$ cat /etc/os-release 
NAME="Ubuntu"
VERSION="20.04.2 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.2 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal
 

$ dpkg -l flirc

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=================================
ii  flirc          3.25.3       amd64        no description given
 

$ ldd /usr/bin/flirc_util

        linux-vdso.so.1 (0x00007ffe453d8000)
        libreadline.so.6 => not found
        libusb-1.0.so.0 => /lib/x86_64-linux-gnu/libusb-1.0.so.0 (0x00007f7de9b4c000)
        libhidapi-hidraw.so.0 => /lib/x86_64-linux-gnu/libhidapi-hidraw.so.0 (0x00007f7de9b45000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f7de9b22000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7de9930000)
        libudev.so.1 => /lib/x86_64-linux-gnu/libudev.so.1 (0x00007f7de9903000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f7de9b7a000)

libreadline6 is not available in ubuntu, it would be best to update the package to use libreadline8, or libreadline5 which seems to be available still.

This may have been taken care of with 3.25.4 (if I could download the package I would check myself) but if not could you please add it to the todo list for 3.25.5.

The /usr/bin/Flirc gui works just fine, but others may want the command line.

A simple rebuild from the latest sources, seems to resolve the issue for me. 

Can you guys fix this on your end, by repackaging the flirc_util for Ubuntu, with the latest build? (Obviously, with regression testing!).