Why are “declare -f” and “declare -a” needed in bash scripts?

Question

Sorry for the innocent question - I\'m just trying to understand...

For example - I have:

$ cat test.sh
#!/bin/bash
declare -f testfunct

testfunct ()          


        

Answer 1

declare -f allows you to list all defined functions (or sourced) and their contents.

Example of use:

[ ~]$ cat test.sh
#!/bin/bash

f(){
    echo "Hello world"
}

# print 0 if is defined (success)
# print 1 if isn't defined (failure)
isDefined(){
    declare -f "$1" >/dev/null && echo 0 || echo 1
}

isDefined f
isDefined g
[ ~]$ ./test.sh 
0
1
[ ~]$ declare -f
existFunction () 
{ 
    declare -f "$1" > /dev/null && echo 0 || echo 1
}
f () 
{ 
    echo "Hello world"
}

However as smartly said gniourf_gniourf below : it's better to use declare -F to test the existence of a function.