100

If there's a "First World Problems" for scripting, this would be it.

I have the following code in a script I'm updating:

if [ $diffLines -eq 1 ]; then
        dateLastChanged=$(stat --format '%y' /.bbdata | awk '{print $1" "$2}' | sed 's/\.[0-9]*//g')

        mailx -r "Systems and Operations <sysadmin@[redacted].edu>" -s "Warning Stale BB Data" jadavis6@[redacted].edu <<EOI
        Last Change: $dateLastChanged

        This is an automated warning of stale data for the UNC-G Blackboard Snapshot process.
EOI

else
        echo "$diffLines have changed"
fi

The script sends email without issues, but the mailx command is nested within an if statement so I appear to be left with two choices:

  1. Put EOI on a new line and break indentation patterns or
  2. Keep with indentation but use something like an echo statement to get mailx to suck up my email.

I'm open to alternatives to heredoc, but if there's a way to get around this it's my preferred syntax.

2
  • 3
    Very First World! Sep 4, 2021 at 3:34
  • It’s very rare that you need to combine awk and sed in the same command.  Here. you could do stat … | awk '{sub(/\.[0-9]*/, ""); print $1, $2}', thus doing the substitution in awk and eliminating the sed.  (Use gsub if there is a possibility of multiple occurrences of the pattern.) Mar 24 at 18:32

8 Answers 8

163

You can change the here-doc operator to <<-. You can then indent both the here-doc and the delimiter with tabs:

#! /bin/bash
cat <<-EOF
    indented
    EOF
echo Done

Note that you must use tabs, not spaces to indent the here-doc. This means the above example won't work copied (Stack Exchange replaces tabs with spaces). There can not be any quotes around the first EOF delimiter, else parameter expansion, command substitution, and arithmetic expansion are not in effect.

8
  • 2
    @JoelDavis: Just remove the quotes, keep the hyphen.
    – choroba
    May 20, 2013 at 18:37
  • 17
    Being forced to use tabs is very annoying. Is there a good way around it?
    – con-f-use
    Nov 19, 2015 at 18:25
  • 3
    @con-f-use: You can try something like cat << EOF | sed 's/^ *//' and so on.
    – choroba
    Nov 19, 2015 at 19:33
  • 7
    Or even better: cat <<- EOF | awk 'NR==1 && match($0, /^ +/){n=RLENGTH} {print substr($0, n+1)}'. This removes the amount of preceding spaces in the first line from every line in the here document (thanks to anubhava).
    – con-f-use
    Nov 21, 2015 at 10:40
  • 1
    Actually, the only line that needs a <Tab> is the final "EOF" line. The rest of the lines can use spaces. (at least in Bash v4... not sure of earlier.)
    – Cometsong
    Feb 12, 2018 at 18:29
18

If you don't need command substitution and parameter expansion inside your here-document, you can avoid using tabs by adding the leading spaces to the delimiter:

$     cat << '    EOF'
>         indented
>     EOF
        indented
$     cat << '    EOF' | sed -r 's/^ {8}//'
>         unindented
>     EOF
unindented

I couldn't figure out a way to use this trick and keep parameter expansion, though.

1
  • 2
    To me, this is the only answer which solves the indenting problem without using spaces. shell-check will find any indent changes which con't match the spaces in the quoted string. Use double quotes for parameter expansion?
    – Tom Hale
    Jun 26, 2018 at 17:18
6

Try this:

sed 's/^ *//' >> ~/Desktop/text.txt << EOF
    Load time-out reached and nothing to resume.
    $(date +%T) - Transmission-daemon exiting.
EOF
1
  • 1
    You can't have differently-indented lines within the heredoc is this case. (This matters if e.g. the contents is a script.) Aug 8, 2019 at 9:45
2

The other method would be herestrings:

    mail_content="Last Change: $dateLastChanged

    This is an automated warning of stale data for the UNC-G Blackboard Snapshot process."
    mailx -r "Systems and Operations <sysadmin@[redacted].edu>" -s "Warning Stale BB Data" jadavis6@[redacted].edu <<<"$mail_content"
0
1

Hmm... Seems like you could take better advantage of the --format argument here to use --printf instead and just pass the lot over a pipe. Also, your if...fi is a compound command - it can take a redirect which all contained commands will inherit, so maybe you don't need to nest the heredoc at all.

if      [ "$diffLines" = 1 ]
then    stat --printf "Last Change: %.19y\n\n$(cat)\n" /.bbdata |
        mailx   -r  "Systems and Operations <sysadmin@[redacted].edu>" \
                -s  "Warning Stale BB Data" 'jadavis6@[redacted].edu'
else    echo    "$diffLines have changed"
fi      <<\STALE
This is an automated warning of stale data for the UNC-G Blackboard Snapshot process.
STALE
6
  • Yeah my previous revision said I didn't mind the sed/awk part. Part of my revision today was to take it out since it wasn't germane to the question. Either way it's six of one half a dozen of the other.
    – Bratchley
    Jan 27, 2015 at 16:27
  • @Bratchley - damn. That last sentence is going to distract me for the rest of the day.
    – mikeserv
    Jan 27, 2015 at 16:28
  • How do you mean?
    – Bratchley
    Jan 27, 2015 at 16:29
  • 1
    @Bratchley - Looks like a riddle.
    – mikeserv
    Jan 27, 2015 at 16:30
  • Ha. Not sure what country you're from but that's a common phrase in the States. Just means "Different approach to the same end." Your solution does get around heredoc though.
    – Bratchley
    Jan 27, 2015 at 16:31
1

You could use a here-string (<<<) instead of a here-document (<<MARKER), which at least avoids the end-of-document marker not being intended.

if [[ true ]]; then
  # Sample indented block
  cat <<<'First line
  Second line
  '
fi

Output (note the trailing empty line):

First line
  Second line
  

You can combine this with other commands to strip indent. Here cut will output the fifth character onwards of each line. -c is character mode, and 5- is the range of characters to output.

if [[ true ]]; then
  # Sample indented block
  cut -c5- <<<'
    First line
    Second line
  '
fi

Output (note first and last line are empty):


First line
Second line

Excellent explanation of the difference at command line - What's the difference between <<, <<< and < < in bash? - Ask Ubuntu.

0

This answer is GNU-Bash-specific.

The trick is that we use the <<< one-word here-doc offered by Bash, and we make that a multi-line item.

We also avoid a UUoC: we don't need a cat process to feed input to sed:

$ sed '1d;s/^    //' <<<"
    {
       TERM=$TERM
    }
    bye"

Output shows leading four-space indentation removed, and $TERM expanded:

{
   TERM=xterm-256color
}
bye

the 1d command in sed is to delete the first blank line, which exists because our quoted literal starts with a newline after the opening quote.

Of course, in the real script for which this is indented—pardon me, intendeded—we would line up the braces with the sed command, which would be indented inside a loop or conditional.

If we start each line of the datum with a delimiter, then a simple sed substitution will delete a variable amount of indentation, so that the block can be freely moved around between indentation levels:

while command ; do
    if condition ; then
        variable=$(sed '1d;s/^.*|//' <<<"
                  |{
                  |   TERM=$TERM
                  |}
                  |bye
                  ")
    fi
done

One last idea is to put the indent magic into a variable which is used as a sort of macro:

# put in some common definitions library section
indent='sed 1d;s/^.*|//'

# ...

while command ; do
    if condition ; then
        variable=$($indent <<<"
                  |{
                  |   TERM=$TERM
                  |}
                  |bye
                  ")
    fi
done

We can improve this by writing a good old-fashioned function:

# put in some common definitions library section
ind()
{
   sed '1d;s/^.*|//' <<<$1
}

# ...

while command ; do
    if condition ; then
        variable=$(ind "
                  |{
                  |   TERM=$TERM
                  |}
                  |bye
                  ")
    fi
done

Then we have abstracted away the <<< entirely.

0

Given that this is an aesthetic issue, here's an aesthetic solution: place some visual aid into the code which acts as a transition between the "proper" pre-heredoc indentation and temporary left-alignment of the heredoc block.

if [ $condition -eq 1 ]; then
              ︙
       some code
       some more code

# ____/

mailx -r "Systems and Operations <sysadmin@[redacted].edu>" -s "Warning Stale BB Data" jadavis6@[redacted].edu <<EOI
Last Change: $dateLastChanged

This is an automated warning of stale data for the UNC-G Blackboard Snapshot process.
EOI

# ____
#     \

       even more code
              ︙
else
        code
          ︙
fi

I find that this allows my brain to better perceive the left-aligned code as part of the indented code around it. When I'm writing in a code editor that indicates the level of indentation with a vertical line, the above visual aid appears to merge into the indicator for the previous indent level, making the transition feel even more intuitive. Not everyone will find this satisfying, of course, but there don't seem to be any universally satisfying answers for when you have space-indented code.

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