readarray.md

mapfile and readarray

mapfile (an alias to readarray) is a handy way to make an array separated by newlines in bash. This can be used to read from stdin, from a file directly, or from process substitution. In any case you can use either mapfile or readarray interchangeably.

Example 1

Sample input 1

$ cat input
This is a file containing
multiple lines of 	whitespace delimited
text.  Lets see how mapfile deals with
them.

(Yes I just used cat inappropriately)

Create array 1

$ mapfile -t my_array < input

The array 1

$ declare -p my_array
declare -a my_array=(
	[0]="This is a file containing" 
	[1]=$'multiple lines of \twhitespace delimited' 
	[2]="text.  Lets see how mapfile deals with" 
	[3]="them."
)

$ for line in "${my_array[@]}"; do echo "$line"; done
This is a file containing
multiple lines of 	whitespace delimited
text.  Lets see how mapfile deals with
them.

Example 2

Sample input 2

$ ls -l
total 0
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file0
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file1
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file2
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file3
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file4

Create array 2

$ readarray -t my_array < <(ls -l)

The array 2

$ declare -p my_array
declare -a my_array=(
	[0]="total 0" 
	[1]="-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file0" 
	[2]="-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file1" 
	[3]="-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file2" 
	[4]="-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file3" 
	[5]="-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file4"
)

$ for line in "${my_array[@]}"; do echo "$line"; done
total 0
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file0
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file1
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file2
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file3
-rw-r--r--  1 jessebutryn  staff  0 Apr 11 15:37 file4