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up vote 1 down vote favorite

I have a problem with my bash array I was trying to read the file however the array allocated it in array[1] instead of 0 

#!/bin/bash
index=0
INPUT=BookDB.txt
OLDIFS=$IFS
IFS=:
i=0
book=()
[ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
while read bookname author price quantity sold
do
#echo "BookName : $bookname"
#echo "Author : $author"
#echo "Price : $price"
#echo "Quantity : $quantity"
#echo "Sold : $sold"

    book+=("$bookname")
    author+=("$author")
    price+=("$price")
    quant+=("$quantity")
    sold+=("$sold") 

 done < $INPUT
 IFS=$OLDIFS



 # Use c style for loop
 # get total subscripts in an array
 total=${#book[*]}
 # 
 for (( i=0; i<=$(( $total -1 )); i++ ))
  do
   echo $i "${book[$i]} "
 done

 total=${#author[*]}
 # 
 for (( i=0; i<=$(( $total -1 )); i++ ))
 do
  echo  $i "${author[$i]} "
 done

Here is the output of the file

Book

0 Harry Potter - The Half Blood Prince 
1 The little Red Riding Hood 
2 Harry Potter - The Phoniex 
3 Harry Potter - The Deathly Hollow 
4 Little Prince 
5 Lord of The Ring 
6 Three Little Pig 
7 All About Ubuntu 
8 Catch Me If You Can 
9 Happy Day

Author 

0  
1 J.K Rowling 
2 Dan Lin 
3 J.K Rowling 
4 Dan Lin 
5 The Prince 
6 Johnny Dept 
7 Andrew Lim 
8 Ubuntu Team 
9 Mary Ann 
10 Mary Ann

Somehow the array for author[0] is empty

share|improve this question
5  
There's one namespace for scalar and array variables, and in bash and ksh, arrays just extend scalar variables. $author is ${author[0]}, author=x or read author is assigning to author[0]. Use different variable names in your read statement. –  Stéphane Chazelas Jan 27 at 13:08
    
Thank you yes it works. –  Lennon Chia Jan 27 at 13:13
1  
BTW, you'd be better off using perl or awk for that rather than bash loops and arrays. –  Stéphane Chazelas Jan 27 at 13:38
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1 Answer

up vote 2 down vote

book is initialized to the empty array by the line book=(), so during the first run through the loop book+=("$bookname") sets the first element of the array book (i.e. ${book[0]}) to the first book name.

author is used sometimes as an array and sometimes as a scalar. In ksh and bash, when an array is referenced using a scalar syntax (i.e. anything other than ${VAR[INDEX]}), the first element of the array is used. Assigning to the variable in a way other than VAR=…, such as via the read builtin, sets the first element of the array. Conversely, if an array is expected, a scalar variable is treated as a one-word array. Thus:

  • On the first run through the loop, author contains the string J.K Rowling, then author+=("$author") sets it to a two-element array containing J.K Rowling twice.
  • On the second run through the loop, read sets ${author[0]} to Dan Lin, then author+=("$author") appends Dan Lin, yielding the three-element array ('Dan Lin' 'J.K. Rowling' 'Dan Lin').
  • …
  • On the last run, read sees an empty line, so it sets $bookname, ${author[0]} and the others to an empty string.

To fix this, use a different name for the loop variables and for the arrays where you accumulate the data.

titles=()
authors=()
prices=()
quantities=()
sales=()
while read title author price quantity sold
do
    titles+=("$title")
    authors+=("$author")
    prices+=("$price")
    quantities+=("$quantity")
    sales+=("$sold") 
 done < $INPUT
share|improve this answer
    
If your bash is new enough, there's a readarray command. –  Ricky Beam Jan 27 at 21:57
    
@RickyBeam readarray doesn't break the line into fields, so I don't see how it's useful here. –  Gilles Jan 27 at 22:04
    
Depends on the final purpose of his script. I don't see where 5 arrays are necessary, but we don't know what the final produce is supposed to do. –  Ricky Beam Jan 27 at 22:11
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