Assuming that the {} aren't nested. 

$s ='25 {fred and barney} text 2.36 12.0 {bam bam} text {pebbles}';
$s =~ s[(\{.*?\})]{ local $_=$1; tr[ ][_]; $_}ge;
print $s;
25 {fred_and_barney} text 2.36 12.0 {bam_bam} text {pebbles}

[download]

You'll have to explain what you mean by substitute a variable.

Examine what is said, not who speaks.
1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.

In reply to Re: looking for a regex by BrowserUk
in thread looking for a regex by Anonymous Monk

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