CODEWITHSUNDEEP
bash
Ray Salemi
Ray Salemi

Reputation: 5913

Why does -d return true on empty variable

Assume I have not set the environment variable MY_DIR. Then I do this:

% if [ -d $MY_DIR ]; then
>  echo WHAT?
> fi
WHAT?

I don't get it. Why does -d return TRUE if the environment variable doesn't exist?

Upvotes: 1

Views: 57

Answers (1)

chepner
chepner

Reputation: 531683

Without quotes, word-splitting causes the empty string to disappear altogether, and the resulting command is [ -d ]. A single non-empty argument (] is ignored for the purpose of counting arguments) makes [ succeed. [ <word> ] is interpreted as [ -n <word> ], which tests that <word> isn't empty. [ -d ] is read as [ -n -d ] and always succeeds since -d isn't an empty string.

Use quotes.

if [ -d "$MY_DIR" ]; then  # when unset, equivalent to [ -d "" ] with two arguments

Upvotes: 2

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