Cannot use the pow() nor pow10() functions

[sebma]

Describe the bug
I want to divide an integer representing a throughput in bits/sec by 10^9 to get Gbits/sec but I get pow/1 is not defined errors.

To Reproduce

$ echo 7223210000 | jq -r './pow(10,9) | tostring + " bits/sec"'
jq: error: pow/1 is not defined at <top-level>, line 1:
./pow(10,9) | tostring + " bits/sec"
jq: 1 compile error
$ echo 7223210000 | jq -r './pow10(9) | tostring + " bits/sec"'
jq: error: pow10/1 is not defined at <top-level>, line 1:
./pow10(9) | tostring + " bits/sec"
jq: 1 compile error

Expected behavior

$ echo 7223210000 | jq -r './pow(10,9) | tostring + " bits/sec"'
7.22321 bits/sec
$ echo 7223210000 | jq -r './pow10(9) | tostring + " bits/sec"'
7.22321 bits/sec

Environment (please complete the following information):

• OS and Version: Linux CentOS 7.9
• jq version 1.5

Additional context
jq has been built with maths functions ( -lm) :

$ ldd $(which jq) | grep libm
        libm.so.6 => /usr/lib64/libm.so.6 (0x00007fa9155a9000)
$ rpm -qf /usr/lib64/libm.so.6
glibc-2.17-325.el7_9.x86_64

[wader]

Hey, jq uses ; as argument separator so try pow(10; 9)

[emanuele6]

pow(10,9) is the same as pow(10),pow(9) it calls pow/1 twice (and pow/1 doesn't exist).
You want to call pow/2 with two argument, so you should use pow(10;9).

bash-5.1$ jq -n 'pow(10; 9)'
1000000000

---

pow10/1 does not exist. pow10 exists as pow10/0: it takes no arguments and takes a number as input, and outputs the result; you would use it as 9 | pow10.
But keep in mind that pow10/0 doesn't work since it is non-standard and it was removed from the GNU C standard library in version 2.27, so it is not available on most systems:

bash-5.1$ jq -n '9 | pow10'
jq: error (at <unknown>): Error: pow10/0 not found at build time

[emanuele6]

Also i think it would make more sense to just use a number literal.
If you don't want to have to write 1000000000, you can just use 1e9.

jq -r '"\(. / 1e9) bits/sec"'

[sebma]

Thank you everyone for such fast reaction.

For the pow(), my bad I had forgotten that jq separated function arguments with ;

@emanuele6 For pow10, you said :

But keep in mind that pow10/0 doesn't work since it is non-standard and it was removed from the GNU C standard library in version 2.27, so it is not available on most systems:

bash-5.1$ jq -n '9 | pow10'
jq: error (at <unknown>): Error: pow10/0 not found at build time

On my system here, we're still using GNU C v2.17 (<v2.27), therefore pow10 should be here but it is not :

$ rpm -qf /usr/lib64/libm.so.6
glibc-2.17-325.el7_9.x86_64
$ jq -n '9 | pow10'
jq: error: pow10/0 is not defined at <top-level>, line 1:
9 | pow10
jq: 1 compile error

[emanuele6]

@sebma that is not really relevant.

You are using a binary package manager (not a package manager that compiles the program on your system), so you downloaded a binary executable that someone else built for you; who built the jq package may not have had such an old version of glibc.

Also you are using jq 1.5 which is ancient, so maybe pow10/0 didn't even exist yet since it prints out that error message, but I am not sure (that could be just because builtins used to be defined in a different way).

[emanuele6]

@sebma I just compiled jq 1.5 from source, and looked at its source code.
I can confirm that pow10 was not supported at all in jq 1.5, so, even if you have a binary of it that was built on a system that has pow10, you can't use it from jq.
Keep in mind that jq 1.5 was released almost 7 years ago (16 Aug 2015).

[sebma]

@emanuele6 OK, so in order to be able to use the pow10 function, one has to use jq >= 1.6 and GNU Libc < 2.27, is that correct ?

[emanuele6]

@sebma

@emanuele6 OK, so in order to be able to use the pow10 function, one has to use jq >= 1.6 and GNU Libc < 2.27, is that correct ?

In jq 1.6, you can use pow10/0 and it will exist whether it is supported or not (in jq 1.5, it does not exist at all).

If the jq binary was built on a system where the presence of pow10() was detected at compile time, and is ran on a system that has pow10(), it will return the result of calling pow10() on the input; otherwise, if it was not detected at build time, pow10 will always throw an error containing "Error: pow10/0 not found at build time" when it is run:

bash-5.1$ jq -n '9 | try pow10 catch .'
"Error: pow10/0 not found at build time"

---

Again, in your case, you don't need to use pow10/0 or pow/2 and call a C math function at all; you just want 1000000000 which, in jq, like most other programming languages (perl, python, java, javascript, awk, fortran, go, C, C++, D, ...) can be written as 1e9.

[sebma]

@emanuele6 Thanks for your explanation.