Array Declaration (BASH)

[blendmaster]

Hello!

So, basically I'm new to bash (I have Java experience mostly, so I'm still a little off from scripting).

My problem lies in array declaration. Say I have an array album_Data, and I want to declare it with a certain amount of empty elements (say, for example, I want it to have $num_Of_Lines as the number for how big the array is).

After declaring it with empty elements, I want to begin initializing each element in a while loop. So, I have element $count being initialized in that array.

Finally, I want to then retrieve that data from the array.

As an example of the code (this is wrong, but may give a better picture):


num_Of_Lines=10
album_Data=album_Data[num_Of_Lines]
count=0
while read line3; do
if [ "$count" -le "4" ]; then
album_Data[$count]=$line3
((count++))
fi
done < Album.txt
mkdir /home/user/Music/"${album_Data[2]}"/

So basically, what am I doing (horridly, probably) wrong with my code?

Thank you!

[stefanadelbert]

As I understand it, you don't need to allocate space for an array in a Bash script. You declare an array and then populate it as you need to. If you need to iterate through an array there is a "for element in array" construct that is useful, or you could find the length of the array once it's populated and loop through the way you are in your example.

http://www.tech-recipes.com/rx/635/bash-shell-script-declaringcreating-arrays/
http://www.tech-recipes.com/rx/636/bash-shell-script-iterate-through-array-values/

There are plenty of good Bash scripting resources out there. Good luck.
Stefan

[blendmaster]

That would explain it.

Thanks, I was really going crazy with that.

I was looking all over the place for a way to declare arrays, when its not even a standard part of the language lol.

[gnusci]

To recommend these two sites for Bash:

http://en.tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html
http://www.tldp.org/LDP/abs/html/index.html

Give them a look if you are doing scripting.

[ghostdog74]

Hello!

So, basically I'm new to bash (I have Java experience mostly, so I'm still a little off from scripting).

My problem lies in array declaration. Say I have an array album_Data, and I want to declare it with a certain amount of empty elements (say, for example, I want it to have $num_Of_Lines as the number for how big the array is).

After declaring it with empty elements, I want to begin initializing each element in a while loop. So, I have element $count being initialized in that array.

Finally, I want to then retrieve that data from the array.

As an example of the code (this is wrong, but may give a better picture):


num_Of_Lines=10
album_Data=album_Data[num_Of_Lines]
count=0
while read line3; do
if [ "$count" -le "4" ]; then
album_Data[$count]=$line3
((count++))
fi
done < Album.txt
mkdir /home/user/Music/"${album_Data[2]}"/

So basically, what am I doing (horridly, probably) wrong with my code?

Thank you!

if its not for practicing bash arrays, what you want to do is just


var=$(awk 'NR==3' album.txt)
mkdir /home/user/Music/$var


tools like grep/sed/awk/cut/wc etc that are able to iterate files internally and faster than using bash's while loops.