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Table of Contents
SED
sed is a stream editor used to perform basic text transformations on an input stream (a file or input from a pipeline).
sed takes one or more editing commands and applies all of them, in sequence, to each line of input.
After all the commands have been applied to the first input line, that line is output and a second input line is taken for processing, and the cycle repeats.
Typical Usage
| Example Usage | Comment |
|---|---|
| cat filename | sed '10q' | Uses piped input. |
| sed '10q' filename | Same effect, avoids a useless “cat”. |
| sed '10q' filename > newfile | Redirects output to disk. |
Quoting Syntax
The preceding examples use single quotes ('…') instead of double quotes (“…”) to enclose editing commands, since sed is typically used on a Unix platform.
Single quotes prevent the Unix shell from interpreting the dollar sign ($) and back-quotes (`…`), which are expanded by the shell if they are enclosed in double quotes.
Users of the “csh” shell and derivatives will also need to quote the exclamation mark (!) with the backslash (i.e., \!) to properly run the examples listed above, even within single quotes.
Versions of sed written for DOS invariably require double quotes (“…”) instead of single quotes to enclose editing commands.