I found
[ ! -f /etc/default/lxc-net ] || . /etc/default/lxc-net
in /etc/default/lxc on Ubuntu 16.04 which seems to be replacing (my own or package maintainer code)
[ -f /etc/default/lxc-net ] && . /etc/default/lxc-net
Since the test is counter-intuitive (in case of failure of the test about non-presence of the file run the command) I was wondering if it has any advantage over the &&-version.
Yes, if you care about the exit code of the compound statement. Try the following:
#! /bin/sh -
! "$@" || true
echo "$?"
"$@" && true
echo "$?"
then run it with true and false as arguments.
./script true
0
0
./script false
0
1
This is because short-circuit evaluation of boolean expressions.
In OP's example, let's suppose the file doesn't exist:
TRUE OR x = TRUE). You get a TRUE for the compound statement.FALSE AND x = FALSE). You get a FALSE for the compound statement.Exit codes are very important. Check What does set -e mean in a bash script? to see possible implications of set -e, trap and set -o pipefail.
-e option as one reason one might well care very much about exit codes.
trap instead of set -e. Besides that, there is the recommendation of also setting set -o pipefail.
a || b/a && b seems like the one place where you wouldn't care about the exit code of a w.r.t set -e, since set -e will only be triggered by the final command in the chain (the Bash manual says: "The ERR trap is not executed if the failed command is ... part of a command executed in a && or || list except the command following the final && or ||... These are the same conditions obeyed by the errexit (-e) option. " )
[ -f file ] is true when file exists and is a plain file.
[ ! -f file ] is true when file does not exist or is another file type.
So there is no real difference - except for readability.
