Setting the LD_PRELOAD environment variable for commands run without typing the full path

Question

I'm playing around with LD_PRELOAD and have produced a library that simply wraps puts() in a function that converts the string to be printed to uppercase before printing. I then export the LD_PRELOAD variable as so

$ export LD_PRELOAD=/home/adrian/test/myputs.so

Now the behaviour works as expected when running the command

$ /bin/pwd
/HOME/ADRIAN/TEST

But it does not work when runing like this

$ pwd
/home/adrian/test

What is the mechanism that's causing the LD_PRELOAD environment variable to be ignored in this case?

score 4 · Accepted Answer · answered Apr 25 '12 at 09:27

4

Becausepwd is shell builtin command - see man bash or docs here. So if you write

$ pwd

Then the builtin command is launched. If you tell it the path, it will execute the ELF binary and use the LD_PRELOAD.

answered Apr 25 '12 at 09:27

Tomas

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2

Thanks! After a quick search I found I can disable the builtin pwd using `enable -n pwd` and now it behaves as expected. – eltommo Apr 25 '12 at 09:38
@eltommo, wow, I was not aware of this possiblity. Interesting! – Tomas Apr 25 '12 at 09:39

Setting the LD_PRELOAD environment variable for commands run without typing the full path

1 Answers1