m/
    (?=^[^a]*a[^a]*$) ## One a and no other a's
    (?=^[^b]*b[^b]*$) ## One b and no other b's
    (?=^[^c]*c[^c]*$) ## One c and no other c's
    ^.{3}$            ## Exactly three chars
/x and print "$_: matched" for 'aaa'..'ccc';;

abc: matched
acb: matched
bac: matched
bca: matched
cab: matched
cba: matched

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In reply to Re: REgular expression to check the string that allows "a","b" and "c" to occur only once in any order. by BrowserUk
in thread REgular expression to check the string that allows "a","b" and "c" to occur only once in any order. by isha

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