How to add a string to a .txt file in all rows excluding few characters using sed or awk

With awk:

awk '$2~/^[A-Z][A-Z]/{ $2="PT_"$2 }1' xid.txt

The output:

xid: PT_SC48028 id: artf398444
xid: indv1000 id: indv24519
xid: PT_SC32173 id: artf398402
xid: PT_SC21033 id: artf398372
xid: 1001 id: tracker4868
xid: wiki1000 id: wiki10709
xid: proj1234 id: proj12556

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• $2~/^[A-Z][A-Z]/ - if the 2nd field starts with 2 uppercase letters

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Or sed approach:

sed -i 's/^\(xid:[[:space:]]*\)\([A-Z]\{2\}[^[:space:]]*\)/\1PT_\2/' xid.txt

sed option

sed -i -e 's/[A-Z][A-Z]/PT_&/' file

where

• -i edit in place
• -e command to execute