Creating an array from a text file in Bash

Question

A script takes a URL  parses it for the required fields  and redirects its output to be saved in a file  file txt  The output is saved on a new line each time a field has been found    file txt  A Cat A Dog A Mouse  etc       I want to take file txt and create an array from it in a new script  where every line gets to be its own string variable in the array  So far I have tried       bin bash  filename file txt declare -a myArray myArray   cat   filename     for    i   0   i  lt  9   i     do   echo  Element   i     myArray  i    done   When I run this script  whitespace results in words getting split and instead of getting   Desired output  Element  0   A Cat  Element  1   A Dog  etc       I end up getting this   Actual output  Element  0   A  Element  1   Cat  Element  2   A Element  3   Dog  etc       How can I adjust the loop below such that the entire string on each line will correspond one-to-one with each variable in the array

User · Answer

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.

User · Answer

Use the mapfile command   mapfile -t myArray  lt  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   gt  gt  line lt  lt    done  lt  file txt   See BashFAQ 005 for more details

User · Answer

You can do this too   oldIFS   IFS  IFS    n  arr     lt 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

User · Answer

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  lt  file txt

User · Answer

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  lt  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  lt  file     Related    Need alternative to readarray mapfile for script on older version of Bash

User · Answer

This answer says to use  mapfile -t myArray  lt  file txt   I made a shim for mapfile if you want to use mapfile on bash  lt  4 x for whatever reason  It uses the existing mapfile command if you are on bash    4 x  Currently  only options -d and -t work  But that should be enough for that command above  I ve only tested on macOS  On macOS Sierra 10 12 6  the system bash is 3 2 57 1 -release  So the shim can come in handy  You can also just update your bash with homebrew  build bash yourself  etc   It uses this technique to set variables up one call stack

[arrays] Creating an array from a text file in Bash

Use mapfile or read -a

Don't do this

Files with values separated by newlines

Files with values separated by spaces

Examples related to arrays

Examples related to bash

Examples related to loops

Examples related to scripting

Examples related to variable-assignment