Pipes实现LeetCode(195.第十行)
[LeetCode] 195.Tenth Line 第十行
How would you print just the 10th line of a file?
For example, assume that file.txt has the following content:
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10
Your script should output the tenth line, which is:
Line 10
Hint:
1. If the file contains less than 10 lines, what should you output?
2. There's at least three different solutions. Try to explore all possibilities.
这道题让我们用Bash脚本来打印一个txt文件的第十行,可以用很多种方法来实现,我们先来看一种是用awk来实现的方法,awk是强大的文本分析工具,具有流控制、数学运算、进程控制、内置的变量和函数、循环和判断的功能。其中NR表示行数,$0表示当前记录,所以我们可以用if来判断行数为第十行时,将内容打印出来即可:
解法一:
awk '{if(NR == 10) print $0}' file.txt
我们也可以用更简洁的写法来打印出第十行如下:
解法二:
awk 'NR == 10' file.txt
我们也可以使用流编辑工具sed来做。-n默认表示打印所有行,p限定了具体打印的行数:
解法三:
sed -n 10p file.txt
我们也可以使用tail和head关键字来打印。其中head表示从头开始打印,tail表示从结尾开始打印,-你表示根据文件行数进行打印,一些区别与联系请见下列例子:
tail -n 3 file.txt: 打印file文件的最后三行内容
tail -n +3 file.txt: 从file文件第三行开始打印所有内容
head -n 3 file.txt: 打印file文件的前三行
head -n -3 file.txt: 打印file文件除了最后三行的所有内容
至于竖杠|为管道命令,用法: command 1 | command 2 他的功能是把第一个命令command1执行的结果作为command 2的输入传给command 2。了解了这些知识,那么下面一行命令就很好理解了,首先输入file文件从第十行开始的所有内容,然后将输出内容的第一行打印出来即为第十行:
解法四:
tail -n +10 file.txt | head -n 1
下面这种方法跟上面刚好相反,先输出file文件的前十行,然后从输出的第十行开始打印,那么也能正好打印第十行的内容:
解法五:
head -n 10 file.txt | tail -n +10
参考资料:
https://leetcode.com/discuss/29526/super-simple-solution
https://leetcode.com/discuss/29591/simple-solution-using-awk
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