How to store / load exported environment variables to / from a file
POSIXly, you can do:
# save
export -p > saved-env
...
# restore
blacklisted () {
case $1 in
PWD|OLDPWD|SHELL|STORAGE|-*) return 0 ;;
*) return 1 ;;
esac
}
eval '
export() {
blacklisted "${1%%=*}" || unset -v "${1%%=*}"
}
'"$(export -p)"
export() {
blacklisted "${1%%=*}" || command export "$@"
}
. saved-env
unset -f export
Note that for bash
not invoked as sh
, you'd need to issue a set -o posix
for that to work properly. Also with bash
versions prior to 4.4, sourcing the output of export -p
is potentially unsafe:
$ env -i 'a;reboot;=1' /bin/bash -o posix -c 'export -p'
export OLDPWD
export PWD="/"
export SHLVL="1"
export a;reboot;
ksh93 has a similar problem. yash
doesn't have that particular one, but still has problems with variable names starting with -
:
$ env -i -- '-p=' yash -c 'export -p'
export '-p'=''
export OLDPWD
export PWD='/'
Also beware of potential problems if you're not in the same locale when saving and restoring the variables.
bash-4.3$ locale charmap
ISO-8859-15
bash-4.3$ export Stéphane=1
bash-4.3$ export -p > a
bash-4.3$ LC_ALL=en_GB.UTF-8 bash -c '. ./a'
./a: line 5: export: `Stéphane=1': not a valid identifier
I found a way by using compgen -A export
to get the list of environment variables:
blacklisted () {
case $1 in
PWD|OLDPWD|SHELL|STORAGE) return 0 ;;
*) return 1 ;;
esac
}
env_save () { # Assume "$STORAGE/#1.sh" is empty
local VAR
for VAR in $(compgen -A export); do
blacklisted $VAR || \
echo "export $VAR='${!VAR}'" >> "$STORAGE/$1.sh"
done
}
env_restore () {
local VAR
for VAR in $(compgen -A export); do
blacklisted $VAR || \
unset $VAR
done
source "$STORAGE/$1.sh"
}