Is it possible to echo into a file, but use indenting in the shell script source?

Question

If I have some nested and indented statements that echo a multi-line string into a file, the indents from the original shell (in my case bash) will be carried over into the target file.

To avoid this, I remove indents from the echo'ed output, but this loses that indented code formatting in my source, for example,

#! /bin/bash

function configure_default_vhost() {

    case "$2" in
        [--production])
              echo "<VirtualHost *:80>
# These lines are "breaking" out of the preffered indenting
redirect 404 /
ErrorDocument 404
</VirtualHost>
" > /etc/apache/sites-availabe/000-default.conf
    esac
}

I'm aiming to get something as close as possible to this:

#! /bin/bash

function configure_default_vhost() {

    case "$2" in
        [--production])
              echo "<VirtualHost *:80>
                    # These lines are aligned with the preffered indenting
                    redirect 404 /
                    ErrorDocument 404
                    </VirtualHost>
                    " > /etc/apache/sites-availabe/000-default.conf
    esac
}

_{(Note: this question has been listed as a possible duplicate of a HEREDOC related question. I'm not sure where the correct place to respond to this is so I'll put here for now (someone please let know if otherwise). My question is about indenting code blocks, and heredoc is only one of the many ways to acheive this and actually HEREDOC wasn't the solution I went with.)}

Answer 1

You can use a "here-document" with the - modifier. It can be indented by tab characters. You must switch from echo to cat.

cat <<-EOF > /etc/apache/sites-availabe/000-default.conf
        <VirtualHost *:80>
        redirect 404 /
        ErrorDocument 404     
        </VirtualHost>
EOF

Or, to keep tabs in the result, you can pre-process the HERE document by let's say sed and indent with 4 spaces instead:

sed 's/^    //' <<EOF
....{
....(------)func () {
....(------)return
....(------)}
....}
EOF

I used . instead of a space and (------) instead of a tab to show how to format the script.

Answer 2

A few approaches:

• printf '%s\n' > "$conf_file" \
    '<VirtualHost *:80>' \
    '  redirect 404 /' \
    '  ErrorDocument 404' \
    '</VirtualHost>'
  

  If you want escape sequences to be expanded replace %s with %b:

  printf '%b\n' > "$conf_file" \
    '<VirtualHost *:80>' \
    '\tredirect 404 /' \
    '\tErrorDocument 404' \
    '</VirtualHost>'
  

• @choroba's cat <<- EOF approach, but indentation has to be done with TAB characters only and they're all removed.

• ...
    indent='
    '; cut -b "${#indent}-" << EOF > "$conf_file"
    <VirtualHost *:80>
      redirect 404 /
      ErrorDocument 404     
    </VirtualHost>
  EOF
  

  (the trick being to have $indent hold the number of characters of indent to trim (beware this time, indenting has to be done with space characters, not tabs)).

• ...
    cut -d'|' -f2- << EOF > "$conf_file"
    |echo "<VirtualHost *:80>
    |  redirect 404 /
    |  ErrorDocument 404     
    |</VirtualHost>
  EOF
  

  Escape sequences won't be expanded, but variables and command substitutions will. Quote EOF to prevent that (cut... << 'EOF' for instance).

• You can also trim indentation based on that of the first line:

  show() {
    expand | awk 'NR == 1 {match($0, /^ */); l = RLENGTH + 1}
                  {print substr($0, l)}'
  }
  ...
    show << EOF > "$conf_file"
      <VirtualHost *:80>
        redirect 404 /
        ErrorDocument 404     
      </VirtualHost>
  EOF
  

Answer 3

Using echo with the -e switch ( enable the interpretation of backslash escapes):

#!/bin/bash

function configure_default_vhost() {
    conf_file="/etc/apache/sites-availabe/000-default.conf"
    case "$2" in
        [--production])
            # The ">" overwrites; the ">>" appends. 
            {
                echo -e "<VirtualHost *:80>"
                echo -e "\tredirect 404 /"
                echo -e "\tErrorDocument 404"
                echo -e "</VirtualHost>"
            } > "$conf_file"
    esac
}