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Accepted
ChrisInCambo
Asked: 2009-10-09 02:54:00 +0800 CST

Clean way to write complex multi-line string to a variable

  • 772

I need to write some complex xml to a variable inside a bash script. The xml needs to be readable inside the bash script as this is where the xml fragment will live, it's not being read from another file or source.

So my question is this if I have a long string which I want to be human readable inside my bash script what is the best way to go about it?

Ideally I want:

  • to not have to escape any of the characters
  • have it break across multiple lines making it human readable
  • keep it's indentation

Can this be done with EOF or something, could anyone give me an example?

e.g.

String = <<EOF
 <?xml version="1.0" encoding='UTF-8'?>
 <painting>
   <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
   <caption>This is Raphael's "Foligno" Madonna, painted in
   <date>1511</date>-<date>1512</date>.</caption>
 </painting>
EOF
bash

5 Answers

  1. Best Answer

    This will put your text into your variable without needing to escape the quotes. It will also handle unbalanced quotes (apostrophes, i.e. '). Putting quotes around the sentinel (EOF) prevents the text from undergoing parameter expansion. The -d'' causes it to read multiple lines (ignore newlines). read is a Bash built-in so it doesn't require calling an external command such as cat.

    IFS='' read -r -d '' String <<"EOF"
<?xml version="1.0" encoding='UTF-8'?>
 <painting>
   <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
   <caption>This is Raphael's "Foligno" Madonna, painted in
   <date>1511</date>-<date>1512</date>.</caption>
 </painting>
EOF
    • 161

  2. You've been almost there. Either you use cat for the assembly of your string or you quote the whole string (in which case you'd have to escape the quotes inside your string):

    #!/bin/sh
VAR1=$(cat <<EOF
<?xml version="1.0" encoding='UTF-8'?>
<painting>
  <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
  <caption>This is Raphael's "Foligno" Madonna, painted in
  <date>1511</date>-<date>1512</date>.</caption>
</painting>
EOF
)

VAR2="<?xml version=\"1.0\" encoding='UTF-8'?>
<painting>
  <img src=\"madonna.jpg\" alt='Foligno Madonna, by Raphael'/>
  <caption>This is Raphael's \"Foligno\" Madonna, painted in
  <date>1511</date>-<date>1512</date>.</caption>
</painting>"

echo "${VAR1}"
echo "${VAR2}"
    • 38 
  3. #!/bin/sh

VAR1=`cat <<EOF
<?xml version="1.0" encoding='UTF-8'?>
<painting>
  <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
  <caption>This is Raphael's "Foligno" Madonna, painted in
  <date>1511</date>-<date>1512</date>.</caption>
</painting>
EOF
`
echo "VAR1: ${VAR1}"

    This should work fine within Bourne shell environment

    • 18

  4. Yet another way to do the same...

    I like to use variables and special <<- who drop tabulation at begin of each lines to permit script indentation:

    #!/bin/bash

mapfile Pattern <<-eof
        <?xml version="1.0" encoding='UTF-8'?>
        <painting>
          <img src="%s" alt='%s'/>
          <caption>%s, painted in
          <date>%s</date>-<date>%s</date>.</caption>
        </painting>
        eof

while IFS=";" read file alt caption start end ;do
    printf "${Pattern[*]}" "$file" "$alt" "$caption" "$start" "$end"
  done <<-eof
        madonna.jpg;Foligno Madonna, by Raphael;This is Raphael's "Foligno" Madonna;1511;1512
        eof

    warning: there is no blank space before eof but only tabulation.

    <?xml version="1.0" encoding='UTF-8'?>
 <painting>
   <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
   <caption>This is Raphael's "Foligno" Madonna, painted in
   <date>1511</date>-<date>1512</date>.</caption>
 </painting>
    Some explanations:
    • mapfile read entire here document in an array.
    • the syntaxe "${Pattern[*]}" do cast this array into a string.
    • I use IFS=";" because there is no ; in required strings
    • The syntaxe while IFS=";" read file ... prevent IFS to be modified for the rest of the script. In this, only read do use the modified IFS.
    • no fork.
    • 6

  5. There are too many corner cases in many of the other answers.

    To be absolutely sure there are no issues with spaces, tabs, IFS etc., a better approach is to use the "heredoc" construct, but encode the contents of the heredoc using uuencode as explained here:

    https://stackoverflow.com/questions/6896025/#11379627.

    • 2