Ubuntu – Replace text of a specific line number using sed

command linesedtext processing

I have a html file users.html that i want to replace the first line. The first line looks like this

<template name="AccountSettings">

I want the first line to read

<template name="Users">

Best Answer

Commands in sed accept an address range. In this case, to limit the replacement to just the first line, the range should be the single address 1 i.e.

sed '1 s/AccountSettings/Users/' users.html

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Ubuntu – using Sed to search and replace text in XML file

The issue is that your search pattern contains / which you are using as the replacement delimiter, you need to use another character for that or escape the /:

sed -i 's#<!--UpdateAccountGUIDs>UpdateAndExit</UpdateAccountGUIDs-->#<UpdateAccountGUIDs>UpdateAndExit</UpdateAccountGUIDs>#' File.XML

sed -i 's/<!--UpdateAccountGUIDs>UpdateAndExit<\/UpdateAccountGUIDs-->/<UpdateAccountGUIDs>UpdateAndExit<\/UpdateAccountGUIDs>/' File.XML

Note that you should never use regular expressions to parse [X]HTML.

Finally, as a general rule, when working with regular expressions, less is more. You should try to specify the simplest possible exclusive pattern rather than repeat all text. This not only makes your code much easier to read, it also avoids problems like the one you were facing. For example:

sed -i -r 's/<!--(UpdateAccountGUIDs.+?)-->/<\1>/' File.XML

Here, the -r enables extended regular expression syntax so we can use () to capture a group (without needing to escape the parentheses) and then refer to the captured text as \1. So, the command above simply looks for a comment that is adjacent to UpdateAccountGUIDs, extends till the first end of comment statement and then does the replacement.

Ubuntu – sed replace text containing new line

How about

search for #ServerRoot "/etc/apache2"
if found, read and append the next line into sed's pattern space
search the appended pattern space for an empty line after the newline, and substitute ServerName localhost for that

Putting that together,

sed -i '\|#ServerRoot "/etc/apache2"| {N;s|\n$|\nServerName localhost|}' /etc/apache2/apache2.conf

In case the 'empty' line actually contains whitespace, you could modify that to

sed -i '\|#ServerRoot "/etc/apache2"| {N;s|\n\s*$|\nServerName localhost|}' /etc/apache2/apache2.conf

Best Answer

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Ubuntu – using Sed to search and replace text in XML file

Ubuntu – sed replace text containing new line

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