abc abc - 4 months ago 12
Linux Question

Trying to embed newline in a variable in bash

I have

var="a b c"
for i in $var
do
p=`echo -e $p'\n'$i`
done
echo $p


I want last echo to print

a
b
c


Notice that I want the variable p to contain newlines. How do I do that?

Answer

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 and )

    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)

and 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