Shell Scripting, 'sed' usage, String substitution in a file

Question

I know this question has probably been answered before. I have seen many threads about this in various places, but the answers are not working for me. I am looking for help with an example usage of the 'sed' command.

What I am trying to do is reading some strings from a file and then using those values to replace the strings of few other files

Example:

File1.txt

name:
abcd

age:
22

File2.xml

<root>
 <name>xxxx</name>
 <age>xxxx</age>
</root>

I am reading name and age from file 1 and trying to replace missing values in the file 2. I have tried to use hard coding and replacing the values in a file :

$name=abcd
$age=22

sed -e 's/.*<name>\([^<]*\)</name>.*/${name}/g' file2.xml

Note: it is not possible to use sed -i. Old version I guess

for the above script I am getting an error

sed: 0602-404 Function s/.*<name>\([^<]*\)</name>.*/${name}/g cannot be parsed.

so first of all I'd like a script to read from the file and then a script to write in to a file without creating a new file.

UPDATE :

for the below added $ mark

$ sed -e 's/.*<name>\([^<]*\)</name>.*/${name}/g' file2.xml

I am getting error./test.sh: line 4: $: command not found

Which sed are you using? Show output of sed --version. What does sed --help say for using -i?Please quote the relevant part of --help. What other influence does the age of your servers have on seds handling of -i? — Yunnosch
– Yunnosch, Commented Jun 15, 2017 at 6:20
@Yunnosch i am using an GNU Bash, version 4.2.50. I am unable to get an output for sed --version or sed --help — Hasith
– Hasith, Commented Jun 15, 2017 at 6:25
How are you executing the sed scripts you are working on or asking about? — Yunnosch
– Yunnosch, Commented Jun 15, 2017 at 6:30
I am saving it as myScript.sh file and then execute in bash as ./myScript.sh. hope that makes sense — Hasith
– Hasith, Commented Jun 15, 2017 at 6:37
Please type into your bash commandline sed --version. What is the output? Otherwise replace inside your script the existing sed line with sed --version, then execute the script and show the output. — Yunnosch
– Yunnosch, Commented Jun 15, 2017 at 6:39

Weike · Accepted Answer · 2017-06-15 06:36:26Z

1

First, you need "" instead of '' to fetch the value of a variable. And, you should use capture group instead.

$ sed -r -e "s|(.*<name>)[^<]+(</name>)|\1${name}\2|g" -e "s|(.*<age>)[^<]+(</age>)|\1${age}\2|g" File2.txt
<root>
 <name>abcd</name>
 <age>22</age>
</root>

Or just put ${name} outside of the '':

$ sed -r -e 's|(.*<name>)[^<]+(</name>)|\1'${name}'\2|g' -e 's|(.*<age>)[^<]+(</age>)|\1'${age}'\2|g' File2.txt
<root>
 <name>abcd</name>
 <age>22</age>
</root>

PS: maybe can don't have the write permission for File2.txt, so you can NOT use -i.bak

edited Jun 15, 2017 at 6:36

answered Jun 15, 2017 at 6:30

Weike

1,27012 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Hasith Over a year ago

I think I have the write permissions since I created both files.

CWLiu · Accepted Answer · 2017-06-15 06:56:58Z

0

You may choose to use awk, it's a more straightforward method.

Use the command:

awk 'NR==FNR{
  if(match($0,/name/)){getline;name=$0}
  if(match($0,/age/)){getline;age=$0}
  next}
  /<name>/{gsub(/>.*</,">"name"<",$0)}
  /<age>/{gsub(/>.*</,">"age"<",$0)}
  {print}
' File1.txt File2.xml

Output:

<root>
 <name>abcd</name>
 <age>22</age>
</root>

Brief explanation:

match(): extract the name & age from File1.txt
gsub(): to substitute name & age in File2.xml

edited Jun 15, 2017 at 6:56

answered Jun 15, 2017 at 6:44

CWLiu

4,0531 gold badge13 silver badges14 bronze badges

6 Comments

Hasith Over a year ago

Thanks I will try it. :)

Hasith Over a year ago

How can I run awk in Bash ? Same as shell scripting. like ./myScript.sh ? would work for awk too?

CWLiu Over a year ago

Hi, no more file would be added in this way. @Hasith, just paste the command to your bash environment should be okay.

Hasith Over a year ago

I added the code in to a shellscript and executed it to see it print the output as i wanted to see, but it doesn't change the config.xml as I wanted.

CWLiu Over a year ago

@Hasith, awk did not modify the original file actually. But you may follow stackoverflow.com/questions/37795186/… to overwrite the file, a tmp file is required.

|

Collectives™ on Stack Overflow

Shell Scripting, 'sed' usage, String substitution in a file

2 Answers 2

1 Comment

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related