How to set environment variable within GDB using shell command?

When starting gdb from shell command-line, you can specify which program to run, with which arguments (with --args), and even modify the environment of the program with the help of env!

I just did it successfully like this:

gdb --ex=run --args env LD_BIND=now LD_DEBUG=libs \
apt-get install --yes $(cat pkgs-to-install-to-crash-apt)

--ex=run is to ask gdb to run it immediately.

In your case, you would do env -i.

It differs from the suggested env -i VAR=... gdb program in that only your examined program is under the special environment, but not gdb.

Option 2 is possible.

(gdb) unset environment
(gdb) python gdb.execute("set environment Myvar=\xff")
(gdb) show environment 
Myvar=ÿ

Option 1 can be done with env(1).

$ env -i MyVar=$(python -c 'print("xyz")') gdb
(gdb) show environment
MyVar=xyz
LINES=35
COLUMNS=80

Then you just have to clear LINES and COLUMNS.