I want to run a program in an empty environment (i.e. with no envariables set). How to do this in bash?
Answers:
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Method 1
You can do this with env
:
env -i your_command
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.
Method 2
A “clean” bash
environment may be had with
$ env -i bash --noprofile --norc
-
The
env -i
command executes the command given to it on the command line without transferring any of the exported environment variables of the old shell environment to the environment of the executed program. -
The
--noprofile
option stopsbash
from reading the system-wide or personal shell initialization scripts that would otherwise be read for a login shell. -
The
--norc
option stopsbash
from reading the personal shell initialization scripts that would otherwise be read for an interactive shell.
Method 3
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
Method 4
While the accepted answer is correct, what you usually want to do is to:
env -i HOME="$HOME" bash -l -c "printenv; and any other commands"
This gives you bare but functional bash (same as you’d get when login in non-interactive mode). This for example sets the language, timezone, HOME, etc.
Edit: Added HOME="$HOME"
based on excellent answer here: https://unix.stackexchange.com/a/451389/100093
Method 5
The problem with most answers here is that env -i
clears HOME
, so even if you run bash -l
on the inside, it won’t read your .bash_profile
etc. If what you’re looking for is a shell that acts as if you had just done a fresh login, you’d want this instead:
env -i HOME="$HOME" bash -l -c 'your_command'
Example:
$ export ABC=123 $ env -i HOME="$HOME" bash -l -c 'env' | grep ABC $ env HOME="$HOME" bash -l -c 'env' | grep ABC ABC=123
Method 6
If you want to ensure a script has a clean environment you can alter the shebang line like this little example illustrates:
#!/usr/bin/env -S -i bash env
which displays its environment like this
PWD=/home/myuser/mydir SHLVL=1 _=/usr/bin/env
Here, we run the bash
shell through env
which takes an -i
argument that instructs it to clean the environment. The -S
is required when passing multiple arguments on shebang lines.
Method 7
To answer balki’s comment (and answering my own question in the process :-):
% echo Environment in calling shell: vars: $(env |wc -l); echo; ./du; echo; cat du Environment in calling shell: vars: 43 ==> This is the environment: vars: 5 PATH="$PATH" PWD=/Users/nick SHLVL=1 SOMETHING_TO_KEEP="$USER" _=/usr/bin/env ==> The end. #!/usr/bin/env -i SOMETHING_TO_KEEP="$USER" PATH="$PATH" /bin/sh echo "==> This is the environment: vars:" $(/usr/bin/env | /usr/bin/wc -l) /usr/bin/env echo "==> The end."
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0