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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?

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3 Answers

up vote 4 down vote accepted

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.

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Your PATH can be set anywhere, not just in your .bashrc file. Most likely your system has a file, /etc/profile and/or /etc/profile.local which sets a default path for all users on your system. User specific changes or additions to it might be set in your .profile file if they're not in your .bashrc, or you may just be using the default on your system.

If you want to makes changes that only affect you, I'd put them in your .profile using the following form:

export PATH=/new/directory:$PATH

thereby editing the current path rather than rewriting it entirely.

The "INVOCATION" section of man bash (or here) explains the difference between .profile and .bashrc, and so on, and which other files and read and in what order when you log in or start a shell.

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It is very unlikely that a mechanism for this exists. Just think about how many ways there are to change the value of an env variable in the shell.

You may have some luck with set -x though.

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