Bash script error with cat and if

Question

I'm learning bash but now I'm having a lot of trouble making this script work:

#!/bin/bash

A="0"
B="0"
C="0"
D="0"
E="0"
F="0"
G="0"

while true; do

sleep 1

BATTERY='cat battery.txt'

if [["$BATTERY" -le 100] && ["$BATTERY" -gt 85] && [$A -eq 0]]; then

A="1"
    commands... 

elif [["$BATTERY" -le 85] && ["$BATTERY" -gt 70] && [$B -eq 0]]; then

B="1"
    commands...

elif [["$BATTERY" -le 70] && ["$BATTERY" -gt 55] && [$C -eq 0]]; then

C="1"
    commands...

elif [["$BATTERY" -le 55] && ["$BATTERY" -gt 40] && [$D -eq 0]]; then

D="1"
commands...

elif [["$BATTERY" -le 40] && ["$BATTERY" -gt 25] && [$E -eq 0]]; then

E="1"   
    commands...

elif [["$BATTERY" -le 25] && ["$BATTERY" -gt 10] && [$F -eq 0]]; then

F="1"
commands...

elif [["$BATTERY" -le 10] && ["$BATTERY" -gt 0] && [$G -eq 0]]; then

G="1"
commands...
fi
done

The error that I get when I execute this script is:

./changewill.sh: line 17: [[cat battery.txt: command not found
./changewill.sh: line 27: [[cat battery.txt: command not found
./changewill.sh: line 36: [[cat battery.txt: command not found
./changewill.sh: line 45: [[cat battery.txt: command not found
./changewill.sh: line 54: [[cat battery.txt: command not found
./changewill.sh: line 63: [[cat battery.txt: command not found
./changewill.sh: line 72: [[cat battery.txt: command not found

I have been reading and looking around and I think the cat output is correctly assigned to BATTERY. I tried with some different things like { [ ¨, but nothing works. And yes, the file exists and it's in the same folder with the script.

Any advice?

Are you running the script in the script's directory or having it in the path? — BugFinder, Sep 28 '12 at 08:16
Both `[[` and `[` need to be surrounded with spaces -- and see the [bash manual](http://www.gnu.org/software/bash/manual/html_node/index.html) for more information on [`[`](http://www.gnu.org/software/bash/manual/html_node/Bourne-Shell-Builtins.html#Bourne-Shell-Builtins) (look for "test") and [`[[`](http://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html#Conditional-Constructs). — Keith Thompson, Sep 28 '12 at 09:31

Mat · Accepted Answer · 2012-09-28T08:59:55.000

3

BATTERY='cat battery.txt'

That doesn't execute cat battery.txt, it just saves "cat battery.txt" as a string into that variable.

You should:

BATTERY=$(cat battery.txt)

or

BATTERY=`cat battery.txt`

(First form is preferred.)

Your tests have syntax errors too. Use for example:

elif [[ $BATTERY -le 10 && $BATTERY -gt 0 && $G -eq 0 ]]; then ...

[ and [[ are actually completely different things.

[ is the test program (check out ls /usr/bin/[ and man test), [[ expr ]] is a shell compound command (conditional expression).

edited Sep 28 '12 at 08:59

answered Sep 28 '12 at 08:19

Mat

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Why is the first form is better than the second? – Blender Sep 28 '12 at 08:20
It's easier to use if you need to quote things in the thing you're executing, or if you need to nest them. – Mat Sep 28 '12 at 08:21
I think this solved the problem with cat, but I'm still having this error: ./changewill.sh: line 17: [[30: command not found ./changewill.sh: line 27: [[30: command not found ./changewill.sh: line 36: [[30: command not found ./changewill.sh: line 45: [[30: command not found ./changewill.sh: line 54: [[30: command not found ./changewill.sh: line 63: [[30: command not found ./changewill.sh: line 72: [[30: command not found – HumiD Sep 28 '12 at 08:51
1

You need a space after `[` . Actually your tests all look real odd. – Mat Sep 28 '12 at 08:52

score 0 · Answer 2 · edited Sep 28 '12 at 09:26

0

To get the output of a command, you need to wrap the command with backticks, not quotes:

BATTERY=`cat battery.txt`
        ^               ^

edited Sep 28 '12 at 09:26

Keith Thompson

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answered Sep 28 '12 at 08:19

Blender

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score 0 · Answer 3 · answered Sep 28 '12 at 08:20

0

The correct syntax for conditions is

[[ $BATTERY -le 55 && $BATTERY -gt 40 && $D -eq 0 ]]

i.e. no single square brackets. For numeric comparison, you can use the double parentheses, too:

if (( BATTERY==55 && BATTERY > 40 && D == 0 )) ; then ...

answered Sep 28 '12 at 08:20

choroba

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Thanks, that was the problem! – HumiD Sep 28 '12 at 09:15
Single square brackets are also acceptable. `[` ... `]` and `[[` ... `]]` have different semantics; see the bash documentation for details. One of the problems in the code in the question is the lack of spaces around the square brackets. – Keith Thompson Sep 28 '12 at 09:25
This fails to address the problem that `BATTERY` is just a static piece of text, not (as was apparently intended) the contents of a file. The value of the variable is literally `cat battery.txt`. – tripleee Sep 28 '12 at 10:57

Bash script error with cat and if

3 Answers3