Insert multiple lines in file before specified pattern

Question

Unable to add lines before a matching line if the content has new lines and this content is generated by a function

another alternative that looked good (Insert multiple lines into a file after specified pattern using shell script) but it only appends "AFTER". I need "BEFORE"

put the xml content into add.txt then

sed '/4/r add.txt' $FILE

#/bin/sh

FILE=/tmp/sample.txt
form_xml_string()
{
  echo "<number value=\"11942\">"
  echo "  <string-attribute>\"hello\"</string-attribute>"
  echo "</number>"
}

create_file()
{
  if [ -e $FILE ]
  then
          echo "Removing file $FILE"
          rm $FILE
  fi

  i=1
  while [ $i -le 5 ]
  do
          echo "$i" >> $FILE
          i=$(( i+1 ))
   done
}

create_file
cat $FILE

# file sample.txt has numbers 1 to 5 in each line
# Now append the content from form_xml_string to line before 4
# command I tried
CONTENT=`form_xml_string`
echo "CONTENT is $CONTENT"
sed -i "/4/i $CONTENT" $FILE
cat $FILE

Expected output:

1
2
3
<number value="11942">
  <string-attribute>"hello"</string-attribute>
</number>
4
5

Actual output (or error): sed: -e expression #1, char 31: unknown command: `<'

May be I'm missing something, but `sed -i "/4/i $CONTENT" $FILE` already does what you're trying to do (insert lines BEFORE a given matching pattern)...so what's the real question here? — danrodlor, Jun 07 '19 at 09:00
Forgot to add "Actual output": This is: sed: -e expression #1, char 31: unknown command: `<' — satya, Jun 07 '19 at 09:18

Ghassen Manai · Accepted Answer · 2019-06-07T10:32:31.313

It's normal that you get that error, the syntax of your text is not compatibale with your sed command, allow me to elaborate:

First, you have a lot of /s in your text, and / is the delimiter insed, that confuses the command, which is why you get that error. So you should escape all / in the text you are using, by replacing them with \\/ (The extra \ is going to be interpreted by the shell).
Second, in the man for sed, we can see this small line about /i:

Insert text, which has each embedded newline preceded by a backslash

This means that you also need to add a \ before every newline, in your example this means adding \\ at the end of every echo.

Edit:

Thanks to Toby Speight's comment, I noticed that I forgot completly about the possiblity of changing sed's delimiter, which can make your life a lot easier, since you wouldn't have to add \\ before every / in your text. To do this all you need is to change this line sed -i "/4/i $CONTENT" $FILE to, for example, this sed -i "\\_4_i $CONTENT" $FILE.

Here's how your script will become once you introduce these changes:

#! /bin/sh
FILE=/tmp/sample.txt
form_xml_string()
{
  echo "<number value=\"11942\">\\"
  echo "  <string-attribute>\"hello\"</string-attribute>\\"
  echo "</number>"
}

create_file()
{
  if [ -e $FILE ]
  then
          echo "Removing file $FILE"
          rm $FILE
  fi

  i=1
  while [ $i -le 5 ]
  do
          echo "$i" >> $FILE
          i=$(( i+1 ))
   done
}

create_file
cat $FILE

# file sample.txt has numbers 1 to 5 in each line
# Now append the content from form_xml_string to line before 4
# command I tried
CONTENT=`form_xml_string`
echo "CONTENT is $CONTENT"
sed -i "\\_4_i $CONTENT" $FILE
cat $FILE

Might be simpler just to use a different delimiter in the sed program. — Toby Speight, Jun 07 '19 at 10:11
Btw, forgot to ask one question, How did you know to use "_" as delimiter when the default delimiter is changed. Would any other symbol have worked? — satya, Jun 07 '19 at 12:45
Yes, most symbols would be fine you could use `,` or `:` or `|` or even `#`, I chose `_` cause it's a personal preference of mine. — Ghassen Manai, Jun 07 '19 at 13:21

ceving · Answer 2 · 2019-06-07T10:36:14.677

1

Use e instead of r.

From the Sed manual about the e command:

Note that, unlike the r command, the output of the command will be printed immediately; the r command instead delays the output to the end of the current cycle.

The delay of the r command is the problem, that you can not output anything after it.

Example for the e command:

seq 0 9 | sed -e '/4/{
  h
  e cat add.xml
  g
}'

h copies the matching line into the hold space and g copies it back into the pattern space. By this it appears after the "add.xml" in the output.

edited Jun 07 '19 at 10:36

answered Jun 07 '19 at 10:30

ceving

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I liked this approach too but since the above approach (delimter change) allows me to use function and avoid file, I prefer that. Thank you for suggesting this one. – satya Jun 07 '19 at 12:41
looks like this approach wont work if write that cat line as "e cat $ADD_FILE" – satya Jun 07 '19 at 13:28
if I change sed -e ' to sed -e " ( from single quote to double quote), it works! :) – satya Jun 07 '19 at 13:30

Insert multiple lines in file before specified pattern

2 Answers2