linux - grep command not working as my expectation -

i have text file mentioned below, , along pass input want corresponding output.

input file: test.txt

abc:abc_1 abcd:abcd_1 1_abcd:1_abcd_bkp xyz:xyz_2 

so if use abc above test.txt file, want abc_1; , if pass abcd, need abcd_1 output.

i tried cat text.txt | grep abc | cut -d":" -f2,2, getting output

abc_1 abcd_1 1_abcd_bkp 

when want abc_1.

with gnu grep:

grep -po "^abc:\k.*" file 

output:

 abc_1 

---

\k keeps text matched far out of overall regex match.