Sed - An Introduction and Tutorial
This is the Grymoire's UNIX/Linux SED editor. Using 'sed -n /pattern/p' to duplicate the function of grep Relationships between d, p, and! The substitute command changes all occurrences of the regular expression into a. Download FAR - Find And Replace for free. Search and replace operations on file content accross multiple files. Recursive operations within. You can check if your Linux system has emacs installed by simply running the following command: emacs . The mini buffer shows the prompt for the text to be searched (Query replace:). Type the . Search files using grep.
This area is called the mini buffer. Emacs is a command driven tool and the mini buffer is your main point of interaction with emacs. This is where emacs prompts you for command inputs or shows you the output. Windows The text-based version of emacs treats "windows" quite differently from its GUI-based version.
Unlike GUI-based applications, text-based emacs windows don't just pop out, they can't physically do so in a terminal or console session. Instead, when emacs needs to start a new window, its main buffer is split into two parts, like having two frames in a browser. The top half shows the main buffer and the bottom half displays the new content. An example of emacs spawning a new window is when you are accessing its help files or tutorials.
We will talk more about windows later. Basic Command Keys Now that we are familiar with the user interface, it may be tempting to start typing and messing around.
Just before we do so, let's spend a few more minutes on emacs' command keys. Like most things in Linux, emacs relies heavily on keyboard commands. Fortunately, most of these keystrokes are fairly standard and easy to remember. Also, unlike vi, emacs doesn't have to switch between editing and command modes.
When you open a file with emacs, you can just start typing and issue commands at the same time.
Command functions in emacs usually involve two or three keys. The most common is the Ctrl key, followed by the Alt or Esc key. In emacs literature, Ctrl is shown in short form as "C". So if you see something like C-x C-c, it means "press the Ctrl key and x together, then press Ctrl and c".
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Similarly, if you see C-h t, it means "press Ctrl and h together, then release both keys and press t". Alt and Esc keys are referred to as "meta" key in emacs lingo. In Mac machines that's the Option key and in some keyboards it's labelled as Edit. That's why emacs documentations show these keys as "M" M for meta. Just like the Ctrl key, emacs uses multi-key functions with the meta key. The Esc key usually plays its part when you try to back off from a command or prompt. Just keep pressing it till you get out of trouble.
Saving and Quitting Once you have made some changes to your document or written some text, you would want to save it. The mini buffer will show a message like this: If there is unsaved data, the mini-buffer will show a prompt like this: Modified buffers exist; exit anyway? This would take you back to command prompt.
Navigation Basics Navigating through a long document or help topic can be a tedious task if you don't know the right keys. Fortunately, in emacs there are not too many of these to remember and they are quite intuitive. Here is a list: Basic Editing Functions We will now learn about some basic editing functions in emacs.
Let's start with the simple task of selecting text.
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Marking Text Regions To mark a text region similar to selecting text in popular word processorsfollow these steps: Move the cursor to the position where you would like the selection to start. You can use any of the methods described before to move the cursor. The mini buffer will show a status message of Mark set. Move the cursor to the position where you want the region to end.
Again, use any of the key combinations described before. The text will be highlighted up to the point where your cursor is now located. If you want to "un-mark" the highlighted text, press C-Space or C- twice.
The mini buffer will show a status message of Mark deactivated. Here is an example of marked text: If you want to select the all the contents of the main buffer i. Pressing M-h will select the current paragraph. For copying the text, press E-w For cutting the text, press C-w Move your cursor to the position where the text needs to be pasted.
Press C-y y stands for "yank" - you are yanking the text from one position to another. The contents will be pasted here. Deleting Text For deleting, Backspace and Delete keys work just the way you would expect them to work. For deleting a whole word, move the cursor at the beginning of a word and press M-d. For deleting multiple words, hold the meta key down and keep pressing d. Words will start deleting one by one. For deleting a whole line, position the cursor where you want it to be and press C-k.
This would delete the text right up to the end of the line on screen. For deleting a sentence, press M-k. Just so that we know, emacs considers a sentence to have completed when it sees two spaces after the full stop.
This is unlike traditional publishing where a new sentence begins after a single space following a full stop. That's how emacs is smart enough to know even when a sentence has broken across multiple lines. You can keep repeating this to go backwards. Another way to do the same thing would be to press C-x C-u again Undoing the Undo.
In forward search, the word you specify will be searched forward from the current cursor position. For backward search, it's the other way round. Press C-s for forward search Press C-r for backward search The mini-buffer will display a prompt like I-search: As soon as you start typing, emacs will try to search for the text being typed and highlight any matches it finds in the main buffer. Here is an example. The next screenshot shows we are trying to search for the word "cat". Note how every occurrence in the main buffer is highlighted.
For replacing text, follow these steps: The mini buffer shows the prompt for the text to be searched Query replace: Type the replacing text and press Enter.
You can take any of the following actions: Press y to replace the current match found. Press n to skip to the next match. At the top of each directory panel there are small arrows circled in the image below.
Clicking on them will show the directory history the up arrow and move forward and backward through the history list the right and left arrows. There is also an arrow to the extreme lower right edge of the command line which reveals the command line history. Directory and command line history mouse controls Viewing and Editing Files An activity often performed while directory browsing is examining the content of files.
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Midnight Commander provides a capable file viewer which can be accessed by selecting a file and pressing the F3 key. File viewer As we can see, when the file viewer is active, the function key labels at the bottom of the screen change to reveal viewer features. Files can be searched and the viewer can quickly go to any position in the file. Most importantly, files can be viewed in either ASCII regular text or hexadecimal, for those cases when we need a really detailed view.
File viewer in hexadecimal mode It is also possible to put the other panel into "quick view" mode to view the the currently selected file. This is especially nice if we are browsing a directory full of text files and want to rapidly view the files, as each time a new file is selected in the current panel, it's instantly displayed in the other.
To start quick view mode, type Ctrl-x q. Quick view mode Once in quick view mode, we can press Tab and the focus changes to the other panel in quick view mode.
This will change the function key labels to a subset of the full file viewer. To exit the quick view mode, press Tab to return to the directory panel and press Alt-i. Editing Since we are already viewing files, we will probably want to start editing them too.
Midnight Commander accommodates us with the F4 key, which invokes a text editor loaded with the selected file. Midnight Commander can work with the editor of your choice. On Debian-based systems we are prompted to make a selection the first time we press F4. Debian suggests nano as the default selection, but various flavors of vim are also available along with Midnight Commander's own built-in editor, mcedit.
We can try out mcedit on its own at the command line for a taste of this editor. After all, we can perform those kinds of operations more easily by entering commands directly on the command line.
However, we often want to operate on multiple files. This can be accomplished through tagging. When a file is tagged, it is marked for some later operation such as copying. This is why we choose to use a file manager like Midnight Commander. When one or more files are tagged, file operations such as copying are performed on the tagged files and selection has no effect. Tagging Individual Files To tag an individual file or directory, select it and press the Insert key.
To un-tag it, press the Insert key again. This will display a dialog where the pattern may be specified. File tagging dialog This dialog stores a history of patterns. To traverse it, use Ctrl up and down arrows. It is also possible to un-tag a group of files. Creating Directories The first step in creating a playground is creating a directory called, aptly enough, playground.
First, we will navigate to our home directory, then press the F7 key. Create Directory dialog Type "playground" into the dialog and press Enter. Next, we want the other panel to display the contents of the playground directory.
To do this, highlight the playground directory and press Alt-o. Now let's put some files into our playground. Press Tab to switch the current panel to the playground directory panel. We'll create a couple of subdirectories by repeating what we did to create playground.
Create subdirectories dir1 and dir2. Finally, using the command line, we will create a few files: Select dir1, then press Alt-o to display dir1 in the other panel. We are now presented with this formidable-looking dialog box: Copy dialog To see Midnight Commander's default behavior, just press Enter and file1 is copied into directory dir1 i. That was straightforward, but what if we want to copy file2 to a file in dir1 named file3? To do this, we select file2 and press F5 again and enter the new filename into the Copy dialog: Renaming a file during copy Again, this is pretty straightforward.
But let's say we tagged a group of files and wanted to copy and rename them as they are copied or moved. How would we do that? Midnight Commander provides a way of doing it, but it's a little strange. The secret is the source mask in the copy dialog. At first glance, it appears that the source mask is simply a file selection wildcard, but first appearances can be deceiving.
The mask does filter files as we would expect, but only in a limited way. Unlike the range of wildcards available in the shell, the wildcards in the source mask are limited to "? What's more, the wildcards have a special property. It works like this: This wildcard pattern will match the file ugly file, since its name consists of two strings of characters separated by a space. Midnight Commander will associate each block of text with a number starting with 1, so block 1 will contain "ugly" and block 2 will contain "file".
Each block can be referred to by a number as with regular expression grouping. Using grouping The "?
If we make the source mask "???? Midnight Commander can also perform case conversion on file names. To do this, we include some additional escape sequences in the to mask: Creating Links Midnight Commander can create both hard and symbolic links. They are created using these 3 keyboard commands which cause a dialog to appear where the details of the link can be specified: Ctrl-x l creates a hard link, in the directory shown in the current panel.
Ctrl-x s creates a symbolic link in the directory shown in the other panel, using an absolute directory path. Ctrl-x v creates a symbolic link in the directory shown in the other panel, using a relative directory path. The two symbolic link commands are basically the same. They differ only in the fact that the paths suggested in the Symbolic Link dialog are absolute or relative. We'll demonstrate creating a symbolic link by creating a link to file1.
To do this, we select file1 in the current panel and type Ctrl-x s. The Symbolic Link dialog appears and we can either enter a name for the link or we can accept the program's suggestion. For the sake of clarity, we will change the name to file1-sym. Doing so will display a dialog box in which each attribute can be turned on or off. If Midnight Commander is being run with superuser privileges, file ownership can be changed by typing Ctrl-x o. Chmod dialog To demonstrate changing file modes, we will make file1 executable.
First, we will select file1 and then type Ctrl-x c. The Chmod command dialog will appear, listing the file's mode settings.
Deleting Files Pressing the F8 key deletes the selected or tagged files and directories. By default, Midnight Commander always prompts the user for confirmation before deletion is performed. We're done with our playground for now, so it's time to clean up. We will enter cd at the shell prompt to get the current panel to list our home directory.
Next, we will select playground and press F8 to delete the playground directory. Delete confirmation dialog Power Features Beyond basic file manipulation, Midnight Commander offers a number of additional features, some of which are very interesting. Virtual File Systems Midnight Commander can treat some types of archive files and remote hosts as though they are local file systems.05 Manipulating output with grep, awk, and cut
Using the cd command at the shell prompt, we can access these. For example, we can look at the contents of tar files. We can do this by entering this command at the shell prompt: If we select this file and press Enter, the contents of the archive will be displayed in the current panel.
Notice that the shell prompt does not change as it does with ordinary directories. This is because while the current panel is displaying a list of files like before, Midnight Commander cannot treat the virtual file system in the same way as a real one.
For example, we cannot delete files from the tar archive, but we can copy files from the archive to the real file system. Virtual file systems can also treat remote file systems as local directories. Its name is ftp. The FISH protocol is similar. This protocol can be used to communicate with any Unix-like system that runs a secure shell SSH server.
If we have write permissions on the remote server, we can operate on the remote system's files as if they were local. This is extremely handy for performing remote administration.
The cd command for FISH protocol looks like this: When invoked by pressing Alt-? Find dialog On this dialog we can specify: This feature is well-suited to searching large trees of source code or configuration files for specific patterns of text.
To do this, we would fill in the dialog as follows: