================

But I need the o/p:
c1 ='mmdnn, ,sdm = sm,m,jkjk':c2 = 'chj=kjk, khj ':c3='hhshhj, hsjh'

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