Rrerku

This:

$ echo $VAR
something

And this:

$ [[ -z "$VAR" ]]
$ echo $?
1

Yet this:

if [[ -z "$TMUX_MAN_PANE" ]]; then
 echo 'NEVER PRINTS!'

This screws with my head.

UPDATE

Here's some real code. I can't get this to work.

tmux_man_page() 
if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then
 tmux list-panes -t $TMUX_MAN_PANE &> /dev/null
 echo $?
 echo $TMUX_MAN_PANE
 [[ -z "$TMUX_MAN_PANE" ]]
 echo $?
 if ! [[ -z "$TMUX_MAN_PANE" ]] && [[ $? ]]; then
 echo luck
 tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1
 else
 echo fuck
 tmux split-window -vf man $1
 TMUX_MAN_PANE=$(tmux display-message -p "#pane_id")
 export TMUX_MAN_PANE
 tmux select-pane -t last
 fi
fi

UPDATE 2: Success

Finally figured it out. Was having problems getting the status of the first line in the if statement. Had to do some trickery to get the output of the tmux statement in the first line of the if statement. If anyone knows a cleaner way to do this, I'm all ears.

Here's the working code:

tmux_man_page() 
if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then
 fucker=$(tmux list-panes -t $TMUX_MAN_PANE 2>&1)
 if ! [[ -z "$TMUX_MAN_PANE" ]] && ! [[ $fucker =~ 'find pane' ]]; then
 tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1
 else
 tmux split-window -vf man $1
 TMUX_MAN_PANE=$(tmux display-message -p "#pane_id")
 export TMUX_MAN_PANE
 tmux select-pane -t last
 fi
fi


tmux_man_page_close() 
 if [ $TMUX_MAN_PANE ]; then
 tmux kill-pane -t $TMUX_MAN_PANE
 fi

The key is that 0 means true and 1 (or any other non-zero value) means false.

In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$VAR" ]] returns code zero (true) if $VAR is empty or one (false) if it is not empty:

$ var=""; [[ -z "$var" ]]; echo $?
0
$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?
1

In sum, if $VAR is non-empty, then [[ -z "$VAR" ]] is false (returns 1) and the then statement does not execute.

Did you intend for the test to return true if the variable was non-empty? If so, replace -z with -n:

$ var=""; [[ -n "$var" ]]; echo $?
1
$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?
0

For brevity, the same test is performed if -n is omitted:

$ var=""; [[ "$var" ]]; echo $?
1
$ var="NOT EMPTY"; [[ "$var" ]]; echo $?
0