Unbuffer

Unbuffer is a command for Unix-like systems that runs another command in a pseudoterminal (PTY) such as to have the effect that the command's standard output is directly connected to a terminal or terminal emulator. This can be useful to disable buffering, as per its namesake; it is also useful for commands that detect the output device and behave differently, to force the normal behaviour, such as to keep ANSI colour enabled even if output is being piped into another process/command. The unbuffer command is written in Tool Command Language (Tcl) and is bundled with the Expect project.

Examples

NVLC's lengthy help output produces colour-coded presentation of headings, options, and arguments to ease navigation and reading – but only if it detects that its stdout is connected to a terminal device, or something that behaves as such. Contrarily, it is common practice to pipe such lengthy output into a pager, such as less, for example, to avoid flooding one's terminal. If NVLC detects that its output is a pipe then it disables its colour formatting, even though less can display colour using the -R option. To manage the lengthy output both with colour and with paging, the unbuffer command can be employed, as follows:-

unbuffer nvlc --help | less -M -R

The ls command (from GNU Coreutils, at least) supports the option --colour=always, eliminating the need for unbuffer in this instance. However, there are other behaviours of ls for which unbuffer may still be useful, such as for its tabulation. Normally the output of ls is tabulated, making better use of the full width of the terminal; but when piped, ls disables its tabulation:-

$ ls --color=always /proc/ | head --lines=2
1
10

To restore the tabulation, unbuffer can be applied in the same way as before:-

$ unbuffer ls --color=always /proc/ | head --lines=2
1      13971  18     2124   25516  31093  369   7104  90             kpagecount
10     14     1812   2126   25561  31972  3696  729   9025           kpageflags

References

This article "Unbuffer" is from Wikipedia. The list of its authors can be seen in its historical and/or the page Edithistory:Unbuffer. Articles copied from Draft Namespace on Wikipedia could be seen on the Draft Namespace of Wikipedia and not main one.

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