How can I replace a string using sed?

Question

I am trying to use sed to replace a string with another one. I used the below command and it worked just fine up until I ran cat index.html and it went back to the old string. Can someone help, please?

<h1>
Hello World
</h1>
<p>This is out first WebDev study</p>
</body>
</html>
$ sed 's/Hello World/About Us/' index.html
<!DOCTYPE>
<html>
<head>
<link rel="stylesheet" href="style.css">
</head>
<body>
<h1>
About Us
</h1>
<p>This is out first WebDav study</p>
</body>
</html>
$ cat index.html
<!DOCTYPE>
<html>
<head>
<link rel="stylesheet" href="style.css">
</head>
<body>
<h1>
Hello World
</h1>
<p>This is out first WebDav study</p>
</body>
</html>

sed by default writes the modified file to standard output - see How can I get my sed command to make permanent changes to a file? for how to write the modified content back to the input file (aka "in-place" editing) — steeldriver, Aug 11 '21 at 23:14
Also note that while sed can work for extremely simple cases like this, you really should use a HTML parser if you want to extract or modify HTML files (this typically means using another language, like perl or python, or a tool like xmlstarlet if your html is valid xhtml). e.g. your sed script would fail if there was a linefeed or more than one space (or a  between Hello and World (but would still render exactly the same in a browser. sed is a line-oriented tool, it does not deal well with structured text. HTML is not a line-oriented format, it is structured text. — cas, Aug 12 '21 at 07:24
Does this answer your question? How can I get my sed command to make permanent changes to a file? — G-Man Says 'Reinstate Monica', May 15 '22 at 18:33

score 2 · Accepted Answer · answered Aug 12 '21 at 00:15

2

From the man page:

-i[SUFFIX], --in-place[=SUFFIX]
     edit files in place (makes backup if SUFFIX is supplied)

So, in your case you just need to add the flag:

sed -i 's/Hello World/About Us/' index.html

answered Aug 12 '21 at 00:15

user1794469

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How can I replace a string using sed?

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