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Printf (Unix)

printf
DevelopersVarious open-source and commercial developers
Operating systemUnix and Unix-like
PlatformCross-platform
TypeCommand
Licensecoreutils: GPLv3+[1]

printf is a shell command that formats and outputs text like the same-named C function. It is available in a variety of Unix and Unix-like systems. Some shells implement the command as builtin and some provide it as a utility program[2]

The command has similar syntax and semantics as the library function. The command outputs text to standard output[3] as specified by a format string and a list of values. Characters of the format string are copied to the output verbatim except when a format specifier is found which causes a value to be output per the specifier.

The command has some aspects unlike the library function. In addition to the library function format specifiers, %b causes the command to expand backslash escape sequences (for example \n for newline), and %q outputs an item that can be used as shell input.[3] The value used for an unmatched specifier (too few values) is an empty string for %s or 0 for a numeric specifier. If there are more values than specifiers, then the command restarts processing the format string from its beginning,

The command is part of the X/Open Portability Guide since issue 4 of 1992. It was inherited into the first version of POSIX.1 and the Single Unix Specification.[4] It first appeared in 4.3BSD-Reno.[5]

The implementation bundled in GNU Core Utilities was written by David MacKenzie. It has an extension %q for escaping strings in POSIX-shell format.[3]

Examples

This prints a list of numbers: 

$ for N in 4 8 10; do printf " >> %03d << \n" $N; done
 >> 004 <<
 >> 008 <<
 >> 010 <<

This produces output for a directory's content similar to ls: 

$ printf "%s\n" *


References

  1. ^ "printf(1): format/print data - Linux man page". linux.die.net. Archived from the original on 2018-11-21. Retrieved 2019-02-24.
  2. ^ "GNU Coreutils". www.gnu.org. Archived from the original on 2004-02-05. Retrieved 2019-02-27.
  3. ^ a b c printf(1) – Linux User Manual – User Commands from Manned.org
  4. ^ printf – Shell and Utilities Reference, The Single UNIX Specification, Version 5 from The Open Group
  5. ^ printf(1) – FreeBSD General Commands Manual
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