Environment Variables – Finding Files Setting or Adding Variables and Their Precedence

environment-variables

Some of my environment variables ($PATH, $MANPATH and friends) are partially set up in different source files.

I find myself wishing for a command or method to quickly gather what part, in a specific environment variable, came from what file.

My $PATH, for instance, has obviously been set (added to) in .bashrc, /etc/paths, /etc/paths.d/X11 … and I'm still looking for that last mysterious file which superfluously created a duplicate path definition in my $PATH.

It takes a good while to manually pinpoint the files that contribute to environment variables. There must be a useful way to bypass this unnecessary labor of tracing all the setters … or am I the only one thinking along these lines?

Best Answer

Typically PATH is set to an initial value in a highly system-dependent way by the program that logs you in (pam_env is a common contributor), then /etc/profile and ~/.profile and files that they include go on to modify that value.

Remove any change to PATH in .bashrc, environment settings don't belong in .bashrc: see Difference between .bashrc and .bash_profile.

First try logging in in text mode (e.g. with ssh localhost), as the session startup is a lot simpler than in graphics mode.

Put set -x at the beginning of /etc/profile and ~/.profile. The shell will print a trace of what it does on its standard error stream; look for assignments to PATH in the trace.

There is no notion of precedence to environment variable assignments: whoever assigns last wins.

Related Solutions

Bash Variables – Difference Between Exported and Non-Exported Shell Variables

Exported variables are carried into the environment of commands executed by the shell that exported them, while non-exported variables are local to the current shell invocation. From the export man page:

The shell shall give the export attribute to the variables corresponding to the specified names, which shall cause them to be in the environment of subsequently executed commands.

set outputs the current environment, which includes any local non-exported variables. env is used to launch programs in a new environment, and with no arguments will output what that new environment would be. Since env is creating a new environment, only exported variables are brought through, as is the case for any program launched from that shell. For example, spawning a second shell within the first (I used $$ to represent prompts in the inner shell):

$ FOO=BAR
$ bash
$$ echo $FOO             # Note the empty line

$$ exit
$ export FOO
$ bash
$$ echo $FOO
BAR
$$

Note that it's the variable that's exported, not just its value. This means that once you export FOO, FOO becomes a global variable and shows up in subsequent environments, even if changed later:

$ export FOO
$ FOO=BAR
$ bash
$$ echo $FOO
BAR
$$

Best Answer

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Bash Variables – Difference Between Exported and Non-Exported Shell Variables

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