how to have conditional part in gdbinit based on the environnment

In the gdb manual there is this part:

if else

This command allows to include in your script conditionally executed commands. The if command takes a single argument, which is an expression to evaluate...

I can perform tests in my gdbinit when I use a numeric expression, like

if (42 == 42)
    print "42"
end

But when I want to perform a test on a String, like this:

if ("a" == "a")
    print "yes"
end

then I got an error when I start gdb:

.gdbinit:45: Error in sourced command file:
You can't do that without a process to debug.

I tried, unsuccessfully, to find documentation or examples for the expression syntax in order to write my conditional block.

What I want to achieve is to add a bunch of command based on an environment variable. So I need to have this kind of section in my gdbinit:

if ("${myEnvVar}" == "someSpecialValue")
    #my set of special values
end

How to achieve that ?

edit: looks like the easiest way is to use python to perform this kind of operation: How to access environment variables inside .gdbinit and inside gdb itself?

If there's no way to achieve this with 'pure' gdb commands, I guess that this question should be closed as a duplicate.

Solution

How to achieve that ?

If you have GDB with embedded Python (most recent GDB builds do), you have full power of Python at your disposal.

For example:

# ~/.gdbinit
source ~/.gdbinit.py

# ~/.gdbinit.py
import os

h = os.getenv("MY_ENV_VAR")
if h:
  print "MY_ENV_VAR =", h
  gdb.execute("set history size 100")
  # Put other settings here ...
else:
  print "MY_ENV_VAR is unset"

Let's see if it works:

$ gdb -q 
MY_ENV_VAR is unset
(gdb) q

$ MY_ENV_VAR=abc gdb -q 
MY_ENV_VAR = abc
(gdb)