3 ms·

$ cat foo.sh #!/bin/bash echo $BASH_VERSION unset filename if [[ $filename == "foo" ]]; $ ./foo.sh 4.1.2(1)-release ./foo.sh: line 5

$ cat foo.sh #!/bin/bash echo $BASH_VERSION unset filename if [[ $filename == "foo" ]]; $ ./foo.sh 4.1.2(1)-release ./foo.sh: line 5: syntax error: unexpected end of file If $filename evaluates to an empty string, then the last line of code becomes if [[ == "foo" ]]; Similarly, if $filename evaluates to a b c, then the last line of code becomes if [[ a b c == "foo" ]]; The bash interpreter has problems with both of these.

nescafe 15y ago
No, that is just wrong. In double-brackets, bash will handle expansion and testing of unset variables and variables with spaces just fine, because word splitting and pathname expansion are not performed in double braces -- they are shell syntax, as opposed to single brackets, which are commands. Your syntax error happened because you don't have a fi matching that if. As a counterexample: (echo $BASH_VERSION; foo=foo; [[ $foo = foo ]] && echo $foo; foo="1 2 3"; [[ $foo = "1 2 3" ]] && echo $foo; foo=''; echo ${foo?"No foo for you"}; unset foo; echo ${foo?"No foo for you"}) 4.2.10(1)-release foo 1 2 3 bash: foo: No foo for you That last one is one of the few ways you can tell whether a variable is unset or merely set to an empty string. lrn2bash.