SED
https://www.grymoire.com/Unix/Sed.html
Last modified: Tue Jul 25 11:54:15 2023
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Table of Contents Note - You can click on the table of contents sections to jump to that section. And if you click on a section header, it returns you to the Table of Contents. Handy, eh?
The Awful Truth about sed The essential command: s for substitution The slash as a delimiter Using & as the matched string Using 1 to keep part of the pattern Extended Regular Expressions Sed Pattern Flags /g - Global replacement Is sed recursive? /1, /2, etc. Specifying which occurrence /p - print Write to a file with /w filename /I - Ignore Case Combining substitution flags Arguments and invocation of sed Multiple commands with -e command Filenames on the command line sed -n: no printing Using ‘sed /pattern/’ Using ‘sed -n /pattern/p’ to duplicate the function of grep sed -f scriptname sed in shell scripts Quoting multiple sed lines in the C shell Quoting multiple sed lines in the Bourne shell sed -V sed -h A sed interpreter script Sed Comments Passing arguments into a sed script Using sed in a shell here-is document Multiple commands and order of execution Addresses and Ranges of Text Restricting to a line number Patterns Ranges by line number Ranges by patterns Delete with d Printing with p Reversing the restriction with ! Relationships between d, p, and ! The q or quit command Grouping with { and } Operating in a pattern range except for the patterns Writing a file with the ‘w’ command Reading in a file with the ‘r’ command The # Comment Command Adding, Changing, Inserting new lines Append a line with ‘a’ Insert a line with ‘i’ Change a line with ‘c’ Leading tabs and spaces in a sed script Adding more than one line Adding lines and the pattern space Address ranges and the above commands Multi-Line Patterns Print line number with = Transform with y Displaying control characters with a l Working with Multiple Lines Matching three lines with sed Matching patterns that span multiple lines Using newlines in sed scripts The Hold Buffer Exchange with x Example of Context Grep Hold with h or H Keeping more than one line in the hold buffer Get with g or G Branch (Flow Control) Testing with t Debugging with l An alternate way of adding comments The poorly documented ; Passing regular expressions as arguments Inserting binary characters GNU sed Command Line arguments The -posix argument The –version argument The -h Help argument The -l Line Length Argument The -s Separate argument The -i in-place argument The –follow-symlinks argument The -b Binary argument The -r Extended Regular Expression argument The -u Unbuffered argument The -z Null Data argument FreeBSD Extensions -a or delayed open The -I in-place argument -E or Extended Regular Expressions Using word boundaries Command Summary In Conclusion More References Introduction to Sed How to use sed, a special editor for modifying files automatically. If you want to write a program to make changes in a file, sed is the tool to use.
There are a few programs that are the real workhorse in the UNIX toolbox. These programs are simple to use for simple applications, yet have a rich set of commands for performing complex actions. Don’t let the complex potential of a program keep you from making use of the simpler aspects. I’ll start with the simple concepts and introduce the advanced topics later on. When I first wrote this (in 1994), most versions of sed did not allow you to place comments inside the script. Lines starting with the ‘#’ characters are comments. Newer versions of sed may support comments at the end of the line as well.
One way to think of this is that the old, “classic” version was the basis of GNU, FreeBSD and Solaris versions of sed. And to help you understand what I had to work with, here is the sed(1) manual page from Sun/Oracle.
The Awful Truth about sed Sed is the ultimate stream editor. If that sounds strange, picture a stream flowing through a pipe. Okay, you can’t see a stream if it’s inside a pipe. That’s what I get for attempting a flowing analogy. You want literature, read James Joyce.
Anyhow, sed is a marvelous utility. Unfortunately, most people never learn its real power. The language is very simple, but the documentation is terrible. The Solaris on-line manual pages for sed are five pages long, and two of those pages describe the 34 different errors you can get. A program that spends as much space documenting the errors as it does documenting the language has a serious learning curve.
Do not fret! It is not your fault you don’t understand sed. I will cover sed completely. But I will describe the features in the order that I learned them. I didn’t learn everything at once. You don’t need to either.
And remember, clicking on a section title brings you back to the Table Of Contents. Click on the entry in the Table of contents brings you back to that section! Try it now!
c02
The sed command, short for stream editor, performs editing operations on text coming from standard input or a file. sed edits line-by-line and in a non-interactive way.
This means that you make all of the editing decisions as you are calling the command, and sed executes the directions automatically. This may seem confusing or unintuitive, but it is a very powerful and fast way to transform text, especially as part of a script or automated workflow.
This tutorial will cover some basic operations and introduce you to the syntax required to operate this editor. You will almost certainly never replace your regular text editor with sed, but it will probably become a welcomed addition to your text editing toolbox.
Note: This tutorial uses the GNU version of sed found on Ubuntu and other Linux operating systems. If you’re using macOS, you’ll have the BSD version which has different options and arguments. You can install the GNU version of sed with Homebrew using brew install gnu-sed.
c03 –
https://thevaluable.dev/sed-cli-practical-guide-examples/
The sun is shining today; too bad, you’re stuck in the office of your beloved company, MegaCorpMoneyMaker. Your task is to delete specific lines across thousands of XML files; it’s the “API” of an external warehouse, and, as always, they screwed it up.
You begin to write a script using your favorite programming language, when suddenly Davina, your colleague developer, comes to your desk:
“You know that you don’t have to write a script to do that? You could simply use sed in your terminal.”
You used sed in the past, but only to substitute some words with others. How could Davina delete specific lines depending on their content? You don’t have time to think more: Davina is already on your keyboard.
“It’s super easy. I’ll show you!”
Curious to learn more, you let her explain what sed is all about. This article is the transcription of this magical day which changed the world.
More specifically, Davina explained the following:
What argument we can give to sed. What’s a sed script. How to write the input file in place. How to use an address in a sed script to edit specific lines. How to use the commands print and delete. How to invert the address. How to use more than one command in a sed script. How to use the substitute command. As the title suggest, we’ll focus on GNU sed in this article. If you don’t have it, I’d recommend you to install and use it. To know if you have GNU sed, simply run sed –version in your shell; if it doesn’t work, you don’t have it. If it does work, you’ll get the information you seek.
Also, if you prefer watching videos instead of reading, you’ll find two at the end of this article, recorded by your humble servant.
Last thing: you can download the companion file if you want to follow along and try by yourself the different commands. I’d recommend you to do so, to remember what we’ll see here, and be able to use sed in different contexts.
It’s time! Get your diving gear and let’s explore the intricate caves of our stream of text.
The Basics of sed Let’s begin by the obvious: what on Earth does “sed” mean? This lovely name is for stream editor. It’s indeed an editor which follows this workflow:
Take a stream of text as input. Select some specific lines. Perform some operations on each line selected. Output the resulting text. The second and third steps are done thanks to a sed script. We’ll look at this concept later; first, let’s look at what arguments we can give to sed in our shell.