Introduction to JQ
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The document is an introduction to jq, a lightweight command-line JSON processor, covering its functionality, basic filters, operators, and functions. Key features of jq include the ability to manipulate JSON data with filters similar to text processing commands in Unix. The document also touches on regular expressions and streaming input capabilities within jq, making it a versatile tool for handling JSON data.
![Basic Filters
1. Identity (.): The simplest filter. Takes an input and gives an unchanged output. Can
be useful for pretty-printing JSON output from, say, curl.
2. Object Identifier-Index (.foo): We can call it the simplest useful function. It
produces value at index foo or null if there is none.
3. Array Index.[2]: Filter gives output using the given array index. Arrays are zero
based, so .[2] will return the third element. Negative indexing is also possible.
Array/string slice filter is also similar to this.
4. Comma(,): If two filters are separated by comma, the same input will be fed to
both the filters and their outputs will be concatenated in the order the filters were
mentioned.
5. Pipe (|): The | operator combines two filters by feeding the output(s) of the one on
the left into the input of the one on the right. It’s pretty much the same as the Unix
shell’s pipe.](https://image.slidesharecdn.com/jqsession-200601082926/85/Introduction-to-JQ-5-320.jpg)
![Functions
Functions in jq can be defined using the ‘def’ keyword and then used as we use filters
in jq.
Example: def increment: .+1; map(increment)
Input: [1,2,3,4]
Output: [2,3,4,5]](https://image.slidesharecdn.com/jqsession-200601082926/85/Introduction-to-JQ-8-320.jpg)
![Regular Expressions
The Oniguruma regular expression library is used in Jq.
The Jq regular expression can be used with the following syntax:
● STRING | FILTER( REGEX )
● STRING | FILTER( REGEX; FLAGS )
● STRING | FILTER( [REGEX] )
● STRING | FILTER( [REGEX, FLAGS] )
Here, STRING, REGEX, and FLAGS are jq strings and subject to interpolation.
FILTER is one of the test, match and capture filters.](https://image.slidesharecdn.com/jqsession-200601082926/85/Introduction-to-JQ-9-320.jpg)
Introduction to JQ
- 1. Introduction to jq Presented By: Etash Singh Software Consultant Knoldus Inc.
- 2. About Knoldus Knoldus is a technology consulting firm with focus on modernizing the digital systems at the pace your business demands. DevOps Functional. Reactive. Cloud Native
- 3. 01 What is jq? 02 Basic Filters 03 Operators and Functions 04 Conditional and Comparisons 05 Functions Our Agenda 06 Regular Expressions and Streams
- 4. c What is jq? jq is a lightweight and flexible command-line JSON processor. 1. jq is like sed for JSON. We can use it to play with JSON with the same ease that sed, awk, grep let us play with text. 2. jq is written in portable C and has zero runtime dependencies.
- 5. Basic Filters 1. Identity (.): The simplest filter. Takes an input and gives an unchanged output. Can be useful for pretty-printing JSON output from, say, curl. 2. Object Identifier-Index (.foo): We can call it the simplest useful function. It produces value at index foo or null if there is none. 3. Array Index.[2]: Filter gives output using the given array index. Arrays are zero based, so .[2] will return the third element. Negative indexing is also possible. Array/string slice filter is also similar to this. 4. Comma(,): If two filters are separated by comma, the same input will be fed to both the filters and their outputs will be concatenated in the order the filters were mentioned. 5. Pipe (|): The | operator combines two filters by feeding the output(s) of the one on the left into the input of the one on the right. It’s pretty much the same as the Unix shell’s pipe.
- 6. Built In Operators and and functions 1. Addition (+): The operator + takes two filters, applies them both to the same input, and adds the results together. 2. Subtraction (-): As well as normal arithmetic subtraction on numbers, the - operator can be used on arrays to remove all occurrences of the second array’s elements from the first array. 3. length: It returns the length of a string, array, object or null. 4. keys: When provided with an object, the key function returns the keys in it. 5. has(key): Returns true if an object has the specified key, otherwise returns false. 6. map(x): For any filter x, map(x) will run that filter for each element of the input array, and return the outputs in a new array. 7. del(): Removes key and its corresponding value from an object 8. select(): The select function produces an output if the condition provided is true otherwise no output at all. 9. sort: This function sorts the input which must be an array.
- 7. Conditionals and Comparisons 1. ==, != 2. if-else-then 3. >,<,>=,<= 4. Alternative Operator(//): A filter of form a//b produces ‘a’ if ‘a’ returns anything other than false or null. Otherwise it returns ‘b’
- 8. Functions Functions in jq can be defined using the ‘def’ keyword and then used as we use filters in jq. Example: def increment: .+1; map(increment) Input: [1,2,3,4] Output: [2,3,4,5]
- 9. Regular Expressions The Oniguruma regular expression library is used in Jq. The Jq regular expression can be used with the following syntax: ● STRING | FILTER( REGEX ) ● STRING | FILTER( REGEX; FLAGS ) ● STRING | FILTER( [REGEX] ) ● STRING | FILTER( [REGEX, FLAGS] ) Here, STRING, REGEX, and FLAGS are jq strings and subject to interpolation. FILTER is one of the test, match and capture filters.
- 10. Regular Expressions Flags is one of the following which are defined below: ● g - Global search for finding all matches and not just one ● i - Case insensitive search ● m - Multi-line mode ● n - Ignore empty matches ● p - Both s and m modes are enabled ● s - Single line mode ● l - Find longest possible match ● x - Extended regex format (ignore whitespace and formats.
- 11. Streaming The --stream flag is used to parse the input text as a stream, allowing jq programs to start processing large JSON texts immediately rather than after the parse completes. There are 3 built-in functions to handle out streaming input: 1. truncate_stream(stream_expression) 2. from_stream(stream_expression) 3. to_stream(stream_expression)
- 12. DEMO
- 13. OUR CHARTInsert Your Subtitle Here Reference https://stedolan.github.io/jq/manual/#ConditionalsandComparisons
- 14. Thank You!