What does 'printf -v' do?

Question

After several examples of using printf -v in a bash script on the net, as well as a few questions about stackoverflow, I could not find the correct explanation in the printf man files.

man printf or man 3 printf do not help me.

Where should I look?

Answer 1

There are several printf commands in linux:

• printf as a well-known C. function (described in man 3 printf )
• GNU printf located at /usr/bin/printf . (see man printf )
• bash printf built-in . (see man bash and see the entry for it in the SHELL BUILTIN COMMANDS section). You can also find it with help printf , which will display the inline description from the man page.

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

 root@pi :~# type printf printf is a shell builtin 

So number 3 is the solution here:

printf [-v var] format [arguments]

The -v option causes the output to be assigned to the variable var rather than being printed to the standard output.

Excerpt from here:

 printf [-v var] format [arguments] Write the formatted arguments to the standard output under the control of the format. The -v option causes the output to be assigned to the variable var rather than being printed to the standard output. The 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 printf(1) format specifications, printf interprets the following extensions: %b causes printf to expand backslash escape sequences in the corresponding argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits). %q causes printf to output the corresponding argument in a format that can be reused as shell input. %(datefmt)T causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3). The corresponding argument is an integer representing the number of seconds since the epoch. Two special argument values may be used: -1 represents the current time, and -2 represents the time the shell was invoked. Arguments to non-string format specifiers are treated as C constants, except that a leading plus or minus sign is allowed, and if the leading character is a single or double quote, the value is the ASCII value of the following character. The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure.