printf format specifier %h; is it standard?

Commands

printf 'ABC$def%hx\n' 10  # output: ABC$defa
printf 'ABC$def%s\n' 10   # output: ABC$def10

work as expected.... but I cannot find any info about %h.
Is it available on all systems?

Is it available on all systems?

You are using printf command in shell. This command might have the h format length modifier , when:

• you are using Bash, it will be builtin printf command built in in Bash inside it.

  • "h" is there at least 16 years ago, Bash 2.02

  • https://github.com/bminor/bash/blame/master/builtins/printf.def#L187

• you are using busybox ash, then:

  • 'h' was added 17 years ago from the project beginning

  • https://github.com/mirror/busybox/blame/master/coreutils/printf.c#L351

• you are using GNU coreutils, then:

  • 'h' was added 33 years ago

  • https://github.com/coreutils/coreutils/blame/c41ca2814d2ffad5fff9b9526d1be9eb5366d72d/src/printf.c#L635

The info about h comes from C standard:

• h was there in printf C in 1989 https://port70.net/~nsz/c/c89/c89-draft.html#4.9.6.1
• for explanation what h does in C programming language, check https://en.cppreference.com/w/c/io/fprintf

However, h might not be supported, when:

• using Kernel dash shell printf builtin

  • Ubuntu uses dash by default

  • https://web.git.kernel.org/pub/scm/utils/dash/dash.git/tree/src/bltin/printf.c#n263

  • # printf "%hhx" 10
    dash: 2: printf: %h: invalid directive
    

• using FreeBSD

  • I do not see length modifier mentioned, except for L for floats

    • https://man.freebsd.org/cgi/man.cgi?query=printf&manpath=FreeBSD+12-current

  • and I do not see it in source code https://github.com/lattera/freebsd/blob/master/usr.bin/printf/printf.c#L328

  • and I tested (side note: vagrant booted with Bash on freebsd anyway)

    • vagrant@freebsd13:~ $ printf 'ABC$def%hx\n' 10
      printf: illegal format character h
      

• on macOS /usr/bin/printf does not support it, which most probably is the same version from BSD

• and reading POSIX I do not see length modifier mentioned:

  • https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap05.html#tag_05

I say, if working with Bash, it will be available.

But it might be not available on Ubuntu and BSD. I think MacOS has Bash3 anyway.

Fun fact: what is the output of the following code printf "%hjLltzhhhjjjLLLLtttzzzx\n" 10 in Bash?

printf format specifier %h; is it standard?

There is no %h sole format specifier. The letter h is used as a modifier of the format specifier following it. In C programming language, %hhx %hx %x %llx %lx %zx %jx all take different arguments type. See table in https://en.cppreference.com/w/c/io/fprintf for explanation. In shell however it does not matter at all, and all implementation just ignore such modifiers.