Using arrays in bash

English Programming/Scripting
1

Hi,
I am trying to implement a simple bubble sort program in bash. However, I seem to be facing some problems while operating on arrays. So far, I have been using the Advanced Bash Shell Guide on tldp.org as my reference, but even the syntax given there does not seem to work. I would be grateful if someone here in this forum could try to look into this matter:

19 if ${array"$comp_pos"]} -lt ${array"$j"]} then
20 temp = ${array${comp_pos}]}
21 {array${comp_pos}]} = ${array${j}]}
22 {array${j}]}=$temp
23 fi

Thanks for going through this post.

I am getting the following error message:

8.sh: line 20: temp: command not found
8.sh: line 21: {array[2]}: command not found
8.sh: line 22: {array[1]}=: command not found
8.sh: line 20: temp: command not found
8.sh: line 21: {array[3]}: command not found
8.sh: line 22: {array[2]}=: command not found

2

temp="${array${comp_pos}]}"

There should be no spaces between the variable name and its values, so temp = somevalue is not correct. The above in bold is so change all accordingly (if you have others too)

Also, the if conditional is missing a closing square bracket and semi-colon at end… correct is (or one of the correct ways is): if … ]; then

Further, an array is called with ${value[pos]} while assigning an array is value[pos]=

3

I am afraid most of the error messages have nothing to do with the usage of arrays. The are just simple errors you made.

temp = ${array${comp_pos}]}

This means calling the command *temp *with two parameter fields:

  1. =
  2. what ${array${comp_pos}]} becomes after bash did all substitutions.
    What you probably want is:
temp=${array${comp_pos}]}

This means: asign what ${array${comp_pos}]} becomes after substitution to the variable temp.

{array${comp_pos}]} = ${array${j}]}

Again first the shell does some substitutions: it will e.g. substitute ${comp_pos} with 2 and I do not know what it will substitute *${j} *with and after that ${array[jresult]}. But the result will be something like:

{array[2]} = someresult

Maybe by now you will see that you not only made the same mistake as above (spaces where not allowed), but also forgot a $ as the first character.
Orr as ana alternative (i do not know what you want to achieve exactly) you wanted the { } removed.

In short you should better read what you have written, and then ask yourself: how many fases will this go through and what happens in every of those phases. The man pages of bash come to help here. This involves things like: alias substitution, parameter substitution. …, program exececution.

I will leave the rest to you. You can of course come back with further questions, but I advise you first to write some simple scripts to train yourself and find out about the wonderfull (im)possibilities of bash :slight_smile:

4

In the additional info Henk provided above, it seems you don’t really seem to understand one-dimentional arrays in Bash. I’ll give a very simple example how to create and call them…

for i in {1..3}; do
    myvar[i]="value$i"
done

echo "${myvar[li]}"[/li]```


in the for loop, some values get assigned to the 'myvar' arrays and later on we print them with 'echo ${myvar[*]}'  (the * in the array is used to report all array values and one can also use @ instead of * but there are minor differences so you'll have to read up a bit). More examples you can find about arrays - [Bash Arrays | Linux Journal](http://www.linuxjournal.com/content/bash-arrays)
5

Yes, i have got it. As I said before, I was trying to perform a bubble sort, and the fragment of the code tries to swap values, in case the condition is satisfied. From what I gathered from your replies, and the links where I was referred, I found that this is what the code should be:

if  "${array"$comp_pos"]}" -gt "${array"$j"]}" ] ; then
                        temp=${array"$comp_pos"]}
                        array"${comp_pos}"]=${array"$j"]}
                        array"$j"]=$temp
                        #echo "$temp"
     fi

So many thanks, microchip8 and hcw for your kind advice and help. Your help really did the trick for me. Thanks once again!

6

No problemo, ask anytime… and what? Henk and me get no reputation points? :stuck_out_tongue:

7

Was away for one and a half day. Look if your programming style improved immensly (with all the nice colours). But still no reps >:)

8

What can I say, Henk? Unthankful cretins… why do we even bother? :stuck_out_tongue:

9

I agree, but maybe the place where to click for it should be a bit more eye catching. I did not realy understand what it was for until, by incident, I read something about in a post.

In any case, he said: “it works”. And he said: “thank you”. Much more then many do :slight_smile: