Read lines from a file into a Bash array

The simplest way to read each line of a file into a bash array is this:

IFS=$'\n' read -d '' -r -a lines < /etc/passwd

Now just index in to the array lines to retrieve each line, e.g.

printf "line 1: %s\n" "${lines[0]}"
printf "line 5: %s\n" "${lines[4]}"

# all lines
echo "${lines[@]}"

The readarray command (also spelled mapfile) was introduced in bash 4.0.

readarray -t a < /path/to/filename

Latest revision based on comment from BinaryZebra's comment and tested here. The addition of command eval allows for the expression to be kept in the present execution environment while the expressions before are only held for the duration of the eval.

Use $IFS that has no spaces\tabs, just newlines/CR

$ IFS=$'\r\n' GLOBIGNORE='*' command eval  'XYZ=($(cat /etc/passwd))'
$ echo "${XYZ[5]}"
sync:x:5:0:sync:/sbin:/bin/sync

Also note that you may be setting the array just fine but reading it wrong - be sure to use both double-quotes "" and braces {} as in the example above

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Edit:

Please note the many warnings about my answer in comments about possible glob expansion, specifically gniourf-gniourf's comments about my prior attempts to work around

With all those warnings in mind I'm still leaving this answer here (yes, bash 4 has been out for many years but I recall that some macs only 2/3 years old have pre-4 as default shell)

Other notes:

Can also follow drizzt's suggestion below and replace a forked subshell+cat with

$(</etc/passwd)

The other option I sometimes use is just set IFS into XIFS, then restore after. See also Sorpigal's answer which does not need to bother with this