How do I perform a Perl substitution on a string while keeping the original

Question

In Perl  what is a good way to perform a replacement on a string using a regular expression and store the value in a different variable  without changing the original   I usually just copy the string to a new variable then bind it to the s    regex that does the replacement on the new string  but I was wondering if there is a better way to do this    newstring    oldstring   newstring    s foo bar g

User · Answer

I hate foo and bar    who dreamed up these non descriptive terms in programming anyway   my  oldstring    replace donotreplace replace donotreplace replace donotreplace    my  newstring    oldstring   newstring    s replace newword g    inplace replacement  print  newstring     newword donotreplace newword donotreplace newword donotreplace

User · Answer

The statement    my  newstring    oldstring     s foo bar g    Which is equivalent to   my  newstring    oldstring   newstring    s foo bar g    Alternatively  as of Perl 5 13 2 you can use  r to do a non destructive substitution   use 5 013       my  newstring    oldstring    s foo bar gr

User · Answer

This is the idiom I ve always used to get a modified copy of a string without changing the original   my  newstring    oldstring     s foo bar g   In perl 5 14 0 or later  you can use the new  r non-destructive substitution modifier  my  newstring    oldstring    s foo bar gr     NOTE  The above solutions work without g too  They also work with any other modifiers  SEE ALSO  perldoc perlrequick  Perl regular expressions quick start

User · Answer

If you write Perl with use strict   then you ll find that the one line syntax isn t valid  even when declared   With   my   newstring    oldstring     s foo bar     You get   Can t declare scalar assignment in  my  at script pl line 7  near        Execution of script pl aborted due to compilation errors    Instead  the syntax that you have been using  while a line longer  is the syntactically correct way to do it with use strict     For me  using use strict  is just a habit now   I do it automatically   Everyone should      usr bin env perl -wT  use strict   my  oldstring    foo one foo two foo three   my  newstring    oldstring   newstring    s foo bar g   print   oldstring    n   print   newstring    n

User · Answer

The one-liner solution is more useful as a shibboleth than good code  good Perl coders will know it and understand it  but it s much less transparent and readable than the two-line copy-and-modify couplet you re starting with   In other words  a good way to do this is the way you re already doing it   Unnecessary concision at the cost of readability isn t a win

User · Answer

Another pre-5 14 solution  http   www perlmonks org  node id 346719  see japhy s post   As his approach uses map  it also works well for arrays  but requires cascading map to produce a temporary array  otherwise the original would be modified    my  orig     this    this sucks    what is this     my  list   map   s this that        map         orig     orig unmodified

User · Answer

Under use strict  say    my  new    original     s foo bar     instead

[regex] How do I perform a Perl substitution on a string while keeping the original?

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