shell adding string to an array

Question

I am having some trouble adding a string to an array within a loop. For some reason it always adds the same line. Here is my code:

declare -a properties
counter=0

while read line
do

    if [[ ${line} == *=* ]]
    then
        properties[${counter}]=${line}
        (( counter=counter + 1 ))
    fi
done < ${FILE}

for x in ${!properties[@]}
do
    echo "the value is $properties[x]"
done

For some reason each element in the array is the first line in the file. I must be doing something wrong, just not sure what.

Any help would be greatly appreciated

Change $properties[x] in your echo line to ${properties[$x]}... — twalberg
– twalberg, Commented Jan 14, 2014 at 20:36
The script will work in both bash and ksh93 if the declare ... is removed. Simple arrays are created on the fly in both. — Henk Langeveld
– Henk Langeveld, Commented Jan 15, 2014 at 16:57

anubhava · Accepted Answer · 2014-01-15 16:58:58Z

4

Try this script:

declare -a properties
while read line
do
   [[ "${line}" == *=* ]] && properties+=("$line")
done < "${FILE}"

for x in "${properties[@]}"
do
   echo "the value is "$x"
done

edited Jan 15, 2014 at 16:58

answered Jan 14, 2014 at 18:56

anubhava

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2 Comments

mklement0 Over a year ago

Great improvement, but please double-quote ${properties[@]} to prevent unwanted shell expansions.

Henk Langeveld Over a year ago

This eliminates the bug in the original script by looping x over the expanded values, instead of the index. The changes in the upper loop detract from the original bug.

Community · Accepted Answer · 2017-05-23 12:06:45Z

1

As @twalberg mentions in this comment, the problem is not in the top loop, but in the bottom one:

for x in ${!properties[@]}
do
    echo "the value is $properties[x]"
done

Array references always need braces { ... } to expand properly.

For some reason each element in the array is the first line in the file.

Not so. The array is correctly populated, but you need to change the reference to the array from:

echo "the value is $properties[x]"

to:

echo "the value is ${properties[x]}"

Just a simple oversight.

edited May 23, 2017 at 12:06

CommunityBot

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answered Jan 15, 2014 at 16:50

Henk Langeveld

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1 Comment

mklement0 Over a year ago

+1 for explaining the problem and showing me that variable references in array subscripts need not be $-prefixed ([x] vs. [$x]) (and that subscripts can even be arithmetic expressions).

DopeGhoti · Accepted Answer · 2014-01-14 18:56:41Z

0

A much simpler way to add an element to an array is to simply use the syntax:

VARNAME+=("content")

Also, as written, your bug may be here:

(( counter=counter + 1 ))

It probably should be one of these three:

(( counter=$counter + 1 ))
counter+=1
counter=$[$counter+1]
counter=$(($counter + 1))

answered Jan 14, 2014 at 18:56

DopeGhoti

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2 Comments

mklement0 Over a year ago

Your recommendation for building the array is helpful, but please consider removing the rest of your answer: Not only is (( counter=counter + 1 )) correct (albeit clumsy), your alternatives are not an improvement and in the case of counter+=1 incorrect. If anything, (( ++counter )) is the most concise form to use.

Henk Langeveld Over a year ago

Correct, but does not answer the question. And then, you missed an option: [[ ${line} == *=* ]] && properties[counter++]=${line} :-)

javaPlease42 · Accepted Answer · 2014-01-14 23:08:36Z

0

This KornShell (ksh) script worked fine for me. Let me know if anything.

readFileArrayExample.ksh

#! /usr/bin/ksh

file=input.txt
typeset -i counter=0

while read line
do
    if [[ ${line} == *=* ]]; then
        properties[${counter}]="${line}"
        ((counter = counter + 1))
        echo "counter:${counter}"
    fi
done < "${file}"

#echo ${properties[*]}

for x in "${properties[@]}"
do
    echo "${x}"
done

readFileArrayExample.ksh Output:

@:/tmp #ksh readFileArrayExample.ksh
counter:1
counter:2
counter:3
a=b
a=1
b=1
@:/tmp #

input.txt

a-b
a+b
a=b
a=1
b=1
1-a

answered Jan 14, 2014 at 23:08

javaPlease42

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