Join Kevin Skoglund for an in-depth discussion in this video sed: Regular expressions and back-references, part of Unix for Mac OS X Users.
In the last movie, we got familiar with the syntax of sed, but all of our…searching so far has been with literal text strings.…Now we're going to learn to use regular expressions with sed.…It may seem like sed is really similar to grep.…That's because it is.…All sed is, is grep and then substitute.…So put another way, anything that you can find with grep, you can change with…sed, and that includes making good use of regular expressions.…So as a simple example of this, let's just have echo "Who needs vowels?" and…we'll pipe that into a sed expression where we will look for anything that is in…a, e, i, o, or u, inside a character set and we'll replace that with an…underscore. We'll do it globally. So there you go.…
You see it took all of the vowels that were in that character set and replaced…them with the underscore. So we can use regular expressions.…Now, the regular expressions here work exactly like they do with grep, meaning…that we also have an issue with basic versus extended regular expressions.…
- Moving around the file system
- Creating and reading files
- Copying, moving, renaming, and deleting files and directories
- Creating hard links and symbolic links
- Understanding user identity, file ownership, and sudo
- Setting file permissions with alpha and octal notation
- Changing the PATH variable
- Using the command history
- Directing input and output
- Configuring the Unix working environment
- Searching and replacing using grep and regular expressions
- Manipulating text with tr, sed, and cut
- Integrating with the Finder, Spotlight, and AppleScript
Skill Level Beginner
Q: The exercise files for the following movies appear to be broken:
Is there something wrong with them?
These exercises include one or more "dot files", whose file names start with a period. These files are normally hidden from view by the Finder. So that they would show up in the Finder, the period has been removed from the file names. Additionally, "_example" has been added at the end of the file name to make it clear that the file will not work as-is.
To make the dot files usable, either:
1) Open the file in a text editor to view its contents. Note that it may not be possible to double-click the file to open it because there is no file extension (such as .txt).
2) Resave the file under a new name (usually by choosing File > Save As), adding a "." to the beginning of the file name and removing "_example" from the end.
1) Copy and rename the file from the Unix command line using the techniques discussed in this course. Rename the file by adding a "." to the start and removing "_example" from the end. Include the "-i" option to prevent overwriting an existing file unexpectedly.
Example: cp -i ~/Desktop/Exercise\ Files/Chapter_07/07_02_files/bashrc_example ~/.bashrc
The instructor uses the UNIX program 'units' to convert 72° Fahrenheit to degrees Celsius. The returned value of 40 is incorrect. The correct result should be 22°C. What's the reason for this discrepancy?
The problem is that units does the 5/9 calculation but does not have the ability to subtract 32. So you'll need to subtract (or add) the 32 degrees yourself.
1. Introduction to Unix
2. Filesystem Basics
3. Working with Files and Directories
4. Ownership and Permissions
5. Commands and Programs
6. Directing Input and Output
7. Configuring Your Working Environment
8. Unix Power Tools
9. Useful Mac-Only Commands and Techniques
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