What is the logic behind how bash tests for true/false?
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}
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
}
bash
add a comment |
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
}
bash
2
Your update does not include enough information. Please (a) include the values ofTERM
,TMUX
, andTMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.
– John1024
Apr 7 at 23:34
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03
add a comment |
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
}
bash
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
}
bash
bash
edited Apr 8 at 2:07
Rui F Ribeiro
42k1483142
42k1483142
asked Apr 7 at 23:10
StevieDStevieD
1759
1759
2
Your update does not include enough information. Please (a) include the values ofTERM
,TMUX
, andTMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.
– John1024
Apr 7 at 23:34
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03
add a comment |
2
Your update does not include enough information. Please (a) include the values ofTERM
,TMUX
, andTMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.
– John1024
Apr 7 at 23:34
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03
2
2
Your update does not include enough information. Please (a) include the values of
TERM
, TMUX
, and TMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.– John1024
Apr 7 at 23:34
Your update does not include enough information. Please (a) include the values of
TERM
, TMUX
, and TMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.– John1024
Apr 7 at 23:34
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03
add a comment |
1 Answer
1
active
oldest
votes
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 $?
0
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
@StevieD Runset -x
and then run your code. This will show you how every step is evaluated.
– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The key is that 0
means true and 1
(or any other non-zero value) means false.
In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$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 $?
0
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
@StevieD Runset -x
and then run your code. This will show you how every step is evaluated.
– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
add a comment |
The key is that 0
means true and 1
(or any other non-zero value) means false.
In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$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 $?
0
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
@StevieD Runset -x
and then run your code. This will show you how every step is evaluated.
– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
add a comment |
The key is that 0
means true and 1
(or any other non-zero value) means false.
In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$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 $?
0
The key is that 0
means true and 1
(or any other non-zero value) means false.
In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$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
edited Apr 7 at 23:26
answered Apr 7 at 23:19
John1024John1024
48.6k5114129
48.6k5114129
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
@StevieD Runset -x
and then run your code. This will show you how every step is evaluated.
– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
add a comment |
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
@StevieD Runset -x
and then run your code. This will show you how every step is evaluated.
– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
– StevieD
Apr 7 at 23:25
1
1
@StevieD Run
set -x
and then run your code. This will show you how every step is evaluated.– John1024
Apr 7 at 23:30
@StevieD Run
set -x
and then run your code. This will show you how every step is evaluated.– John1024
Apr 7 at 23:30
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
Ah, shit. Forgot about that setting. I'll try it.
– StevieD
Apr 7 at 23:32
add a comment |
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2
Your update does not include enough information. Please (a) include the values of
TERM
,TMUX
, andTMUX_MAN_PANE
from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.– John1024
Apr 7 at 23:34
It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
– StevieD
Apr 7 at 23:46
It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
– StevieD
Apr 7 at 23:56
I should just be going this in perl. Fuck this crazy shit.
– StevieD
Apr 7 at 23:57
Jesus, finally figured it out. Posting solution.
– StevieD
Apr 8 at 0:03