How do I read multiple lines from STDIN into a variable?

Question

I've been googling this question to no avail. I'm automating a build process here at work, and all I'm trying to do is get version numbers and a tiny description of the build which may be multi-line. The system this runs on is OSX 10.6.8.

I've seen everything from using CAT to processing each line as necessary. I can't figure out what I should use and why.

Attempts

read -d '' versionNotes

Results in garbled input if the user has to use the backspace key. Also there's no good way to terminate the input as ^D doesn't terminate and ^C just exits the process.

read -d 'END' versionNotes

Works... but still garbles the input if the backspace key is needed.

while read versionNotes
do
  echo "  $versionNotes" >> "source/application.yml"
done

Doesn't properly end the input (because I'm too late to look up matching against an empty string).

Correct; I want the user to enter this information in the terminal when executing the script. — Robert K, Apr 10 '12 at 11:22

poige · Answer 1 · 2018-10-05T02:58:34.410

35

man bash mentions «…

The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

…»

$ myVar=$(</dev/stdin)
hello
this is test
$ echo $myVar
hello this is test
$ echo "$myVar"
hello
this is test

and I agree this is worth mentioning — echo "$myVar" would have displayed the input as it was given.

edited Oct 05 '18 at 02:58

answered Jun 11 '12 at 10:29

poige

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1

How to stop after multiline input? If I press Ctrl C it stops but the variable is not saved! – Porcupine Aug 13 '18 at 09:46
2

UNIX® terminals do have "discipline": https://en.wikipedia.org/wiki/Line_discipline • Check it out what does "eof" mean • Do read `man stty`, find out how to get current settings – poige Aug 13 '18 at 15:43
3

ctrl-d to stop. – freb Oct 23 '18 at 02:52
A complement from [this answer](https://stackoverflow.com/a/42866846/1879269), if you want to write directly into a file, simply use ```echo "$( /tmp/file```. – Lalylulelo Mar 21 '23 at 10:19

voices · Answer 2 · 2017-03-24T12:04:48.540

22

Try this:

user@host:~$ read -d '' x <<EOF
> mic
> check
> one
> two
> EOF

Without line breaks:

user@host:~$ echo $x
mic check one two

With line breaks:

user@host:~$ echo "$x"
mic
check
one
two

edited Mar 24 '17 at 12:04

answered Jun 12 '16 at 18:34

voices

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`-d ''` is exactly what I needed. Thanks – Bruno Bronosky Mar 09 '17 at 22:53
@Bruno My pleasure; it's a tricky one. Especially at first glance, it looks fairly standard. Can be quite useful though, once you get the hang of the various idiosyncrasies. – voices Mar 11 '17 at 08:57

score 8 · Answer 3 · answered Apr 25 '12 at 13:17

8

Refer to the excellent Bash Guide for all your bash scripting needs.

In particular the Bash FAQ contains this at number #1:

How can I read a file (data stream, variable) line-by-line (and/or field-by-field)?

answered Apr 25 '12 at 13:17

adaptr

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You say to use `read -r`, but how do I get it to do so from STDIN? I did attempt to use `read -r` early on. – Robert K Apr 25 '12 at 17:17
It reads from stdin by default. – adaptr Apr 26 '12 at 07:17

score 3 · Answer 4 · answered Apr 25 '12 at 13:23

3

You can start an editor like vim, pico...

${VISUAL:-${EDITOR:-vi}} source/application.yml

answered Apr 25 '12 at 13:23

Mircea Vutcovici

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Um... how does that answer the OP's question in any way ? – adaptr Apr 25 '12 at 13:27
He can start the editor from the script. – Mircea Vutcovici Apr 25 '12 at 14:46
1

And that accomplishes what, exactly ? He wants to use text *from* a file in the script, not write information *to* a file. – adaptr Apr 25 '12 at 15:05
He wasnts to read text from the user and write it to a file. Please read the comments added to the question. – Mircea Vutcovici Apr 25 '12 at 16:03

score 2 · Answer 5 · answered Apr 25 '12 at 13:13

2

I've solved this issue by dealing with each line until I came up with a blank line. It works well enough for my situation. But if someone wants to add a better solution, feel free to do so.

echo "---
notes: |" > 'version.yml'

while read line
do
  # break if the line is empty
  [ -z "$line" ] && break
  echo "  $line" >> "source/application.yml"
done

answered Apr 25 '12 at 13:13

Robert K

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Use `read -r` instead. – adaptr Apr 25 '12 at 13:26

score 1 · Answer 6 · answered Dec 30 '21 at 13:29

As in your comment you are stating that the input comes from a user via terminal: You can use read to read multi line input via

read -d $'\04' versionNotes

which sets the delimiter to EOF, which is 0x04 in unicode so you can read input until CTRL-D is given.

score 1 · Answer 7 · edited Mar 23 '18 at 07:24

First a few corrections:

To allow "edition" on the line use -e which uses readline (so you have the bash history and all editing features)
-d only takes one character. E.g. from 'END' takes 'E' and whenever the user writes an 'E' the reading stops (I guess that's not what you want...)

There are a few possibilities to do this. I'd go for read line by line and stop when an empty line is found (though you could set any stop word):

unset tmp
while :
do 
 read line
 [[ $line == "" ]] && tmp="${tmp:0:$((${#tmp}-1))}" && break
 tmp="$tmp"$line$'\n'
done

JamesIsIn · Answer 8 · 2020-02-05T11:41:36.710

We are using a construct using xargs and ctrl-d for breaking. I'm not perfectly satisfied with it, but it certainly does the job of taking multi-line user input and stuffing that into a variable (formatting intact). (The first and third assignments add quotes around the contents of the xargs input.)

    printf '%s\n' "When finished hit ctrl-d on a new line to proceed.  " "" "" 
    # this will load the user's input into a variable instead of a file 
    reminderBody="\"" 
    reminderBody+=$( xargs -0 ) 
    reminderBody+="\""

We use reminderBody as the body of an e-mail being sent by mail (via bash).

score 0 · Answer 9 · edited Mar 23 '18 at 02:24

0

You have several methods.

One of the simplest methods is:

MYVAR=$(yourcommand)
echo $"MYVAR"

For example:

MYVAR=$(ls /)
echo $"MYVAR"

edited Mar 23 '18 at 02:24

Andrew Schulman

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answered Apr 09 '12 at 22:15

Bertrand SCHITS

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Except I'm not executing a shell command like LS. I'm requesting multi-line input from the user. – Robert K Apr 10 '12 at 11:23
This is very bad practice; do not process the output of `ls`! – adaptr Apr 25 '12 at 13:14
@adaptr We've heard it all before, would you mind suggesting a good alternative, please? – voices Mar 11 '17 at 08:50

score -1 · Answer 10 · edited Mar 23 '18 at 12:40

-1

See: http://tldp.org/LDP/abs/html/internal.html#READR

Use read and note that if you end a line with \ the newline is ignored. So you could do:

#!/bin/bash

read -p "version: " version
echo $version

# enter some input and end long lines with "\", then plain enter at the end
read -p "description: " description
echo -e "$version\n$description >> yourfile.txt

edited Mar 23 '18 at 12:40

wjandrea

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answered Apr 24 '12 at 21:18

Kindjal

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If I just wanted a paragraph with line breaks ignored, yes. But as this is a generated list of release notes for a build script, I need to be able to preserve those line breaks; I might try to enter a bulleted list, for example. – Robert K Apr 25 '12 at 13:09
The ABS is a monstrosity of horrific proportions. 90% of it is plain wrong. – adaptr Apr 25 '12 at 13:26
It's not *that* bad. – voices Mar 11 '17 at 08:45

How do I read multiple lines from STDIN into a variable?

Attempts

10 Answers10