From: Pádraig Brady <P@draigBrady.com>
Date: Sat, 21 Nov 2015 05:13:49 +0000 (+0000)
Subject: doc: provide an example for prefixing all tail output lines
X-Git-Tag: v8.25~77
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5595024a2fdd726d88d57c5a06b633b752ef31db;p=thirdparty%2Fcoreutils.git

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.
---

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 7918aec6ab..88e16503d0 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