What is the difference between sed and awk

 

sed is a stream editor. It works with streams of characters on a per-line basis. It has a primitive programming language that includes goto-style loops and simple conditionals (in addition to pattern matching and address matching). There are essentially only two "variables": pattern space and hold space. Readability of scripts can be difficult. Mathematical operations are extraordinarily awkward at best. There are various versions of sed with different levels of support for command line options and language features.

awk is oriented toward delimited fields on a per-line basis. It has much more robust programming constructs including if/else, while, do/while and for (C-style and array iteration). There is complete support for variables and single-dimension associative arrays plus (IMO) kludgey multi-dimension arrays. Mathematical operations resemble those in C. It has printf and functions. The "K" in "AWK" stands for "Kernighan" as in "Kernighan and Ritchie" of the book "C Programming Language" fame (not to forget Aho and Weinberger). One could conceivably write a detector of academic plagiarism using awk.

GNU awk (gawk) has numerous extensions, including true multidimensional arrays in the latest version. There are other variations of awk including mawk and nawk.

Both programs use regular expressions for selecting and processing text.

I would tend to use sed where there are patterns in the text. For example, you could replace all the negative numbers in some text that are in the form "minus-sign followed by a sequence of digits" (e.g. "-231.45") with the "accountant's brackets" form (e.g. "(231.45)") using this (which has room for improvement):

sed 's/-\([0-9.]\+\)/(\1)/g' inputfile

I would use awk when the text looks more like rows and columns or, as awk refers to them "records" and "fields". If I was going to do a similar operation as above, but only on the third field in a simple comma delimited file I might do something like:

awk -F, 'BEGIN {OFS = ","} {gsub("-([0-9.]+)", "(" substr($3, 2) ")", $3); print}' inputfile

 

Of course those are just very simple examples that don't illustrate the full range of capabilities that each has to offer.

1) What is the difference between awk and sed ?

Both are tools that transform text. BUT awk can do more things besides just manipulating text. Its a programming language by itself with most of the things you learn in programming, like arrays, loops, if/else flow control etc You can "program" in sed as well, but you won't want to maintain the code written in it.

2) What kind of application are best use cases for sed and awk tools ?

Conclusion: Use sed for very simple text parsing. Anything beyond that, awk is better. In fact, you can ditch sed altogether and just use awk. Since their functions overlap and awk can do more, just use awk. You will reduce your learning curve as well.

 

Both tools are meant to work with text and there are tasks both tools can be used for.

For me the rule to separate them is: Use sed to automate tasks you would do otherwise in a text editor manually. That's why it is called stream editor. (You can use the same commands to edit text in vim). Use awk if you want to analyze text, meaning counting fields, calculate totals, extract and reorganize structures etc.

Also you should not forget about grep. Use grep if you only want to search/extract something in a text (file)

 

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