Using Declare Inside a Function in Bash

Question

I am want to change a global variable (or at least append to it) using a function.

input="Hello"
example=input    

func() {
    declare -x $example="${input} World"
}

func
echo $input

The output of this would be "Hello" The original value. I would like it if the function were to able to change the original value. Is there alternative to accomplishing this. Please note I need to set example=input and then perform on the operation on example (the variable).

BTW, if I used eval instead the function will complain about World being a function or something.

Foo Bah · Accepted Answer · 2011-09-21 21:09:04Z

6

Did you try using export?

export $example="${input} World"

answered Sep 21, 2011 at 21:09

Foo Bah

26.4k5 gold badges58 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

zhaoxg · Accepted Answer · 2014-01-18 14:47:49Z

3

you should use

declare -x -g $example="${input} World"

in your func

The -g option forces variables to be created or modified at the global scope, even when declare is executed in a shell function. It is ignored in all other cases.

see

http://www.gnu.org/software/bash/manual/bashref.html

Also note in MinGW, it seems that declare does not support the -g option.

edited Jan 18, 2014 at 14:47

answered Jan 18, 2014 at 9:52

zhaoxg

312 bronze badges

1 Comment

DKebler Over a year ago

you can combine those declare -gx Also declare -x will export but only within the scope of the function. See related question stackoverflow.com/a/5785683/4695378

Mark Thompson · Accepted Answer · 2013-02-01 23:55:41Z

0

You could use eval by redefining func() as the following:

func() {
    eval $example=\"${input} World\"
}

This allows the double-quotes to "survive" the first parsing (which expands the variables into their values, as needs to be done) so that eval starts parsing again with the string 'input="Hello World".

As for the use of export to do the job, if the variable input does not actually need to be exported, include its '-n' option:

export -n $example=...

, and the variable remains a shell variable and does not get exported as an environment variable.

answered Feb 1, 2013 at 23:55

Mark Thompson

11

2 Comments

jsears Over a year ago

Using eval is generally frowned upon, because it opens you to command injection attacks if you have any untrusted user input.

papo Over a year ago

... if there is a better way. Bash <v4.3 does not support declare -g and if export would not work for specific case, eval would be the only option here. In this answer, script could be hacked by input='ha"; date; "' but easy fix is to add single quotes: eval '$example=\"${input} World\"' and this eval will be safe.

Collectives™ on Stack Overflow

Using Declare Inside a Function in Bash

3 Answers 3

Comments

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related