Gfyuki

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