Styjun

UPDATED#2

Explanation is in Blue Moons's answer.

Alternative solutions:

Eliminate echo

while read line; do
...
done <<EOT
first line
second line
third line
EOT

Add the echo inside the here-is-the-document

while read line; do
...
done <<EOT
$(echo -e $lines)
EOT

Run echo in background:

coproc echo -e $lines
while read -u $COPROC[0] line; do 
...
done

Redirect to a file handle explicitly (Mind the space in < <!):

exec 3< <(echo -e $lines)
while read -u 3 line; do
...
done

Or just redirect to the stdin:

while read line; do
...
done < <(echo -e $lines)

And one for chepner (eliminating echo):

arr=("first line" "second line" "third line");
for((i=0;i<$#arr[*];++i)) line=$arr[i]; 
...

Variable $lines can be converted to an array without starting a new sub-shell. The characters and n has to be converted to some character (e.g. a real new line character) and use the IFS (Internal Field Separator) variable to split the string into array elements. This can be done like:

lines="first linensecond linenthird line"
echo "$lines"
OIFS="$IFS"
IFS=$'n' arr=($lines//\n/$'n') # Conversion
IFS="$OIFS"
echo "$arr[@]", Length: $#arr[*]
set|grep ^arr

Result is

first linensecond linenthird line
first line second line third line, Length: 3
arr=([0]="first line" [1]="second line" [2]="third line")

You are the 742342nd user to ask this bash FAQ. The answer also describes the general case of variables set in subshells created by pipes:

E4) If I pipe the output of a command into read variable, why
doesn't the output show up in $variable when the read command finishes?

This has to do with the parent-child relationship between Unix
processes. It affects all commands run in pipelines, not just
simple calls to read. For example, piping a command's output
into a while loop that repeatedly calls read will result in
the same behavior.

Each element of a pipeline, even a builtin or shell function,
runs in a separate process, a child of the shell running the
pipeline. A subprocess cannot affect its parent's environment.
When the read command sets the variable to the input, that
variable is set only in the subshell, not the parent shell. When
the subshell exits, the value of the variable is lost.

Many pipelines that end with read variable can be converted
into command substitutions, which will capture the output of
a specified command. The output can then be assigned to a
variable:

grep ^gnu /usr/lib/news/active | wc -l | read ngroup

can be converted into

ngroup=$(grep ^gnu /usr/lib/news/active | wc -l)

This does not, unfortunately, work to split the text among
multiple variables, as read does when given multiple variable
arguments. If you need to do this, you can either use the
command substitution above to read the output into a variable
and chop up the variable using the bash pattern removal
expansion operators or use some variant of the following
approach.

Say /usr/local/bin/ipaddr is the following shell script:

#! /bin/sh
host `hostname` | awk '/address/ print $NF'

Instead of using

/usr/local/bin/ipaddr | read A B C D

to break the local machine's IP address into separate octets, use

OIFS="$IFS"
IFS=.
set -- $(/usr/local/bin/ipaddr)
IFS="$OIFS"
A="$1" B="$2" C="$3" D="$4"

Beware, however, that this will change the shell's positional
parameters. If you need them, you should save them before doing
this.

This is the general approach -- in most cases you will not need to
set $IFS to a different value.

Some other user-supplied alternatives include:

read A B C D << HERE
 $(IFS=.; echo $(/usr/local/bin/ipaddr))
HERE

and, where process substitution is available,

read A B C D < <(IFS=.; echo $(/usr/local/bin/ipaddr))

Hmmm... I would almost swear that this worked for the original Bourne shell, but don't have access to a running copy just now to check.

There is, however, a very trivial workaround to the problem.

Change the first line of the script from:

#!/bin/bash

to

#!/bin/ksh

Et voila! A read at the end of a pipeline works just fine, assuming you have the Korn shell installed.

This is an interesting question and touch a very basic concept in Bourne shell and subshell. Here I provide a solution that is different from the previous solutions by doing some kind of filtering. I will give an example that may be useful in real life. This is a fragment for checking the downloaded files conform to know checksums. The checksum file look like the following (Showing just 3 lines):

49174 36326 dna_align_feature.txt.gz
54757 1 dna.txt.gz
55409 9971 exon_transcript.txt.gz

The shell script:

#!/bin/sh

.....

failcnt=0 # this variable is only valid in the parent shell
#variable xx captures all the outputs from the while loop
xx=$(cat $checkfile | while read -r line; do
 num1=$(echo $line | awk 'print $1')
 num2=$(echo $line | awk 'print $2')
 fname=$(echo $line | awk 'print $3')
 if [ -f "$fname" ]; then
 res=$(sum $fname)
 filegood=$(sum $fname | awk -v na=$num1 -v nb=$num2 -v fn=$fname ' if (na == $1 && nb == $2) print "TRUE"; else print "FALSE"; ')
 if [ "$filegood" = "FALSE" ]; then
 failcnt=$(expr $failcnt + 1) # only in subshell
 echo "$fname BAD $failcnt"
 fi
 fi
done | tail -1) # I am only interested in the final result
# you can capture a whole bunch of texts and do further filtering
failcnt=$xx#* BAD # I am only interested in the number
# this variable is in the parent shell
echo failcnt $failcnt
if [ $failcnt -gt 0 ]; then
 echo $failcnt files failed
else
 echo download successful
fi

The parent and subshell communicate through the echo command. You can pick some easy to parse text for the parent shell. This method does not break your normal way of thinking, just that you have to do some post processing. You can use grep, sed, awk, and more for doing so.

How about a very simple method

 +call your while loop in a function 
 - set your value inside (nonsense, but shows the example)
 - return your value inside 
 +capture your value outside
 +set outside
 +display outside


 #!/bin/bash
 # set -e
 # set -u
 # No idea why you need this, not using here

 foo=0
 bar="hello"

 if [[ "$bar" == "hello" ]]
 then
 foo=1
 echo "Setting $foo to $foo"
 fi

 echo "Variable $foo after if statement: $foo"

 lines="first linensecond linenthird line"

 function my_while_loop
 

 echo -e $lines 

 my_while_loop; foo="$?"

 echo "Variable $foo after while loop: $foo"


 Output:
 Setting $foo 1
 Variable $foo after if statement: 1
 Value of $foo in while loop body: 1
 Variable $foo after while loop: 2

 bash --version

 GNU bash, version 3.2.51(1)-release (x86_64-apple-darwin13)
 Copyright (C) 2007 Free Software Foundation, Inc.