Trying to embed newline in a variable in bash [duplicate]

Summary

1. Inserting \n

   p="${var1}\n${var2}"
   echo -e "${p}"
   

2. Inserting a new line in the source code

   p="${var1}
   ${var2}"
   echo "${p}"
   

3. Using $'\n' (only bash and zsh)

   p="${var1}"$'\n'"${var2}"
   echo "${p}"
   

Details

1. Inserting \n

p="${var1}\n${var2}"
echo -e "${p}"

echo -e interprets the two characters "\n" as a new line.

var="a b c"
first_loop=true
for i in $var
do
   p="$p\n$i"            # Append
   unset first_loop
done
echo -e "$p"             # Use -e

Avoid extra leading newline

var="a b c"
first_loop=1
for i in $var
do
   (( $first_loop )) &&  # "((...))" is bash specific
   p="$i"            ||  # First -> Set
   p="$p\n$i"            # After -> Append
   unset first_loop
done
echo -e "$p"             # Use -e

Using a function

embed_newline()
{
   local p="$1"
   shift
   for i in "$@"
   do
      p="$p\n$i"         # Append
   done
   echo -e "$p"          # Use -e
}

var="a b c"
p=$( embed_newline $var )  # Do not use double quotes "$var"
echo "$p"

2. Inserting a new line in the source code

var="a b c"
for i in $var
do
   p="$p
$i"       # New line directly in the source code
done
echo "$p" # Double quotes required
          # But -e not required

Avoid extra leading newline

var="a b c"
first_loop=1
for i in $var
do
   (( $first_loop )) &&  # "((...))" is bash specific
   p="$i"            ||  # First -> Set
   p="$p
$i"                      # After -> Append
   unset first_loop
done
echo "$p"                # No need -e

Using a function

embed_newline()
{
   local p="$1"
   shift
   for i in "$@"
   do
      p="$p
$i"                      # Append
   done
   echo "$p"             # No need -e
}

var="a b c"
p=$( embed_newline $var )  # Do not use double quotes "$var"
echo "$p"

3. Using $'\n' (less portable)

bash and zsh interprets $'\n' as a new line.

var="a b c"
for i in $var
do
   p="$p"$'\n'"$i"
done
echo "$p" # Double quotes required
          # But -e not required

Avoid extra leading newline

var="a b c"
first_loop=1
for i in $var
do
   (( $first_loop )) &&  # "((...))" is bash specific
   p="$i"            ||  # First -> Set
   p="$p"$'\n'"$i"       # After -> Append
   unset first_loop
done
echo "$p"                # No need -e

Using a function

embed_newline()
{
   local p="$1"
   shift
   for i in "$@"
   do
      p="$p"$'\n'"$i"    # Append
   done
   echo "$p"             # No need -e
}

var="a b c"
p=$( embed_newline $var )  # Do not use double quotes "$var"
echo "$p"

Output is the same for all

a
b
c

Special thanks to contributors of this answer: kevinf, Gordon Davisson, l0b0, Dolda2000 and tripleee.

EDIT

• See also BinaryZebra's answer providing many details.
• Abhijeet Rastogi's answer and Dimitry's answer explain how to avoid the for loop in above bash snippets.

The trivial solution is to put those newlines where you want them.

var="a
b
c"

Yes, that's an assignment wrapped over multiple lines.

However, you will need to double-quote the value when interpolating it, otherwise the shell will split it on whitespace, effectively turning each newline into a single space (and also expand any wildcards).

echo "$p"

Generally, you should double-quote all variable interpolations unless you specifically desire the behavior described above.