How do I use jq to convert number to string?

Question

Given the following jq command and Json:

jq '.[]|[.string,.number]|join(": ")' <<< '
[
  {
    "number": 3,
    "string": "three"
  },
  {
    "number": 7,
    "string": "seven"
  }
]
'

I'm trying to format the output as:

three: 3
seven: 7

Unfortunately, my attempt is resulting in the following error:

jq: error: string and number cannot be added

How do I convert the number to string so both can be joined?

AXE Labs · Accepted Answer · 2016-02-02 17:08:27Z

127

The jq command has the tostring function. It took me a while to learn to use it by trial and error. Here is how to use it:

jq -r '.[] | [ .string, .number|tostring ] | join(": ")' <<< '
[{ "number": 9, "string": "nine"},
 { "number": 4, "string": "four"}]
'
nine: 9
four: 4

answered Feb 2, 2016 at 17:08

AXE Labs

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3 Comments

Uncle Long Hair Over a year ago

Thank you very helpful, I find jq hard to use and poorly documented so these examples really help.

Vladyslav Didenko Over a year ago

.number|tostring worked perfectly

Tom Harrison Over a year ago

Note that if the .number|tostring is the first element of the array, it will fail. See below for note about surrounding with parens to avoid the error.

Andrew Neilson · Accepted Answer · 2017-10-10 19:51:55Z

83

An alternative and arguably more intuitive format is:

jq '.[] | .string + ": " + (.number|tostring)' <<< ...

Worth noting the need for parens around .number|tostring.

answered Oct 10, 2017 at 19:51

Andrew Neilson

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3 Comments

SebMa Over a year ago

For my use case I had to keep the parentheses to prioritize things. It's better to keep them for general use cases.

spcsLrg Over a year ago

Thank you! I found this working for me too for concat purposes, after spending hours trying in vain to make sense of jq's horribly poor documentation! (and agreed, this is more intuitive than the answer above it.)

Sridhar Sarnobat Over a year ago

I agree it's more intuitive and naturally follows when incrementally building a statement.

manatwork · Accepted Answer · 2020-12-18 00:26:31Z

19

For such simple case string interpolation's implicit casting to string will do it:

.[] | "\( .string ): \( .number )"

See it in action on jq‣play.

edited Dec 18, 2020 at 0:26

answered Aug 9, 2019 at 12:12

manatwork

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2 Comments

manatwork Over a year ago

@Ярослав Рахматуллин, that's not useless escapes. That's jq's string interpolation syntax. Ruby has "#{ 1 + 2 }", Groovy has "${ 1 + 2 }", jq has "\( 1 + 2 )".

Walter Tross Over a year ago

btw, Swift has the same string interpolation syntax

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