AWK ONE-LINERS EXPLAINED EBOOK

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/r/programming is a reddit for discussion and news about computer programming. Guidelines. Please keep submissions on topic and of high. I wrote an ebook 2 months ago on Awk called "Awk One-Liners Explained." http:// tronunbucambrin.tk It teaches Awk through. Here is the Awk One-Liners Explained article: Part One, Part Two, Part My future plans are to publish a free ebook with all the one-liners.


Awk One-liners Explained Ebook

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This is a preview copy of my first ever e-book. The e-book is called "Awk One- Liners Explained" and it explains 70 short awk programs for doing various text. This is my second e-book called "Sed One-Liners Explained". The ebook explains 27 Join pairs of lines side-by-side (emulates "paste" Unix command). Print UNIX time (seconds since Jan 1, , UTC). Print . Thanks! Thank you for downloading my "Perl One-Liners Explained" e-book! This is.

If you want to substitute just one, use the sub function! Substitute "foo" with "bar" only on lines that do not contain "baz". It works exactly the same way as the previous one, except it operates on lines that do not contain match this pattern. Change "scarlet" or "ruby" or "puce" to "red".

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This one-liner makes use of extended regular expression alternation operator pipe. If the line matches, gsub replaces all the matches with "red". This is the trickiest one-liner today. It starts by recording all the lines in the array "a". For example, if the input to this program was three lines "foo", "bar", and "baz", then the array "a" would contain the following values: The END block loops over the elements in the array "a" and prints the recorded lines.

In our example with "foo", "bar", "baz" the END block does the following:.

Article series: CommandLineFu, BASH, AWK, Perl, SED One-Liners Explained

First it prints out j[2], then j[1] and then j[0]. The output is three separate lines "baz", "bar" and "foo". As you can see the input was reversed. Then the "getline t" function is executed. Awk then continues with the next line.

If the line does not end with a backslash, Awk just prints it out with "1". Unfortunately this one liner fails to join more than 2 lines this is left as an exercise to the reader to come up with a one-liner that joins arbitrary number of lines that end with backslash: This is the first time we see the -F argument passed to Awk.

For example, if the line is "foo-bar-baz" and -F is "-", then the line will be split into three fields: The entries in the file are separated by a colon ": If we split this line on ": The one-liner does just that - it splits the line on ": After Awk has finished processing the input, sort program sorts the usernames and outputs them.

This one liner is obvious. For example, if the input line is "foo bar", then after running this program the output will be "bar foo". This one-liner uses a temporary variable called "temp". This procedure swaps the first two fields on every line. For example, if the input is "foo bar baz", then the output will be "bar foo baz". We saw the "NF" variable that stands for Number of Fields in the part one of this article. After processing each line, Awk sets the NF variable to number of fields found on that line.

This one-liner loops in reverse order starting from NF to 1 and outputs the fields one by one. After that it prints a newline character. Variables in Awk don't need to be initialized or declared before they are being used. They come into existence the first time they are used. Upon reading the next line, it compares if the previous line in variable "a" is not the same as the current one "a!

Then the program saves the current line in variable "a" again and the same process continues over and over again. This one-liner is actually incorrect. It uses a regular expression matching operator "! If the previous line was something like "fooz" and the new one is "foo", then it won't get output, even though they are not duplicate lines. This one-liner is very idiomatic.

It registers the lines seen in the associative-array "a" arrays are always associative in Awk and at the same time tests if it had seen the line before.

When Awk sees the first "foo", it evaluates the expression "! Next Awk sees "bar", it does exactly the same what it did to "foo" and prints out "bar".

Now Awk sees the second "foo". This time "a["foo"]" is true, "! Finally Awk sees "baz" and prints it out because "! Here is another one-liner to do the same. Eric in his one-liners says it's the most efficient way to do it.

It's basically the same as previous one, except that it uses the 'in' operator. Given an array "a", an expression "foo in a" tests if variable "foo" is in "a". We saw the ORS variable in part one of the article.

This variable gets appended after every line that gets output. In this one-liner it gets changed on every 5th line from a comma to a newline. For lines 1, 2, 3, 4 it's a comma, for line 5 it's a newline, for lines 6, 7, 8, 9 it's a comma, for line 10 a newline, etc.

Awesome news! I just wrote my first e-book called Awk One-Liners Explained.

I improved the explanations of the one-liners in this article series, added new one-liners and added three new chapters:. I hope you learned something new. If you liked this article, you'll also like a very similar article about sed — the superman of Unix stream editing. Read this article here Sed One-Liners Explained.

Have fun with these one-liners and see you next time! Text Conversion and Substitution Last updated 3 weeks ago. Eric Pement's Awk one-liners collection consists of five sections: If you specify -n to sed, like this:. Then sed will no longer print the pattern space when it reaches the end of the script.

So if you run this program on our sample le above, there will be no output. You must use seds p command to force sed to print the line: As you can see, sed commands are separated by the ; character.

You can also use -e switch to separate the commands: Its the same as if you used ;. Next, lets take a look at the -i command line argument. This one forces sed to do in-place editing of the le, meaning it reads the contents of the le, executes the commands, and places the new contents back in the le.

Here is an example. Suppose you have a le called "users", with the following content: And you wish to replace the ": Then you can do it as easily as: Be very careful when using -i as its destructive and its not reversible! Its always safer to run sed without -i, and then replace the le yourself. Actually, before we look at the hold buer, lets take a look at addresses and ranges. Addresses allow you to restrict sed commands to certain lines, or ranges of lines. The simplest address is a single number that limits sed commands to the given line number: So if there is a "foo" on the 5th line, it will be replaced with "bar".

No other lines will be touched. The addresses can be also inverted with the! To match all lines that are not the 5th line lines , plus lines The inversion can be applied to any address.

Next, you can also limit sed commands to a range of lines by specifying two numbers, separated by a comma: Here is a quick, useful one-liner. Suppose you want to print lines 5 10 in the le. You can rst disable implicit line printing with the -n command line switch, and then use the p command on lines 5 This will execute the p command only on lines 5 No other lines will be output. Pretty neat, isnt it? Here is an example that prints the last line of the le: If you specify a regex before a command, then the command will only get executed on lines that match the regex.

Check this out:. For example, it prints lines like "ab", "aab", "aaabbbbb", "fooab", etc. There is also an expression to match a range between two regexes. It applies the d command that stands for delete. Now lets take a look at the hold buer. Suppose you have a problem where you want to print the line before the line that matches a regular expression.

How do you do this? If sed didnt have a hold buer, things would be tough, but with hold buer we can always save the current line to the hold buer, and then let sed read in the next line. Now if the next line matches the regex, we would just print the hold buer, which holds the previous line. Easy, right? The command for copying the current pattern space to the hold buer is h. The command for copying the hold buer back to the pattern space is g.

The command for exchanging the hold buer and the pattern space is x.

We just have to choose the right commands to solve this problem. Here is the solution: It works this way every line gets copied to the hold buer with the h command at the end of the script.

Also notice the command grouping. Several commands can be grouped and executed only for a specic address or range.

To x this, we can limit the p command to all lines that are not the rst line with the 1! Notice the 1! This says call the p command on all the lines that are not the 1st line.

I think that this is a great introduction to sed one-liners that covers the most important concepts in sed. Overall this book contains exactly well-explained one-liners. Once you work through them, youll have rewired your brain to "think in sed".

In other words, youll have learned how to manipulate the pattern space, the hold buer and youll know when to print the data to get the results that you need. Enjoy this book!

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This sed one-liner uses the G command. In this one-liner the hold buer is empty all the time only three commands - h, H and x modify the hold buer , so we end up simply appending a newline to the pattern space for every line.

Once all the commands have been processed in this case just the G command , sed sends the contents of pattern space to the output stream followed by a newline. So there we have it, each line now ends with two newlines one added by the G command and the other implicitly by seds printing mechanism. File has been double spaced. Sed allows the commands to be restricted only to certain lines.

Awk and Sed One-Liners Explained

But which are those? Remember that before doing the regular expression match sed pushes the input line to pattern space. When doing it, sed strips the trailing 7.

This is my second e-book called "Sed One-Liners Explained". The ebook explains sed programs for various text processing tasks such as line spacing, line numbering, text conversion and substitution, selective printing and deleting of certain lines and many others.

Get your copy of the book at: Flag for inappropriate content. Related titles. Billing system for information dispersal system US patent Virtualized data storage vaults on a dispersed data storage network US patent Jump to Page.

Search inside document. Preview copy first 16 pages Get full e-book at www. C Debugging sed Scripts with sed-sed Index vi 80 80 81 88 Preview copy first 16 pages Get full e-book at www. That vii Preview copy first 16 pages Get full e-book at www. If you specify -n to sed, like this: Check this out: When doing it, sed strips the trailing 7 Preview copy first 16 pages Get full e-book at www. Get the full e-book at: Mohit Modi. Hardeep Singh. Peteris Krumins.

El Presidente. Sandeep Kumar G Abbagouni. Deddy Rimawan. The Recipe Club.Click on http: If you specify -n to sed, like this: If you enjoyed it and would like to receive my posts automatically, you can subscribe to new posts via rss feed or email.

Delete trailing whitespace spaces and tabs from the end of each line rtrim. It contains the number of fields the current line was split into. Peteris Krumins. There is no way you can make it faster in python.

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