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Can you use sed substitution with Shell variables?
We often do text substitution using compact sed one-liners. They’re pretty convenient. However, when we execute sed substitution with shell variables, there are some pitfalls we should be aware of. In this tutorial, we’ll take a closer look at some common mistakes made using sed substitution with shell variables, and we’ll offer some solutions.
How to substitute old line for new line in SED?
I have created a second variable called new_line that is similar to old_line but with some modifications in the text. I want to substitute the contents of old_line with the contents of new_line using sed.
How to replace a string with the contents of a file?
You can read the file with the replacement string using shell command substitution, before sed is used. So sed will see just a normal substitution: I also had this “problem” today: how to replace a block of text with the contents from another file. I’ve solved it by making a bash function (that can be reused in scripts).
How to replace localhost in SED-I?
What I want to do is replace localhost with 1.1.1.1, so that the end result is: But I either get the whole line replaced, or the IP going to the line after the one I need to modify. You should use sed -i to make the change inplace. You can read the file with the replacement string using shell command substitution, before sed is used.
Which is the command for multi-line operations in SED?
sed has three commands to manage multi-line operations: N, D and P (compare them to normal n, d and p ). In this case, you can match the first line of your pattern, use N to append the second line to pattern space and then use s to do your substitution.
How can I use sed to replace a multi line string?
The hold space however is preserved. Finally, on the very last line, g restores the accumulation of every line from the hold space so that sed is able to run its regex on the whole input (rather than in a line-at-a-time fashion), and hence is able to match on s.
Can a variable be expanded within single quote in SED?
Shell variables will not get expanded within single quotes. Therefore, the quick fix would be using double quotes in the sed command to allow shell variable expansion: Now, let’s test the solution.sh script once again: Good! We’ve filled the date and time in the right place. Next, let’s fill the JAVA_HOME path in the file.