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perl -i -0777 -pe 's/(\bAAAA )(QQQQ)(PPPP)( BBBB\b.*?\bCCCC XXXX )\2\3 +\b/$1$2$3$4$2/sg' /tmp/f
blah stuff AAAA QQQQPPPP BBBB stuff ... more stuff blah and CCCC XXXX QQQQPPPP and more stuff.