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w00t
Asked: 2010-12-30 06:19:52 +0800 CST

cannot unset env variables from script

  • 772

I am trying to unset all environment variables from within a script. The script runs fine but if I run env it still shows all the variables set.
If I run the command from CLI, it works and the variables are unset.

unset `env | awk -F= '/^\w/ {print $1}' | xargs`

Have any idea how to run this from a script?
Also, have any idea how to source /etc/profile from a script? This doesn't work either.

I need to set variables with same names but different paths, depending on the instances my users need.

Later edit:
ok, I ended up with this (rather not elegant, but whatever) solution: 

. script

which contains: 

unset `env | awk -F= '/^\w/ {print $1}'|egrep -v "HOSTNAME|TERM|SHELL|HISTSIZE|SSH_CLIENT|SSH_TTY|USER|LS_COLORS|KDEDIR|MAIL|PATH|INPUTRC|PWD|LANG|HISTIGNORE|SSH_ASKPASS|TEST|SHLVL|HOME|LD_ASSUME_KERNEL|LOGNAME|SSH_CONNECTION|LESSOPEN|HISTTIMEFORMAT|G_BROKEN_FILENAMES|_"|xargs`
source env_variable_file

Thanks!

scripting bash environment-variables source

3 Answers

  1. Best Answer

    This is a standard answer, basically. You can't do that, because the script runs in a new child process. That process gets its own environment, and can't change that of the parent, either to set variables or to unset them.

    You can run the script in the current environment using the . command. And you can source /etc/profile in the same way:

    . /etc/profile

    • 11

  2. I tried to run your script and it does not work for me.

    I google a bit and found this:

    unset $(/usr/bin/env | egrep '^(\w+)=(.*)$' | \
egrep -vw 'PWD|USER|LANG' | /usr/bin/cut -d= -f1);

    This one actually works ;-)

    For sourcing files

    source /etc/profile

    is the right way as you said.

    If I modify your script like this

    unset $(env | awk -F= '{print $1}' | xargs)

    it also works.

    I do not think if there is any difference running the command interactively vs from a script.

    • 3

  3. Use -v to the unset command to rip items out of the environment; note at the end of this test script how you may get errors because we've unset $PATH so it can't find programs like 'id' and such.

    #!/bin/sh

LIST=`env | awk -F= '/^\w/ {print $1}' | xargs`

for item in $LIST; do
  echo "$item = ${!item}";
done

unset -v $LIST

for item in $LIST; do
  echo "$item = ${!item}";
done

HISTSIZE=5555
echo $HISTSIZE
source /etc/profile
echo $HISTSIZE
    • 0