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This article shows some ways to read lines from a file and load them into an array using Bash.

First, we'll look at the readarray method. Afterwards, we'll look at a more general method for reading files into Bash arrays.

Read a file into an array using Bash using the readarray method

readarray is a function that comes with Bash 4.0. This method works with all Bash versions higher than 4.0.

If you want to see which version of Bash you are currently running, you can use the following command:

echo ${Bash_VERSION}

If your Bash version is lower than 4.0, you can skip to the next method since readarray won't work for you.

We will use a file called numbers.txt for all examples with the following content.

numbers.txt file:

1 1
2 1
3 1
4 1
5 1
6 1
7 1
8 1
9 1
10 1

The syntax for reading this file and saving its contents into an array is as follows:

readarray -t Arr < numbers.txt

Breaking down the syntax, we have readarray as the name of the command, -t will remove newlines, and Arr is the name of the array into which the file contents will be written. numbers.txt is the name of the file we want to read.

请注意, if the file you want to read is not in the same folder as your script, you should provide the full path to the file.

The contents of this array can be read, as shown in the following example:

echo ${Arr[1]}

The above code will output the line in array index 1, which is the second line of the file.

The output is:

2 1

To print out an entire array, use the following syntax:

echo ${Arr[@]}

The output of this will be:

1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 10 1

Reading a file into an array using a generic method using Bash

The syntax of the general method is as follows:

IFS=$'\r\n' GLOBIGNORE='*' command eval  'ArrName=($(cat filename))'

Reading this array would have similar syntax as shown in the previous example:

echo ${ArrName[1]}

The Bash line above will display the contents of array index 1. However, if we want to display the contents of the entire array, we can use:

echo ${ArrName[@]}

General Method Description

ArrName in the general syntax is the name of the array, and the filename after cat is the file name to be read. We will modify these two variables for our custom use.

IFSDefines the break characters, in this case \r and \n . \r is a carriage return character and \n is a line feed character.

On most modern systems you'll see \n used as a newline character.

GLOBIGNORE='*'is set to be safe to avoid weird edge cases with file names. It should be noted that due to the use of GLOBIGNORE, this command requires Bash (and may not necessarily work with other shells such as zsh or fish).

Another important point to note is that this solution is much slower than readarray . The only reason to use it is if your version of Bash is older than 4.0.