hi i am new to perl, i have a doubt

Read perlintro#Simple substitution

    s/foo/bar/; # replaces foo with bar in $_
    $a =~ s/foo/bar/; # replaces foo with bar in $a
    $a =~ s/foo/bar/g; # replaces ALL INSTANCES of foo with bar in $a
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Combine with anchor

    $                   end of string
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perlintro also explains the safety net and string literals