[SOLVED] What does 'printf -v' do?

Issue

After having come across several times this printf -v in bash script examples on the net, as well as several questions on stackoverflow, I could not find a proper explanation in the printf manpages.

man printf or man 3 printf do not help me.

Where do I have to look for?

Solution

There are several printf commands within Linux:

1. printf the known C function (described in man 3 printf)
2. GNU coreutils printf, located in /usr/bin/printf (see man 1 printf or info coreutils printf)
3. Bash's builtin printf (see the SHELL BUILTIN COMMANDS section from man bash or info bash printf or help printf).

To find out, what you exactly need, use type <command> to find out what is used in particular:

root@pi:~# type -a printf
printf is a shell builtin
printf is /usr/bin/printf
printf is /bin/printf

So number 3 is the solution here.

root@pi:~# help printf
printf: printf [-v var] format [arguments]
    Formats and prints ARGUMENTS under control of the FORMAT.
    
    Options:
      -v var    assign the output to shell variable VAR rather than
            display it on the standard output
    
    FORMAT is a character string which contains three types of objects: plain
    characters, which are simply copied to standard output; character escape
    sequences, which are converted and copied to the standard output; and
    format specifications, each of which causes printing of the next successive
    argument.
    
    In addition to the standard format specifications described in printf(1),
    printf interprets:
    
      %b    expand backslash escape sequences in the corresponding argument
      %q    quote the argument in a way that can be reused as shell input
      %Q    like %q, but apply any precision to the unquoted argument before
            quoting
      %(fmt)T   output the date-time string resulting from using FMT as a format
                string for strftime(3)
    
    The format is re-used as necessary to consume all of the arguments.  If
    there are fewer arguments than the format requires,  extra format
    specifications behave as if a zero value or null string, as appropriate,
    had been supplied.
    
    Exit Status:
    Returns success unless an invalid option is given or a write or assignment
    error occurs.

Answered By - sjas

Answer Checked By - Robin (WPSolving Admin)