bash - Difference between chaining `test` and using an `if` statement -

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is there difference between:

[ -f $foo ] && do_something

...and:

if [ -f $foo ];   do_something fi

i thought equivalent, [ alias test, exits 0 when condition passes. however, in script have written, i'm checking whether environment variables set and, if not, bail out. in case:

[ -z "${my_env1+x}" -a -z "${my_env2+x}" ] && fail "oh no!"

...always seems bail out; when $my_env1 , $my_env2 are set. however, if version works correctly:

if [ -z "${my_env1+x}" -a -z "${my_env2+x}" ];   fail "oh no!" fi

...where fail defined as:

fail() {   >&2 echo "$@"   exit 1 }

i cannot diagnose source of problem answering question in title, difference between first && second , if first; second; fi know.

if first evaluates true, there no difference.

if first evaluates false, result of entire expression first && second false. if shell has -e flag set, cause abort. version using if statement, on other hand, never produce result if first evaluates false shell continue happily if -e set.

therefore, write more verbose if first; second; fi if cannot afford failure status. can important, example, when writing makefiles or if make general habit run scripts -e.


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