read command help in bash

Question

I wanted to read output of a command in an array:

Something like:

(reformatted for code using {} above the input box)

var=`echo tell told till`
echo "$var" | while read temp; do echo $temp ; done

This program will output:

tell 
told 
till

I had two questions:

Read command reads from stdin. But in the above case how is it reading? echo puts the values on stdout.
I wanted to know how to put those elements in an array? Basically how to put elements in stdout in an array. Read -a command can put the elements in stdin, but i wanted stdout.

bash-o-logist · Accepted Answer · 2011-04-21 05:59:38Z

2

If you want to put elements from stdout into array, eg

declare -a array
array=( $(my command that generates stdout) ) #eg array=( $(ls))

If you have a variable and want to put into array

$> var="tell till told"
$> read -a array <<< $var
$> echo ${array[1]}
till
$> echo ${array[0]}
tell

OR just

array=($var)

From bash reference:

   Here Strings
       A variant of here documents, the format is:

              <<<word

       The word is expanded and supplied to the command on its standard input.

edited Apr 21, 2011 at 5:59

answered Apr 21, 2011 at 2:08

bash-o-logist

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1 Comment

Pkp Over a year ago

Tanks a ton for the soltion. It works!. Could you please tell me what is <<< symbol? I know about redirection, but its not the same. Kindly explain.

Ignacio Vazquez-Abrams · Accepted Answer · 2011-04-21 01:53:48Z

1

A pipe ("|") connects the preceding command's stdout to the following command's stdin.

answered Apr 21, 2011 at 1:53

Ignacio Vazquez-Abrams

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1 Comment

Pkp Over a year ago

Then why does'nt echo "$var" | read -a temp , store the values tell,told,till in temp array?

Jacob · Accepted Answer · 2011-04-21 02:00:15Z

1

To split a string into words you can simply use:

for word in $string;
do 
    echo $word;
done;

So to do what you're asking

while read line
do
    for word in $line
    do
        echo $word
    done
done

And as Ignacio Vazquez-Abrams said, a pipe connects the left side's stdout to the right side's stdin.

answered Apr 21, 2011 at 2:00

Jacob

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Comments

bash_fanatic · Accepted Answer · 2019-01-06 17:51:20Z

0

When you use a pipe:

command1 | command2

The output of command1, written to the stdout, will be the input for command2 (stdin). The pipe "transforms" stdout to stdin.

And for the array: You give values to the array whith:

array=(val1 val2 val3)

So just try it:

array=($var)

You've got now $var in $array:

> echo ${array[*]}
tell
told
till

> echo ${array[1]}
told

Is this what you mean?

answered Jan 6, 2019 at 17:51

bash_fanatic

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