This will tell the OS to find the 'text to find' in every file in every directory, all the way down through the tree. The -r flag tells grep to recursively search directories. Of course, OS X has something like 26,000 files, so this can take a very long time! The optional second parameter pos gives an index in the string where the search is to start; it defaults to 0. This is not completely equivalent to slicing the string; the '^' pattern character matches at the real beginning of the string and at positions just after a newline, but not necessarily at the index where the search is to start. Jan 02, 2015 Others have offered flexible suggestions to find the 2nd, 3rd, 4th etc occurrence but if your requirement is only to look up the 2nd occurrence, then you could use either of these non array-entered formulas.
program'. If that doesn't help, it's probably because you're wondering what a regular expression ('re' or 'regex') is. Basically, it's a pattern used to describe a string of characters, and if you want to know aaaaaaall about them, I highly
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recommend reading Mastering Regular Expressions by Jeffrey Friedl and published by Unix 端ber-publisher O'Reilly & Associates.
Regexes (regices, regexen, ...the pluralization is a matter of debate) are an extremely useful tool for any kind of text processing. Searching for patterns with grep is most people's first exposure to them, as like the article says, you can use them to search for a literal pattern within any number of text files on your computer. The cool thing is that it doesn't have to be a literal pattern, but can be as complex as you'd like.
The key to this is understanding that certain characters are 'metacharacters', which have special meaning for the regex-using program. For example, a plus character (+) tells the program to match one or more instances of whatever immediately precedes it, while parentheses serve to treat whatever is contained as a unit. Thus, 'ha+' matches 'ha', but it also matches 'haa' and 'haaaaaaaaaaa', but not 'hahaha'. If you want to match the word 'ha', you can use '(ha)+' to match one or more instances of it, such as 'hahaha' and 'hahahahahahahahaha'. Using a vertical bar allows alternate matching, so '(ha|ho)+' matches 'hohoho', 'hahaha', and 'hahohahohohohaha'. Etc.
There are many of these metacharacters to keep in mind. Inside brackets ([]), a carat (^) means that you don't want to match whatever follows inside the brackets. For Magritte fans, '[^(a cigar)]' matches any text that is not 'a cigar'. The rest of the time, the carat tells the program to match only at the beginning of a line, while a dollar sign ($) matches only at the end. Therefore, '^everything$' matches the word 'everything' only when it is on a line all by itself and '^[^(anything else)]' matches all lines that do not begin with 'anything else'.
The period (.) matches any character at all, and the asterisk (*) matches zero or more times. Compare this to the plus, which matches one or more times -- a subtle but important difference. A lot of regular expressions look for '.*', which is zero or more of anything (that is, anything at all). This is useful when searching for two things that might or might not have anything else (that you probably don't care about) between them: 'foo.*bar' will match on 'foobar', 'foo bar' & 'foo boo a wop bop a lop bam boo bar'. Changing the previous example to a plus, 'foo.+bar', requires that anything -- come between foo and bar, but it doesn't matter what, so 'foobar' doesn't match but the other two examples given do match.
For details, try the man pages -- 'man grep'. There are a lot of different versions of the program, so details may vary. All of this should be valid for OSX though.
Confusing? Maybe, but regular expressions aren't that bad when you get used to them, and they can be a very useful tool to take advantage of it you know what you're doing. An example.
Let's say you have an website stored on your computer as a series of html documents. As a cutting edge developer, you've seen the CSS light and want to delete all the tags wherever they're just saying e.g. face='sans-serif' &/or size='12', because the stylesheet can now do that for you. On the other hand, it's possible that the patterns 'face='sans-serif' or 'size='12' could show up in normal text (though admittedly that's unlikely). In fact, what you really want to know is wherever those patterns show up in a font tag, but you don't care about anywhere else that they might appear. Here's one way to find that pattern:
This does a number of things. The -i tells grep to ignore case (otherwise it's case sensitive, and won't match 'FONT' if you're looking for 'font' or 'Font'). The -r tells it to recursively descend through the directories from wherever the command starts -- in this case, all htm and html files in the current directory. Everything in single quotes is the pattern we're matching. We tell grep to match on any text that starts with ' (thus staying within the font tag), and then either the face or size definition that we're interested in. The one glitch here is that line breaks can break things, though there are various ways around that. Finding them is left as the proverbial exercise for the reader. :)
The next question is, what do you want to do with this information you've come up with? Presumably you want to edit those files in order to fix them, right? With that in mind, maybe it would be useful to just make a list of matches. Grep normally outputs all the lines that match the pattern, but if you just want the filenames, use the -l switch. If you want to save the results into a file, redirect the output of the command accordingly. With those changes, we now have:
Great. But we can do better still. If you are comforable with the vi editor, you can call vi with that command directly. The trick is to wrap the command in backticks (`). This is a cool little Unix trick that runs the contained command & returns the result for whatever you want to do with it. Thus you can simply put this command:
The result of this command, as far as your tcsh shell is concerned, is something along the lines of
etc. The beautiful thing here is that if you quit vi & re-run the command later, it will be able to effectively 'pick up where you left off', since files you've already edited will presumably no longer match the grep command.
And if you want to get really ambitious, you can use these techniques in ways that allow you to do all your editing directly from the command line, without having to go into an interactive editor such as vi or emacs or whatever. If you make it this far in your experiments, then the next step is to learn to filter the results of a match and process the filtered data in some way, using tools such as sed, awk, and perl. Using these tools, you can find all instances of the pattern in question, break it down however you like, substitute or shuffle the parts around however you like, and then build it all back up again. This is fun stuff! By this point, you're getting pretty heavily into Unix arcana, and the best book that I've seen about these tricks is O'Reilly's Unix Power Tools, by various authors. If you really want to leverage the power of the tools that all Unixes come with, including OSX, then this is a great place to both start & end up. There's plenty of material in there to keep you busy for months & years...
Check compatibility
You can upgrade to OS Yosemite on any of the following Mac models. Your Mac also needs at least 2GB of memory and 8GB of available storage space.
MacBook introduced in 2009 or later, plus MacBook (13-inch, Aluminum, Late 2008) MacBook Air introduced in late 2008 or later MacBook Pro introduced in mid 2007 or later Mac mini introduced in early 2009 or later iMac introduced in mid 2007 or later Mac Pro introduced in early 2008 or later Xserve models introduced in early 2009
To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu . If your Mac isn't compatible with OS X Yosemite, the installer will let you know.
Make a backup
Before installing any upgrade, it’s a good idea to back up your Mac. Time Machine makes it simple, and other backup methods are also available. Learn how to back up your Mac.
Get connected
It takes time to download and install OS X, so make sure that you have a reliable Internet connection. If you're using a Mac notebook computer, plug it into AC power.
Download OS X Yosemite
For the strongest security and latest features, find out whether you can upgrade to macOS Catalina, the latest version of macOS.
If you still need OS X Yosemite, use this link: Download OS X Yosemite. A file named InstallMacOSX.dmg will download to your Mac.
Install the macOS installer
Double-click the downloaded file to open a window showing its contents. Then double-click the file within, named InstallMacOSX.pkg.
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Follow the onscreen instructions, which will guide you through the steps necessary to install.
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Begin installation
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After installation of the installer is complete, open the Applications folder on your Mac, then double-click the file named Install OS X Yosemite.
Click Continue and follow the onscreen instructions. You might find it easiest to begin installation in the evening so that it can complete overnight, if needed.
Allow installation to complete
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Please allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both OS X and related updates to your Mac firmware.
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OS X Yosemite won't install on top of a later version of macOS, but you can erase your disk first or install on another disk.