Unix – Set Multi-Line Text To A String Variable Or Text File in Bash

There are many ways to save a multi line string in bash.
This is post just shows how to output a multiline string.

The Basics – Quoting Variables

From the bash(1) man page:

If any characters in word are quoted,
the delimiter is the result of quote removal on word,
and the lines in the here-document are not expanded.

Also single quotes(e.g. ‘EOF’) or double quotes(e.g. “EOF”) can be used as stop tokens
The minus trims leading spaces or blanks. The quotes around the token prevent variable expansion inside document.

Examples

i. heredoc with variable expansion

cat > myfile.txt < myfile.txt <
ii. heredoc without variable expansion
cat > myfile.txt <<"EOF"
this file has $variable $dollar $name $inside
EOF

#print out the content of myfile.txt
cat myfile.txt
#this file has $variable $dollar $name $inside



The quoted "EOF" directive is determines whether or not variable name inside the multi line string will be expanded.
iii. heredoc without variable expansion - example 2
cat > myfile.txt <
Escaping dollar inside a heredoc string is error prone and should be avoided!

So option ii. is the best
1. Set Multi Line Text to a String Variable

read -d '' stringvar <<-"_EOF_"

all the leading dollars in the $variable $name are $retained

_EOF_

echo $stringvar;
# all the leading dollars in the $variable $name are $retained



2. Set Multi Line Text to a String Variable
read -d '' help <<- "_EOF_"
  usage: up [--level | -n ][--help][--version]

  Report bugs to:
  up home page:
_EOF_



3. Set Multi Line Text to a String Variable

VARIABLE1="

  
  Thus is a future post on Multi Line Strings in bash
  1511-1512.
"


4. Set Multi Line Text to a String Variable
VARIABLE2=$(cat <

  
  Thus is a future post on Multi Line Strings in bash
  1511-1512.

EOF
)

5. Set Multi Line Text to a String Variable
VARABLE3=`cat <

  
  Thus is a future post on Multi Line Strings in bash
  1511-1512.

EOF`

6. Save A Multi Line String to a Text File
cat > heredocfile.txt <<_EOF_
I am line 1
I am line 2
I'm the last line
_EOF_

Test File Contents
cat heredocfile.txt

# and then, change your echo statement to include the '-e' option
# which will turn on escape sequence processing:
echo -e $USAGE >&2

7. Save A Multi Line String to a Text File
this redirect does not work ...
sudo cat > /aaaa.txt <<_EOF_
I am line 1
I am line 2
I'm the last line
_EOF_

# sudo and >>: permission denied
# Fix below

8. Save A Multi Line String to a Text File
# create
sudo tee /aaa.txt << EOF
  echo "Hello World 20314"
EOF

9. Append a Multi Line String to a Text File
# Append to Sudo
sudo tee -a  /aaa.txt << EOF
 echo "This Line is appended"
EOF

10. Save Multi Line String to a Text File


sudo sh -c "cat > /aaa.txt" <<"EOT"
this text gets saved as sudo - $10 - ten dollars ...
EOT

cat /aaa.txt
#this text gets saved as sudo - $10 - ten dollars ...


11. Save Multi Line String to a Text File

cat << "EOF" | sudo tee /aaa.txt
let's count
$one
two
$three
four

EOF

cat /aaa.txt
#let's count
#$one
#two
#$three
#four


tee --help
> tee --help
Usage: tee [OPTION]... [FILE]...
Copy standard input to each FILE, and also to standard output.

  -a, --append              append to the given FILEs, do not overwrite
  -i, --ignore-interrupts   ignore interrupt signals
      --help     display this help and exit
      --version  output version information and exit

If a FILE is -, copy again to standard output.

Report tee bugs to bug-coreutils@gnu.org
GNU coreutils home page: 
General help using GNU software: 
For complete documentation, run: info coreutils 'tee invocation'


References
1. Heredoc Quoting - Credit to Ignacio Vazquez-Abrams: http://serverfault.com/questions/399428/how-do-you-escape-characters-in-heredoc

2. eredoc Quoting - Credit to Dennis Williamson: http://stackoverflow.com/questions/3731513/how-do-you-type-a-tab-in-a-bash-here-document

3. http://serverfault.com/questions/72476/clean-way-to-write-complex-multi-line-string-to-a-variable

4. http://arstechnica.com/civis/viewtopic.php?p=21091503

5. http://superuser.com/questions/201829/sudo-permission-denied

6. http://stackoverflow.com/questions/4937792/using-variables-inside-a-bash-heredoc

7. http://stackoverflow.com/questions/2600783/how-does-the-vim-write-with-sudo-trick-work

8. http://www.unix.com/shell-programming-scripting/187477-variables-heredoc.html