第四章：Tweaking Unix--31.显示带有行号的文件

   有许多种方法能够达到显示行号的目的，某些程序甚至很简短。好比能够用一个awk来实现：

awk '{print NR": "$0}' < inputfile

   一样，在某些Unix版本上，cat命令有-n选项，或是more(less, pg)也有能显示行号的选项。但还有一些Unix的版本上，可能这些都通通没有，那么此时，下面的这个简易脚本就能够发威了：

#!/bin/sh

# numberlines.sh -- 效果等同于cat -n命令

for filename
do
	linecount="1"
	while read line
	do
		echo "${linecount}: $line"
		linecount="$(($linecount+1))"
	done < $filename
done

exit 0

   这个脚本能够接受任意多的文件做为输入，可是不能经过管道给它提供输入。固然，如有须要能够修改下程序。
测试下脚本：

$ numberlines text.snippet.txt 
1: Perhaps one of the most valuable uses of shell scripts is to fix 
2: your particular flavor of Unix and make it more like other flavors, 
3: to bring your commands into conformance or to increase consistency 
4: across different systems. The outsider view of Unix suggests a 
5: nice, uniform command-line experience, helped along by the existence 
6: of and compliance with the POSIX standards for Unix. But anyone who's 
7: ever touched more than one computer knows how much they can vary 
8: within these broad parameters.

若是你有了一个标记出行号的文件，那么此时你就能够反转文件了：

cat -n filename | sort -nr | cut -c8-

上面的这行命令何时会颇有用呢？一个常常遇到的状况就是，你想显示一个日志文件的时候，