egrep 或与

' HEADERABC'
egrep -ha '^.{1}(HEAD)' 1.txt | egrep -ha '^.{7}(A)' > 2.txt

'HEADERABC'
egrep -ha '^(HEAD)' 1.txt > 2.txt
egrep -ha '^.{0}(HEAD)' 1.txt > 2.txt

' HEADERABC'
' TAILER123'
egrep -ha '^.{1}(HEAD|TAIL)' 1.txt > 2.txt

' HEADERABC'
' TAILER123'
egrep -ha '^.{1}(HEAD).{2}(AB)|^.{1}(TAIL)' 1.txt > 2.txt