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I want to run a program in an empty environment (i.e. with no envariables set). How to do this in bash?

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Possibly related: How to get a clean environment in a ksh shell – rahmu Sep 25 '12 at 9:14

2 Answers

up vote 14 down vote accepted

You can do this with env:

env -i your_program

Contrary to comments below, this does completely clear out the environment, but it does not prevent your_command setting new variables. In particular, running a shell will cause the /etc/profile to run, and the shell may have some built in settings also.

You can check this with:

env -i env

I.e. wipe the environment and then print it. The output will be blank.

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It doesn't completely clear out the environment: echo 'echo $PATH' > test.sh && chmod u+x test.sh && env -i test.sh prints /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin. – l0b0 Sep 24 '12 at 14:14
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However, it seems this is the closest you can get - It seems like variables like PATH, PWD and SHLVL are set automatically by Bash. +1. – l0b0 Sep 24 '12 at 14:31
@I0b0: See my edit. – ams Sep 24 '12 at 14:37
up vote 4 down vote

env -i -- somecommand runs a command in an empty environment, as ams has already mentioned.

A lot of programs rely on some important environment variables, so you may want to retain them:

env -i HOME="$HOME" LC_CTYPE="${LC_ALL:-${LC_CTYPE:-$LANG}}" PATH="$PATH" USER="$USER" -- somecommand

Alternatively, you could log in into a small login-time environment.

ssh localhost somecommand
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