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linuxbashenvironment-variablesld-preload

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

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?

Solution

  • 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.