>From f267fca48c2cffd0783b31c6ca82a7af56dcb327 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?P=C3=A1draig=20Brady?= Date: Sat, 21 Nov 2015 05:13:49 +0000 Subject: [PATCH] doc: provide an example for prefixing all tail output lines * doc/coreutils.texi (tail invocation): Provide an example using awk to convert tail ==> file <== headers to file: prefixes on each line. Suggested by Stephen Shirley. --- doc/coreutils.texi | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/doc/coreutils.texi b/doc/coreutils.texi index 8034807..4e8479d 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -2839,14 +2839,22 @@ tail [@var{option}]@dots{} [@var{file}]@dots{} @end example If more than one @var{file} is specified, @command{tail} prints a -one-line header consisting of: +one-line header before the output for each @var{file}, consisting of: @example ==> @var{file name} <== @end example -@noindent -before the output for each @var{file}. +For further processing of tail output, it can be useful to convert the +file headers to line prefixes, which can be done like: + +@example +tail @dots{} | +awk ' + /^==> .* <==$/ @{prefix=substr($0,5,length-8)":"; next@} + @{print prefix$0@} +' | @dots{} +@end example @cindex BSD @command{tail} GNU @command{tail} can output any amount of data (some other versions of -- 2.5.0