Creating an array from a text file in Bash

Solution 1:

Use the mapfile command:

mapfile -t myArray < file.txt

The error is using for -- the idiomatic way to loop over lines of a file is:

while IFS= read -r line; do echo ">>$line<<"; done < file.txt

See BashFAQ/005 for more details.

Solution 2:

mapfile and readarray (which are synonymous) are available in Bash version 4 and above. If you have an older version of Bash, you can use a loop to read the file into an array:

arr=()
while IFS= read -r line; do
  arr+=("$line")
done < file

In case the file has an incomplete (missing newline) last line, you could use this alternative:

arr=()
while IFS= read -r line || [[ "$line" ]]; do
  arr+=("$line")
done < file

Need alternative to readarray/mapfile for script on older version of Bash

Solution 3:

You can do this too:

oldIFS="$IFS"
IFS=$'\n' arr=($(<file))
IFS="$oldIFS"
echo "${arr[1]}" # It will print `A Dog`.

Note:

Filename expansion still occurs. For example, if there's a line with a literal * it will expand to all the files in current folder. So use it only if your file is free of this kind of scenario.

Solution 4:

Use mapfile or read -a

Always check your code using shellcheck. It will often give you the correct answer. In this case SC2207 covers reading a file that either has space separated or newline separated values into an array.

Don't do this

array=( $(mycommand) )

Files with values separated by newlines

mapfile -t array < <(mycommand)

Files with values separated by spaces

IFS=" " read -r -a array <<< "$(mycommand)"

The shellcheck page will give you the rationale why this is considered best practice.

Solution 5:

You can simply read each line from the file and assign it to an array.

#!/bin/bash
i=0
while read line 
do
        arr[$i]="$line"
        i=$((i+1))
done < file.txt