Tag: grep

Let’s Learn About Grep

I’ve used the grep command many times but haven’t written an article to learn about grep. It seems like a good idea to do so so I can reference this article. That’s something that’s considered a good thing.

The thing is, I’ve tried to write this article before and it just came out terrible. That article never got published. It just wasn’t good enough. As you’ve seen the quality of some of these articles, tells you how bad that attempt went. 

You won’t need to install anything for this article. If you’re using a desktop or a server, you have grep. I’d expect to find grep in embedded systems because it’s just a useful tool. I suppose some companies might have ripped it out of their devices to save space and stop you from rooting around and messing with things.

So, I decided I’d do what I’d done before. I reached out to my buddy ChatGPT and asked them to write an article. Sure enough, ChatGPT did a fine job at it. This doesn’t save me much time. I still need to do all the formatting and that takes more time than you might expect.

So then, let’s get into the article…

About Grep:

The grep command in Linux is a powerful tool used for searching and manipulating text within files or standard input streams. It stands for “global regular expression print” and is primarily used to match patterns in text and display the lines that contain those patterns. grep is highly versatile and widely used in various scenarios, ranging from simple text searches to complex pattern matching and filtering tasks.

Basic Syntax:

The basic syntax for grep is as follows:

  • pattern: The pattern to search for. It can be a simple string or a complex regular expression.
  • file: Optional. The file(s) to search. If not specified, grep reads from standard input.
Common Options:
  • -i or --ignore-case: Ignore case distinctions.
  • -v or --invert-match: Invert the sense of matching, displaying non-matching lines.
  • -r or --recursive: Recursively search subdirectories.
  • -n or --line-number: Prefix each line of output with its line number.
  • -l or --files-with-matches: Display only the names of files containing matches.
  • -E or --extended-regexp: Interpret pattern as an extended regular expression (ERE).
  • -F or --fixed-strings: Interpret pattern as a list of fixed strings (not regular expressions).
Examples:

Basic Text Search:

This command searches for the occurrence of “keyword” in the file file.txt and displays all lines containing that keyword.

Case Insensitive Search:

This command performs a case-insensitive search for the pattern “pattern” in the file file.txt.

Invert Match:

This command displays all lines in file.txt that do not contain the word “exclude”.

Search in Multiple Files:

This command searches for the pattern in both file1.txt and file2.txt.

Recursive Search:

This command recursively searches for the pattern in all files within the specified directory and its subdirectories.

Display Line Numbers:

This command displays the line numbers along with the lines containing the pattern in file.txt.

Regular Expressions:

grep supports regular expressions, allowing for more advanced pattern matching. Regular expressions enable users to define complex search patterns, such as matching specific character sequences, ranges, or repetitions.

For example:

  • . matches any single character.
  • ^ matches the beginning of a line.
  • $ matches the end of a line.
  • [ ] specifies a character class.
  • * matches zero or more occurrences of the preceding element.
  • \ is used to escape special characters.
Additional Information:

The grep command is an essential tool for text processing and manipulation in the Linux terminal. Its versatility, combined with regular expressions, allows users to perform a wide range of tasks, including simple text searches, pattern matching, filtering, and data extraction. Whether it’s analyzing log files, searching for specific information in codebases, or performing system administration tasks, grep remains an indispensable utility for Linux users. Understanding its capabilities and various options can greatly enhance productivity and efficiency when working with text data in the terminal.

Closure:

So, there you have it. You have an AI-generated article about grep. It’s formatted quite differently than I’d normally format it, but it works. I dare say that AI did the job better than I had when I tried in the past.

People worry about AI but it’s just a tool. I am slowly learning when to make it useful to me. I’m not sure how many jobs AI is going to replace, but I can see lots of ways to use AI to make life easier. I can see ways to make AI more educational, such as in this article. It’s a nice overview, I think.

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

Find Files Created On A Specific Date

We sure do have a lot of file management articles and this is another one that will help you find files created on a specific date. This is a relatively easy task and you won’t even have to install anything new. If you want to find files created on a specific date, you might as well use this method!

Here’s a similar article.

Find Files Modified On A Specific Day

So, what is file management? To me, it’s manipulating files on your file system. It’s gathering information about the files on your file system. That’s what I mean when I say ‘file management’. I’ve covered a lot of articles with this as a subject.

Seriously… I tag articles with various terms. There are pages and pages of articles that have been tagged with file management.

Articles Tagged With File Management

Yup, that’s a lot of articles. Managing your files is something you do on a daily basis. You’re creating, editing, and moving your files around your file system. That’s file management and that’s okay!

Because this is something you do on a daily basis, even if you don’t pay attention to it, it’s something covered often. Even if you’re just browsing the internet, you’re adding files such as cached files. If you’re emailing with an email client, you have added and deleted files – if not more. File management is a pretty big thing.

Today, we’ll be using two basic commands – ls and grep. Let’s learn more!

The ls Command:

The ls command is an application that lets you list files. There are flags you can use, but it’s a basic application that, at its core, just lists files. You don’t need to install anything. You can verify that ls is available with this command:

The output should look like this:

Check the ls man page with this command:

If you do that, you’ll see that we’re on the right path if we want to find files created on a specific date. The ls command is briefly described as this:

ls – list directory contents

We’ll be using the ls command to output a list of files and we’ll then use the pipe operator to process that output with grep.

The grep Command:

The grep command is one of those commands that’s used in conjunction with another command. By itself, it’s not that useful. It is when you use grep with other commands that you realize how powerful it is.

The grep command is usually used with the | “pipe” operator. The pipe operator takes the output from one command and processes it with another application. I’ve not yet covered this in an article, nor have  I done an article about the grep command. I should do both.

Again, you won’t need to install anything. You can verify this with this command:

The output should match this:

Next, you can check the man page with this command:

grep, egrep, fgrep, rgrep – print lines that match patterns

You can see that there are options. We’ll be using just plain grep. And, as you can deduce, this is yet another process that will help us find files created on a specific date. We’ll take the output from one command and use it with the grep command. This should appear obvious shortly if you have not yet realized how we’ll be proceeding in this article.

Find Files Created On A Specific Date:

Both ls and grep are tools used in the terminal. As such, you can be sure that you’ll need an open terminal. Either open a terminal from your application menu or open a terminal by pressing CTRL + ALT + T on your keyboard. This article assumes that you don’t have year numbers in your file names, as you’ll see…

With your terminal open, we can begin to find files created on a specific date. Further, let’s stay right there in the ~/home/user directory. We’ll keep it simple.

Let’s start with this command:

That will list all your files. Now, let’s add hidden files – with the -a (all) flag with the following command:

Next up, let’s get more information from the ls command with the -l (long listing format) flag. That looks like this:

You should now see that there’s a time listed. We’re going through this just so that the example commands work. This isn’t strictly necessary, it’s just how it is being explained in this article.

If you want, you can sort that output by time. The following example command will show you the time the files were created, starting with the most recent example.

Again, that’s not strictly necessary.

Pay attention to the date section, because that’s what we’ll be using. 

More specifically, we’ll be piping the output from the ls command to the grep command. That’s done like this:

NOTE: You’ll be grepping a pattern. So, if you look carefully, the dates from 1 to 9 have two spaces! You’ll need to grep accordingly!

So, if you wanted to list articles created on the day this will be published, the command would look like this:

Notice that there are two spaces.

If you wanted to find files created on the 10th of February, your command would be different. You don’t add a 2nd space, as there is no second space in the pattern you’re looking for:

That will show you all the files (including the hidden files) that were created on the 10th of February. It does not care about the year and doesn’t show the year field. You’re simply finding files created on a specific date (ignoring the year, of course).

This is still useful.

This is also only true for files created within the past year. The ls command will happily show the date on files older than a year.

Here’s an example where the files are older than a year:

So, to find files including the year, your command now has more spaces to contend with. For this command, you would now add two spaces between the day and the year. Like so:

See the two spaces? That’s essential.

Again, don’t forget that you need two spaces when you’re working with days that are a single digit. If I wanted to find files from the 4th of November in 2022, that command would be this:

REMEMBER: The grep command is used to find patterns and will only find the specified patterns. It’s very specific! It is also very powerful when used properly.

You can do even more with this. If you want to find files older than a year and by the specific year of their creation, you could simply run a command that looks like this:

Of course, you can substitute ‘2020’ with any year you’d like and get results – so long as you have files that were created in that year.

Also, of course, that command is ONLY useful if you do not have year numbers or numbers similar to years in file names. After all, 2022 is 2022 and grep is going to find them all. That’s what grep does – it finds patterns. As such, it’s up to you to pick the patterns you’ve used and this does have a limited functionality if you’ve gone ahead and added dates to your file names.

If you do have numbers in your file names and you don’t have spaces, you can still grep for a pattern. For example, this might work assuming no space in your file name is in front of the year field – which there generally shouldn’t be:

I can’t be too specific because I don’t know if you’ve put numbers/years in your file names. If you have, grep will equally find those. This whole article assumes that you’ve done nothing of the sort.

This can be even handier and here’s a little bit of some bonus information.

Let’s say you have a directory where you’ve stored files for years. Further, you want to know how many files you created in the year 2022. This directory contains files containing many years and you don’t want to just count them.

Well, you can do something about that!

That command lists the files. The grep command then finds files created in 2022. You then pipe that output to the ‘wc’ command to count the lines.

Here’s an example output:

That means I added 8 files to that directory in the year 2023.

It’s pretty complicated. If you have years and spaces in your file names, this isn’t going to work that well for you. If you use patterns that match the output from the ls command, grep will find them. That’s what grep does.

While this does have a bit of a limited use case, it’s more of an exploration of what you can do with two simple commands. Unless you use matching patterns in your file names, this should work just famously for you. Otherwise, not so much – but you can have both fun trying AND you can look for other patterns that you can pass to grep.

Closure:

Well, that was kind of fun. We used the ls and grep commands to find files created on a specific date. There are always so many fun things to do with Linux. Many of these fun things can be done in the terminal. I like to think we both learn and have fun here on this site.

This can also be a handy tool. Let’s say you made some changes and then had some trouble later. You know you added files, but you can’t remember which files those were. Before restoring from a backup, you decide you want to troubleshoot. To do so, you start by finding files you created on the same day that you last changed your system.

Of course, this can be useful in a business setting. If you need to account for a problem, you can find the files created that day. Should there be something amiss, you can find files created on a specific date. If, for example, files were created on a date when no files should have been created… Well, you get the idea.

Perhaps more importantly, this shows what you can do with just two basic Linux commands. You’ll find ls and grep on every single desktop Linux (or server Linux) you touch. There’s no need for you to install something. You don’t have to worry about which package manager you use or building software from scratch because the developers didn’t release a package for your distro. You just use the commands that are already available.

Anyhow, this article is already too long. Sorry about that…

I kid. If I was sorry, I wouldn’t have done it in the first place! Ha! Take that!

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Yet Another Way To Find Files By Extension

You might look at the title and think that you’ve seen this before, and you have, but this is another way to find files by extension. That’s right! This is Linux! There’s almost always a variety of ways to think about this. There are almost always a variety of ways to accomplish the same task!

Well, this article will touch on a theme we’ve seen before. We’ve seen it recently. I’ve even explained why you might want to find files by their extension type. Fortunately, I’ve even explained the limitations this has.

See a shell script file could have a .txt extension but still work just fine as a script. Linux cares about the file itself more than it cares about the extension. If you have files mislabeled as an .iso file, this operation will still list them as .iso files. This is only about the extension and using that as a search category. It has limitations.

You can read these articles for more:

Another Way To Locate Files By Extension
Find Multiple Filenames By Extension – With Locate
How To: Find Multiple Filenames By Extension

See? It might seem that this article is like beating a dead horse, but it’s not. There are use cases for all of these options, including the option I’ll give you in this article.

Also, it seems like a good day to take it easy. Life has sent me a bit of extra stress. That won’t stop me from writing this article. It seems nothing will stop me from writing these articles!

The ‘ls’ Command:

This is kind of the sledgehammer way to find files by their extension. It’s a good way. It’s even an easy way to remember, without needing extra commands. At the same time, it’s a pretty basic way to do so.

The first command we’ll work with is one you have installed already. You won’t need to add any software to follow along with this article. We’re simply going to use the ls command to list directory contents. 

If you check the man page for the ls command, you’ll see this:

ls – list directory contents

What did I say in the paragraph before that? I said we’re going to list directory contents. Sure enough, Linux provides the perfect tool for this. 

As an aside, what you can accomplish with a basic Linux install is amazing. You can accomplish a whole lot of work without actually adding any additional software. This is awesome. Thank you, Linux.

The ‘grep’ Command:

The second command we’ll be using is the grep command. If you’re a regular on this site, you’ll have used the grep command many times. You can think of the grep command as a filter. You use the grep command to process the output of another command (more often than not) and, more specifically, you use it to filter that output.

You want to use grep when you’re trying to isolate some information. Well, sure enough, we can check the man page for grep. If you do so, you’ll find that grep accurately describes itself like this:

grep, egrep, fgrep, rgrep – print lines that match patterns

You’ll see that grep comes in many forms. You’ll also see that it’s used to print lines that match patterns. The command is filtering out those lines that don’t match the prescribed pattern.

In fact, I used it as an example in the previous article:

Find Out When A File Was Created

Scroll down to see how you can use the grep command to filter out the lines that aren’t important when you simply want to find out when a file was created. Simple, eh? Yes… Simple!

Find Files By Extension:

As you can guess, we’ll be using both the ‘ls’ command and the ‘grep’ command to find files by extension. As those are terminal-based commands, this will be a terminal-based article. You’ll need to open a terminal and you can (more often than not) do so by pressing CTRL + ALT + T.

With your terminal now open, this is the syntax I want you to use for this exercise. We’ll keep it simple:

If you’ve used mix-case, maybe having extensions of .TXT (in capital letters), you can add the -i flag to the grep command. That will (don’t forget to check the man page) tell the grep command to ignore the case. So, an example of the syntax for that command might be:

For example, I might want to search my ~/Downloads directory for .iso files, finding the various distros I’ve downloaded on this computer. If I wanted to do that, my command would look like this:

And, sure enough, here’s an example output from that very command:

See? That output shows you all the .iso files that I have in my ~/Downloads directory. There’s no fuss. There’s no muss. It’s just a simple way to find files by extension.

Anyone can do it and they won’t need any additional software to do so. Everyone (except maybe someone with a very light embedded Linux system – and probably still them) can find files by extension without adding anything to their system. It’s maybe a bit creative, but it’s effective. I’m not sure about you, but I like effective things. This meets that definition squarely – it’s effective.

Closure:

Well, I guess this is still a fairly long article. I’ve been making them longer and this one just got written that way. My style of longer writing isn’t without thought. I have altered the format of these articles a half-dozen times.

Each time I do so, I do so for you. The goal of altering the format is to make it easier for you to digest and to offer more information than previous articles – even for the more basic articles like this one. I do not know if I’ll settle on this style. Evidence would suggest that I’ll improve upon it as I go.

I welcome feedback on this. I don’t suppose you’ll give me that feedback. The odds are good that you won’t even read this far down. Still, please let me know if you like the current writing style. I’ve consistently written to a formula, but that formula has changed over time. This is the most recent iteration, so please let me know what you think. Thanks!

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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