UNIX and Linux sed

This tutorial is meant as a brief introductory guide to sed that will help give the beginner a solid foundation regarding how sed works. It's worth noting that the tutorial also omits several commands, and will not bring you to sed enlightenment in itself. To reach sed enlightenment, your best bet is to follow the seders mailing list. to do that , send email to Al Aab

Prerequisites

It is assumed that the reader is familiar with regular expressions. If this is not the case, read the grep tutorial which includes information on regular expressions. On this page, we just give a brief revision.

Sed regular expressions

The sed regular expressions are essentially the same as the grep regular expressions. They are summarized below.

^ matches the beginning of the line

$ matches the end of the line

. Matches any single character

For Sed - An Introduction and Tutorial by Bruce Barnett

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Sed - stream editor

The Single UNIX ® Specification, Version 2

Copyright © 1997 The Open Group

NAME
sed - stream editor

SYNOPSIS
sed [-n] script[file...]
sed [-n][-e script]...[-f script_file]...[file...]

DESCRIPTION
The sed utility is a stream editor that reads one or more text files, makes editing changes according to a script of editing commands, and writes the results to standard output. The script is obtained from either the script operand string or a combination of the option-arguments from the -e script and -f script_file options.

OPTIONS
The sed utility supports the XBD specification, Utility Syntax Guidelines , except that the order of presentation of the -e and -f options is significant.

The following options are supported:

-e script
Add the editing commands specified by the script option-argument to the end of the script of editing commands. The script option-argument has the same properties as the script operand, described in the OPERANDS section.

-f script_file
Add the editing commands in the file script_file to the end of the script.

-n
Suppress the default output (in which each line, after it is examined for editing, is written to standard output). Only lines explicitly selected for output will be written.

Multiple -e and -f options may be specified. All commands are added to the script in the order specified, regardless of their origin.

OPERANDS
The following operands are supported:

file
A pathname of a file whose contents will be read and edited. If multiple file operands are specified, the named files will be read in the order specified and the concatenation will be edited. If no file operands are specified, the standard input will be used.

script
A string to be used as the script of editing commands. The application must not present a script that violates the restrictions of a text file except that the final character need not be a newline character.

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Sed by example, Part 3

Get to know the powerful UNIX editor

By Daniel Robbins

In this conclusion of the sed series, Daniel Robbins gives you a true taste of the power of sed. After introducing a handful of essential sed scripts, he'll demonstrate some radical sed scripting by converting a Quicken .QIF file into a text-readable format. This conversion script is not only functional, it also serves as an excellent example of sed scripting power.

Muscular sed
In my second sed article, I offered examples that demonstrated how sed works, but very few of these examples actually did anything particularly useful. In this final sed article, it's time to change that pattern and put sed to good use. I'll show you several excellent examples that not only demonstrate the power of sed, but also do some really neat (and handy) things. For example, in the second half of the article, I'll show you how I designed a sed script that converts a .QIF file from Intuit's Quicken financial program into a nicely formatted text file. Before doing that, we'll take a look at some less complicated yet useful sed scripts.

Text translation
Our first practical script converts UNIX-style text to DOS/Windows format. As you probably know, DOS/Windows-based text files have a CR (carriage return) and LF (line feed) at the end of each line, while UNIX text has only a line feed. There may be times when you need to move some UNIX text to a Windows system, and this script will perform the necessary format conversion for you.

$ sed -e 's/$/\r/' myunix.txt > mydos.txt

In this script, the '$' regular expression will match the end of the line, and the '\r' tells sed to insert a carriage return right before it. Insert a carriage return before a line feed, and presto, a CR/LF ends each line. Please note that the '\r' will be replaced with a CR only when using GNU sed 3.02.80 or later. If you haven't installed GNU sed 3.02.80 yet, see my first sed article for instructions on how to do this.

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Sed by example, Part 2

Get to know the powerful UNIX editor

By Daniel Robbins

Sed is a very powerful and compact text stream editor. In this article, the second in the series, Daniel shows you how to use sed to perform string substitution; create larger sed scripts; and use sed's append, insert, and change line commands

Sed is a very useful (but often forgotten) UNIX stream editor. It's ideal for batch-editing files or for creating shell scripts to modify existing files in powerful ways. This article builds on my previous article introducing sed.

Substitution!
Let's look at one of sed's most useful commands, the substitution command. Using it, we can replace a particular string or matched regular expression with another string. Here's an example of the most basic use of this command:

$ sed -e 's/foo/bar/' myfile.txt

The above command will output the contents of myfile.txt to stdout, with the first occurrence of 'foo' (if any) on each line replaced with the string 'bar'. Please note that I said first occurrence on each line, though this is normally not what you want. Normally, when I do a string replacement, I want to perform it globally. That is, I want to replace all occurrences on every line, as follows:

$ sed -e 's/foo/bar/g' myfile.txt

The additional 'g' option after the last slash tells sed to perform a global replace.

Here are a few other things you should know about the 's///' substitution command. First, it is a command, and a command only; there are no addresses specified in any of the above examples. This means that the 's///' command can also be used with addresses to control what lines it will be applied to, as follows:

$ sed -e '1,10s/enchantment/entrapment/g' myfile2.txt

The above example will cause all occurrences of the phrase 'enchantment' to be replaced with the phrase 'entrapment', but only on lines one through ten, inclusive.

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Sed by example, Part 1

Get to know the powerful UNIX editor

By Daniel Robbins

In this series of articles, Daniel Robbins will show you how to use the very powerful (but often forgotten) UNIX stream editor, sed. Sed is an ideal tool for batch-editing files or for creating shell scripts to modify existing files in powerful ways.

In the UNIX world, we have a lot of options when it comes to editing files. Think of it -- vi, emacs, and jed come to mind, as well as many others. We all have our favorite editor (along with our favorite keybindings) that we have come to know and love. With our trusty editor, we are ready to tackle any number of UNIX-related administration or programming tasks with ease.
While interactive editors are great, they do have limitations. Though their interactive nature can be a strength, it can also be a weakness. Consider a situation where you need to perform similar types of changes on a group of files. You could instinctively fire up your favorite editor and perform a bunch of mundane, repetitive, and time-consuming edits by hand. But there's a better way.

Enter sed
It would be nice if we could automate the process of making edits to files, so that we could "batch" edit files, or even write scripts with the ability to perform sophisticated changes to existing files. Fortunately for us, for these types of situations, there is a better way -- and the better way is called "sed".

sed is a lightweight stream editor that's included with nearly all UNIX flavors, including Linux. sed has a lot of nice features. First of all, it's very lightweight, typically many times smaller than your favorite scripting language. Secondly, because sed is a stream editor, it can perform edits to data it receives from stdin, such as from a pipeline. So, you don't need to have the data to be edited stored in a file on disk. Because data can just as easily be piped to sed, it's very easy to use sed as part of a long, complex pipeline in a powerful shell script. Try doing that with your favorite editor.

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