Setting a Variable in an if loop in Bash

Question

  animal_name=""

  if [[ -z "${!animal_name// }" ]]; then
   animal_name="doggo"
  fi
    
 echo sudo chmod ...... ${!animal_name}

Is there any way to reference a variable in bash?

Describe what you want to do and what the desired output is. — Cyrus, Aug 25 '20 at 21:42
@Cyrus in the case the variable does not exist, I was the animal_name to be set to "doggo". However, it always ends up being blank when I try to echo — lost9123193, Aug 25 '20 at 21:43
Set default content if variable is empty: `echo "${animal_name:=doggo}"` — Cyrus, Aug 25 '20 at 21:49

kiwibg · Accepted Answer · 2020-08-25T21:50:37.977

3

Ditch the "{}"

animal_name=""
if [[ -z "$animal_name" ]]; then
    animal_name="doggo"
fi

sudo chmod {flag} $animal_name

edited Aug 25 '20 at 21:50

answered Aug 25 '20 at 21:45

kiwibg

334
2
9

sorry made an edit. I have more thing happening in the echo. Can i still use this? – lost9123193 Aug 25 '20 at 21:47
Sure thing. :) I'll edit the answer to show your use case – kiwibg Aug 25 '20 at 21:49
One question though - why use the echo? Are you trying to execute chmod or print out the whole "chmod {flag} $animal_name"? – kiwibg Aug 25 '20 at 21:52

score 0 · Answer 2 · answered Aug 25 '20 at 21:47

0

I think your error is in line 3 (or 2, depending on how you look at it.)

animal_name=""

if [[ -z "${!animal_name// }" ]]; then # Error: event not found: animal_name//
animal_name="doggo"
fi

echo sudo chmod ...... $animal_name

The fix that I found was to remove the 2 slashes in "${!animal_name// }" and that worked for me.

answered Aug 25 '20 at 21:47

Base64__

97
8

Edited to include the `chmod ......`. Could you provide some more background? like do you have a file/executable named doggo? what's the purpose of `sudo chmod ...... {!animal_name}`? – Base64__ Aug 25 '20 at 21:50
oh i think im getting this mixed up with javascript... do you know what {!animal_name} means when I include {! }? – lost9123193 Aug 25 '20 at 21:59

score 0 · Answer 3 · answered Aug 26 '20 at 19:17

If you are just trying to make sure the variable has some value, you can use defaults.

echo sudo chmod ...... ${animal_name:-doggo}

This will use doggo is animal_name is empty, but will leave it empty.

$: animal_name=
$: echo sudo chmod ...... ${animal_name:-doggo}
sudo chmod ...... doggo
$: echo "[$animal_name]" # still empty
[]
$: animal_name=bob
$: echo sudo chmod ...... ${animal_name:-doggo} # doesn't change is already set
sudo chmod ...... bob

If you want animal_name to ALWAYS default to doggo thereafter, use = instead of - and it will assign it as well if it's empty.

echo sudo chmod ...... ${animal_name:=doggo}

so:

$: animal_name=
$: echo sudo chmod ...... ${animal_name:=doggo}
sudo chmod ...... doggo
$: echo "[$animal_name]" # this time it was set
[doggo]
$: animal_name=bob
$: echo sudo chmod ...... ${animal_name:=doggo} # doesn't change if already set
sudo chmod ...... bob

Heck, this is the answer Cyrus gave in the comments *yesterday*, lol... — Paul Hodges, Aug 26 '20 at 20:04

score 0 · Answer 4 · answered Aug 27 '20 at 03:31

Probably you mean indirection? This may help.

animal_name=""
doggo="I am doggo!"
if [[ -z "${animal_name}" ]]; then
  animal_name="doggo"
fi

echo sudo chmod ...... ${!animal_name}

The ${!animal_name} reference the value of doggo, so the output is:

sudo chmod ...... I am doggo!

Setting a Variable in an if loop in Bash

4 Answers4