How to write multiple line string using Bash with variables?

Question

How can I write multi-lines in a file called myconfig.conf using BASH?

#!/bin/bash
kernel="2.6.39";
distro="xyz";

echo <<< EOL
line 1, ${kernel}
line 2,
line 3, ${distro}
line 4
line ...
EOL >> /etc/myconfig.conf;
cat /etc/myconfig.conf;

Answer 1

The syntax (<<<) and the command used (echo) is wrong.

Correct would be:

#!/bin/bash

kernel="2.6.39"
distro="xyz"
cat >/etc/myconfig.conf <<EOL
line 1, ${kernel}
line 2, 
line 3, ${distro}
line 4 line
... 
EOL

cat /etc/myconfig.conf

This construction is referred to as a Here Document and can be found in the Bash man pages under man --pager='less -p "\s*Here Documents"' bash.

Answer 2

The heredoc solutions are certainly the most common way to do this. Other common solutions are:

echo 'line 1, '"${kernel}"'
line 2,
line 3, '"${distro}"'
line 4' > /etc/myconfig.conf

and

exec 3>&1 # Save current stdout
exec > /etc/myconfig.conf
echo line 1, ${kernel}
echo line 2, 
echo line 3, ${distro}
...
exec 1>&3  # Restore stdout

and

printf "%s\n" "line1, ${kernel}" "line2," "line3, $distro" ...

Answer 3

#!/bin/bash
kernel="2.6.39";
distro="xyz";

cat > /etc/myconfig.conf << EOL
line 1, ${kernel}
line 2,
line 3, ${distro}
line 4
line ...
EOL

this does what you want.

Answer 4

another simpler way I think but definitely for small number of lines

touch myfile.txt
echo "line1">>myfile.txt
echo "line2">>myfile.txt
echo "line3">>myfile.txt
echo "line4">>myfile.txt

Answer 5

I usually put template in file and use this templating engine:

### <template-file> [ARG=VALUE..]
## Variables are replaced only within "{{" and "}}" notation.
## Example:
##         $0 path-to-tmpl REF=master pass=xx
##         # The template may look like so:
##         #    $pass = ["user", "{{ $pass }}"];
##         # Resulting in:
##         #    $pass = ["user", "xxx"];
##~
template() {
    tmpl=$1
    shift

    for i in $@; do
        declare $i;
    done

    eval "echo \"$(sed -e 's/"/\\"/g' -e 's/\$/\\$/g' -e 's/{{\s*\\\(\$\w*\)\s*}}/\1/g' $tmpl)\""
}

Answer 6

In my usecase I had to use the following:

{
 ...
 printf "Suites: $SUITES"
 printf "Components: $COMPONENTS"
 printf "Signed-By: $SIGNATURE"
 [ ! -z "$ARCH_STRING" ] && printf "$ARCH_STRING"
 [ ! -z "$LANG_STRING" ] && printf "$LANG_STRING"
 [ ! -z "$TARGET_STRING" ] && printf "$TARGET_STRING"
 ...
} > /tmp/myconfig.conf 

This because I did not want to write empty newlines to the file if the variables were not defined. The nice thing about this method is that you can write all kinds of arbitrary logic within the block if necessary.

And ofcourse, if you would like to append, you can also use >> here instead of > like you would in the other answers.

Answer 7

If you do not want variables to be replaced, you need to surround EOL with single quotes.

cat >/tmp/myconfig.conf <<'EOL'
line 1, ${kernel}
line 2, 
line 3, ${distro}
line 4 line
... 
EOL

Previous example:

$ cat /tmp/myconfig.conf 
line 1, ${kernel}
line 2, 
line 3, ${distro}
line 4 line
... 

Answer 8

I'm using Mac OS and to write multiple lines in a SH Script following code worked for me

#! /bin/bash
FILE_NAME="SomeRandomFile"

touch $FILE_NAME

echo """I wrote all
the  
stuff
here.
And to access a variable we can use
$FILE_NAME  

""" >> $FILE_NAME

cat $FILE_NAME

Please don't forget to assign chmod as required to the script file. I have used

chmod u+x myScriptFile.sh

Answer 9

Below mechanism helps in redirecting multiple lines to file. Keep complete string under " so that we can redirect values of the variable.

#!/bin/bash
kernel="2.6.39"
echo "line 1, ${kernel}
line 2," > a.txt
echo 'line 2, ${kernel}
line 2,' > b.txt

Content of a.txt is

line 1, 2.6.39
line 2,

Content of b.txt is

line 2, ${kernel}
line 2,