env -i x=9 bash -c 'x=4;bash -c "echo x: /\$x/"' # then try w/o 'x=9'
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From: Name withheld by request on 15 May 2010 19:52 Bug or feature? Pls explain: /tmp $ env -i bash -c 'x=4;bash -c "echo x: /\$x/"' x: // /tmp $ env -i x=9 bash -c 'x=4;bash -c "echo x: /\$x/"' x: /4/ --snip ~ $ uname -r; echo $BASH_VERSION 2.6.27.41-170.2.117.fc10.i686 3.2.39(1)-release -- thx
From: Michael Paoli on 20 May 2010 12:34
On May 15, 4:52\xa0pm, anonb6e9(a)nyx3.nyx.net (Name withheld by request) wrote: > Bug or feature? Pls explain: Feature > /tmp $ env -i bash -c 'x=4;bash -c "echo x: /\$x/"' > x: // In the above case, x is never set in or exported to the environment, thus when a new shell is started and x examined, it's unset. > /tmp $ env -i x=9 bash -c 'x=4;bash -c "echo x: /\$x/"' > x: /4/ In the example above, x is set in the environment to 9, then it's changed to 4, then it's examined. Some similar examples (comments preceded by //) // we unset x, so it's neither in the environment, nor shell // variable/parameter $ unset x $ env | sed -ne 's/^x=/set to &/p' // and one can see it's not in the environment // using this syntax, we can set it just for the environment of the env // command $ x=2 env | sed -ne 's/^x=/set to &/p' set to x=2 // we can then see it's no longer there for subsequent invocation $ env | sed -ne 's/^x=/set to &/p' // now we set it as shell variable/parameter $ x=2 $ set | sed -ne 's/^x=/set to &/p' set to x=2 // we can see it's set as shell variable/parameter, but not present in // the environment $ env | sed -ne 's/^x=/set to &/p' // now we export it to the environment $ export x // and we can now see it's in the environment $ env | sed -ne 's/^x=/set to &/p' set to x=2 // changing it, even when it's exported to the environment, doesn't // change it for ancestor (parent, etc.) PID(s) $ echo $$.$x; sh -c 'echo $$.$x; x=4; echo $$.$x'; echo $$.$x 5169.2 17754.2 17754.4 5169.2 $ |