How to use the read command in Bash?

Question

When I try to use the read command in Bash like this:

echo hello | read str
echo $str

Nothing echoed, while I think str should contain the string hello. Can anybody please help me understand this behavior?

Related: [Looping through the content of a file in Bash](https://stackoverflow.com/q/1521462/6862601) and [BashFAQ/024 - I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates?](http://mywiki.wooledge.org/BashFAQ/024). — codeforester, Oct 18 '18 at 00:01

score 63 · Accepted Answer · edited Jun 11 '17 at 18:15

63

The read in your script command is fine. However, you execute it in the pipeline, which means it is in a subshell, therefore, the variables it reads to are not visible in the parent shell. You can either

move the rest of the script in the subshell, too:
```
echo hello | { read str
  echo $str
}
```
or use command substitution to get the value of the variable out of the subshell
```
str=$(echo hello)
echo $str
```
or a slightly more complicated example (Grabbing the 2nd element of ls)
```
str=$(ls | { read a; read a; echo $a; })
echo $str
```

edited Jun 11 '17 at 18:15

Bruno

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answered Oct 06 '11 at 14:56

jpalecek

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Awesome examples! I did have to slightly tweak it on OSX by putting spaces inside the curly braces, and a semi-colon after the echo, like this: str=$(ls | { read a; read a; echo $a; }) – John Lehmann Nov 26 '12 at 19:12
@javadba: It is not required twice. The given example returns the *second* item from `ls`. With a single `read a` you would get the first item. Don't ask me why the answerer chose this example. – Fritz May 02 '17 at 11:39
To read three (or more) IFS-separated columns into variables one can do 'read VAR_1 VAR_2 VAR_3`. – Krzysztof Jabłoński Mar 02 '18 at 19:07
keeps biting me. Should be documented in the man page.. – eMPee584 Mar 20 '21 at 13:50

score 43 · Answer 2 · answered Oct 06 '11 at 15:15

43

Other bash alternatives that do not involve a subshell:

read str <<END             # here-doc
hello
END

read str <<< "hello"       # here-string

read str < <(echo hello)   # process substitution

answered Oct 06 '11 at 15:15

glenn jackman

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2

You can use a process for the here string as well such as `read A B C <<< $(echo 'aaa bbb ccc')` – maxpolk Feb 07 '17 at 15:46

score 8 · Answer 3 · answered Oct 06 '11 at 15:34

8

Typical usage might look like:

i=0
echo -e "hello1\nhello2\nhello3" | while read str ; do
    echo "$((++i)): $str"
done

and output

1: hello1
2: hello2
3: hello3

answered Oct 06 '11 at 15:34

Shizzmo

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score 3 · Answer 4 · answered Oct 06 '11 at 15:00

3

The value disappears since the read command is run in a separate subshell: Bash FAQ 24

answered Oct 06 '11 at 15:00

l0b0

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score 2 · Answer 5 · answered Apr 04 '14 at 17:36

To put my two cents here: on KSH, reading as is to a variable will work, because according to the IBM AIX documentation, KSH's read does affects the current shell environment:

The setting of shell variables by the read command affects the current shell execution environment.

This just resulted in me spending a good few minutes figuring out why a one-liner ending with read that I've used a zillion times before on AIX didn't work on Linux... it's because KSH does saves to the current environment and BASH doesn't!

score 1 · Answer 6 · edited Jul 19 '17 at 17:46

1

I really only use read with "while" and a do loop:

echo "This is NOT a test." | while read -r a b c theRest; do  
echo "$a" "$b" "$theRest"; done

This is a test.
For what it's worth, I have seen the recommendation to always use -r with the read command in bash.

edited Jul 19 '17 at 17:46

Sᴀᴍ Onᴇᴌᴀ

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answered Jul 19 '17 at 17:20

JackDR

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score 1 · Answer 7 · answered Aug 12 '21 at 11:13

1

You don't need echo to use read

 read -p "Guess a Number" NUMBER

answered Aug 12 '21 at 11:13

Ege

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score -1 · Answer 8 · answered Apr 04 '14 at 23:16

-1

Another alternative altogether is to use the printf function.

printf -v str 'hello'

Moreover, this construct, combined with the use of single quotes where appropriate, helps to avoid the multi-escape problems of subshells and other forms of interpolative quoting.

answered Apr 04 '14 at 23:16

jxqz

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If that's all you're trying to achieve, you might as well do `str='hello`. I think the point here is to capture the output of a command into a variable. – mc0e Mar 01 '16 at 03:44

score -6 · Answer 9 · answered Oct 06 '11 at 15:02

-6

Do you need the pipe?

echo -ne "$MENU"
read NUMBER

answered Oct 06 '11 at 15:02

mmrtnt

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-1: your `echo` and `read` commands are not connected in any way. – glenn jackman Oct 06 '11 at 15:16
1

The poster clearly wants an automated way to populate a variable without having to enter it manually. – glenn jackman Oct 06 '11 at 17:57

How to use the read command in Bash?

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