How to duplicate full word by partial match in sed

October 13, 2022

I have a file in which each line has the following format:

foo         tc_TESTNAME,  // TEST #1

I would like to duplicate tc_TESTNAME in each line as follows:

foo         tc_TESTNAME tc_TESTNAME,  // TEST #1

Following sed command only duplicates the matching part of the word:

# sed -e "s/(tc_*)/& &/"
foo         tc_ tc_TESTNAME,  // TEST #1

What is the correct regex syntax to duplicate the whole word?

>Solution :

With your shown samples please try following sed program.

sed -E 's/(tc_[^,]+)/\1 \1/' Input_file

OR: to match exact word starting from tc just in case you may have other strings then make sure space is present in regex like:

sed -E 's/ (tc_[^,]+)/ \1 \1/'  Input_file

Explanation: Using -E option to enable ERE(extended regular expression) and in main program using s option to perform substitution. Then matching (tc_[^,]+) which captures from tc_ just before next comma comes and capturing this value into 1 capturing group. While substituting it substitute it with itself space and itself as per required output.