global string replace

zX4hzjFWWT has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

perl -e '
   $string="X*X*X*X"; \
   $NEW=20;           \
   $string =~ s/(^|[\*])X([\*]|$)/${1}${NEW}${2}/g; \
   print "$string\n";'
[download]

will gives :

20*X*20*X

It seems that after first match, the first '*' which was used by 1st match, doesn't count for the 2nd match ..

Is there any modifier or another way to replace all the 'X' at once ? any trick without executing this line twice ?

Thank you very much !

edit: Thank you all for your answers, the ?= works beautiful.. very useful! :D

Comment on global string replace Select or Download Code

Replies are listed 'Best First'.
Re: global string replace by choroba (Cardinal) on Jun 07, 2019 at 09:35 UTC
Use a look-ahead assertion. It looks ahead, but doesn't advance the position: `s/(^\|\)X(?=\\|$)/$1$NEW/g # ~~~` [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: global string replace by jwkrahn (Abbot) on Jun 07, 2019 at 18:33 UTC
`perl -e' $string = "XXXX"; $NEW = 20; $string =~ s/ (?: ^ \| \ ) \K X (?= \* \| $ ) /$NEW/xg; print "$string\n"; ' 202020*20` [download]	[reply] [d/l]
Re^2: global string replace by AnomalousMonk (Archbishop) on Jun 07, 2019 at 19:11 UTC
NB: The regex `\K` operator (effectively, variable-width positive look-behind) is only available with Perl versions 5.10+. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]