On Tue, 2012-06-19 at 13:59 -0500, David Bailey wrote: > I'm having difficulty getting my password back for the bugs website, but I wanted to add that testing for USER == root doesn't seem to handle sudo: > > sudo echo $USER > > returns 'dave' for me. > This depends on when $USER is evaluated and (in a bash session) when the value is substituted for the variable name. In your example substitution will occur when bash parses the command line, i.e. 'dave' was substituted for $USER before sudo was executed. OTOH, if the substitution done is inside a simple script which is run under the control of sudo, then the substitution takes place within the environment established by sudo. Here you go: $ cat test #!/bin/bash echo $USER $ ./test kiwi $ sudo ./test root $ What happens is that this time no substitution happens when the command is parsed. Instead, sudo changes user to root and spawns a shell under that user. This shell executes the script by spawning a second shell (by executing #!/bin/bash as 'root') and this evaluates $USER and does the substitution. Of course, much the same applies if the value of USER is retrieved within a C program by calling getenv(): again, its a delayed evaluation that would happen after sudo has done its thing. Finally, take a look at the next version of my script and think about what it does: $ cat ./test #!/bin/bash if [ -n "$1" ] then echo $1 else echo $USER fi echo "Local USER is $USER" $ sudo ./test $USER kiwi Local USER is root $ sudo ./test root Local USER is root Martin
