Extract the data within the polygon

Hi…
I have observation points as shown in the attached figure (test.jpg).
I want to extract out the points which are within the grey box.
I tried with psclip and psmask but they are unable to do that.

Could you probably help me how to make it successfully?
Really appreciate for all you help

Regards
Piyush

gmtselect?..

Thank you #Joaquim. It works absolutely fine for me.