replace a string in file using shell script

Question

Suppose my file a.conf is as following

Include /1
Include /2
Include /3

I want to replace "Include /2" with a new line, I write the code in .sh file :

line="Include /2"
rep=""
sed -e "s/${line}/${rep}/g" /root/new_scripts/a.conf

But after running the sh file, It give me the following error

sed: -e expression #1, char 14: unknown option to `s'

By editing your question to substantively change what you're asking, it is very hard to vote meaningfully on answers; indeed, the answer you accepted no longer addresses the question. Perhaps you should rollback and post a new question. — Michael J. Barber
– Michael J. Barber, Commented Dec 13, 2011 at 10:49
I thought that was my answer, but when a new criteria came, then I was bemused, sorry for that. — Pritom
– Pritom, Commented Dec 13, 2011 at 12:13
I would like to point out when you say "I want to replace "Include /2" with a new line you are in fact replacing the string with nothing. It's sed that is providing the newline once you have finished your editing. — potong
– potong, Commented Dec 13, 2011 at 12:51

Bert Regelink · Accepted Answer · 2013-05-13 13:24:01Z

21

If you are using a newer version of sed you can use -i to read from and write to the same file. Using -i you can specify a file extension so a backup will be made, incase something went wrong. Also you don't need to use the -e flag unless you are using multiple commands

sed -i.bak "s/${line}/${rep}/g" /root/new_scripts/a.conf

I have just noticed that as the variables you are using are quoted strings you may want to use single quotes around your sed expression. Also your string contains a forward slash, to avoid any errors you can use a different delimiter in your sed command (the delimiter doesn't need to be a slash):

sed -i.bak 's|${line}|${rep}|g' /root/new_scripts/a.conf

edited May 13, 2013 at 13:24

Bert Regelink

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answered Dec 13, 2011 at 9:42

luketorjussen

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3 Comments

Jon Over a year ago

I'm using shell script, and single quotes do not give the variable replacement necessary. Double quotes replaces ${rep} with the proper value.

M-D Over a year ago

This answer does not work (because of the slash character in the text). so no answer for this ?

codemonkey Over a year ago

Cheers for the pointer about being able to use a delimited other than /

eeerahul · Accepted Answer · 2011-12-13 09:52:06Z

4

You have to write the changes to a new file and then, move the new file over the old one. Like this:

line="Include 2"

rep=""

sed -e "s/${line}/${rep}/g" /root/new_scripts/a.conf > /root/new_scripts/a.conf-new

mv /root/new_scripts/a.conf-new /root/new_scripts/a.conf

edited Dec 13, 2011 at 9:52

eeerahul

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answered Dec 13, 2011 at 9:40

Ivan Dimitrov

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Comments

Eugene Yarmash · Accepted Answer · 2011-12-13 09:56:53Z

4

The redirection (> /root/new_scripts/a.conf) wipes the contents of the file before sed can see it.

You need to pass the -i option to sed to edit the file in-place:

sed -i "s/${line}/${rep}/g" /root/new_scripts/a.conf

You can also ask sed to create a backup of the original file:

sed -i.bak "s/${line}/${rep}/g" /root/new_scripts/a.conf

edited Dec 13, 2011 at 9:56

answered Dec 13, 2011 at 9:42

Eugene Yarmash

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2 Comments

Pritom Over a year ago

Hey, your answer is correct but I have a new problem now. Look at my question again.

Pritom Over a year ago

Please dont mind, if this question is mark solved then nobody answered this.

Akarsh Srivastava · Accepted Answer · 2021-02-05 09:10:12Z

1

So, if you have to replace a substring in a file, you can use sed command like this, say we have a file as file.txt, so replacing a substring in it can be done like this

searchString="abc";
replaceString="def";
sed -i '' "s|$searchString|$replaceString|g" file.txt

This will all the occurrences of "abc" with "def" in file.txt. Also, this keeps a check for any / character present in the variables used, and with no backup file made.

answered Feb 5, 2021 at 9:10

Akarsh Srivastava

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