in reply to regex to rename last _ with ,

Not sure just what you're doing since you don't post in  <code> ... </code> tags, but I think I would use a look-ahead: 

c:\@Work\Perl\monks>perl -wMstrict -le
"my @flist = qw(
   1st-device-CA_Eth.0/1
   2nd-device_TX_Gig.1/1
   3rd_device_MO_Gig.1/1
   );
 ;;
 for my $s (@flist) {
   print qq{'$s'};
   $s =~ s{ _ (?= [^_]* \z) }{,}xms;
   print qq{'$s'};
   print '';
   }
"
'1st-device-CA_Eth.0/1'
'1st-device-CA,Eth.0/1'

'2nd-device_TX_Gig.1/1'
'2nd-device_TX,Gig.1/1'

'3rd_device_MO_Gig.1/1'
'3rd_device_MO,Gig.1/1'

[download]

Replies are listed 'Best First'.
Re^2: regex to rename last _ with ,
by ArifS (Beadle) on Sep 11, 2014 at 13:49 UTC
    Thank you for the code.

    s{ _ (?= ^_* \z) }{,}xms;

    I would appreciate if someone could explain what it's doing for each part.
[reply]
       +----------------------------- In the scalar $s (interpreted as a str
+ing),
 |       +--------------------- if you find an _ (underscore)
 |       |   +----------------- that's followed by 0 or more of anythi
+ng but an _ (underscore) 
 |       |   |                  and then the end-of-string,    
 |       |   |             + -- replace it with a , (comma).
 |       |   |             |
 V       V   V             V
$s =~ s{ _ (?= [^_]* \z) }{,}xms;

      [download]

      Update: See "Look-Around Assertions" in the Extended Patterns of perlre.

      (And the use of  <code> ... </code> tags would still be much appreciated.)

      Another Update: If you have Perl version 5.10+, another way (see  \K in Extended Patterns): 

      c:\@Work\Perl\monks>perl -wMstrict -le
"use 5.010;
 ;;
 my @flist = qw(
   1st-device-CA_Eth.0/1
   2nd-device_TX_Gig.1/1
   3rd_device_MO_Gig.1/1
   );
 ;;
 for my $s (@flist) {
   print qq{'$s'};
   $s =~ s{ .* \K  _ }{,}xms;
   print qq{'$s'};
   print '';
   }
"
'1st-device-CA_Eth.0/1'
'1st-device-CA,Eth.0/1'

'2nd-device_TX_Gig.1/1'
'2nd-device_TX,Gig.1/1'

'3rd_device_MO_Gig.1/1'
'3rd_device_MO,Gig.1/1'

      [download]

[reply]
[d/l]
[select]
        And, for completeness: 
        xms
^^^
|||
|| Make . also match \n (not needed here).
||
| Make ^ and $ match beginning and end of lines (not needed here).
|
 Allow whitespace in the pattern for readability.

        [download]
        لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]
[d/l]
        Thank you very much. Much apprecaited!
[reply]

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