Bash Shell Script Array Length Off By One

arraybash

The length of an array in my bash shell script appears to be off by one. I have 11 elements in a text file that I am reading in to an array, but my array length seems to be 12.

(( count = 0 ))
while read students[$count] ; do
    (( count++ ))
done < students.dat

echo $count

ArrayLength=$((${#students[@]}))

echo $ArrayLength

This code outputs:

11
12

The 11 makes sense since the count increment occurs after the read occurs and starts with 0–indicating 11 elements read in.

But the 12 is mysterious.

Here is the data file:

Ann
Bob
Cindy
Dean
Emily
Frank
Ginger
Hal
Ivy
Justin
Karen

(names appear on their own lines, but I couldn't format it that way in this post)

I've double checked with multiple utilities and there is NOT a blank line at the end of the file, or any trailing spaces on any line.

Best Answer

The last read that fails to find more data will assign an empty string, so the number of entries is one more than your data. To check that use printf "'%s'\n" "${students[@]}".

Related Solutions

Bash – how to count the length of an array defined in bash

You can access the array indices using ${!array[@]} and the length of the array using ${#array[@]}, e.g. :

#!/bin/bash

array=( item1 item2 item3 )
for index in ${!array[@]}; do
    echo $index/${#array[@]}
done

Note that since bash arrays are zero indexed, you will actually get :

0/3
1/3
2/3

If you want the count to run from 1 you can replace $index by $((index+1)). If you want the values as well as the indices you can use "${array[index]}" i.e.

#!/bin/bash

array=( item1 item2 item3 )
for index in ${!array[@]}; do
    echo $((index+1))/${#array[@]} = "${array[index]}"
done

giving

1/3 = item1
2/3 = item2
3/3 = item3

Bash Shell Script – How to Pass Array

AFAIK, you can't. You have to serialize it and deserialize it, e.g. via the argument array:

first

#!/bin/bash
ar=('foo' 'bar' 'baz' 'bat')
second "${ar[@]}" #this is equivalent to: second foo bar baz bat

second

#!/bin/bash
arr=( "$@" )
printf ' ->%s\n' "${arr[@]}"
<<PRINTS
   -> foo
   -> bar
   -> baz
   -> bat
PRINTS

A little bit of advice:

reserve all caps for exported variables
unless you have a very good specific reason for not doing so "${someArray[@]}" should always be double quoted; this formula behaves exactly like 'array item 0' 'array item 1' 'aray item 2' 'etc.' (assuming someArray=( 'array item 0' 'aray item 1' 'aray item 2' 'etc.' ) )

Best Answer

Related Solutions

Bash – how to count the length of an array defined in bash

Bash Shell Script – How to Pass Array

Related Question