Linux Shell 脚本攻略 读书笔记 -- 201.cat的几种用法

cat可以读取、显示和拼接文件内容
1. 打印单个文件：
root@debian:/home/chicol/scripts# cat file.txt 
This is a line inside file.txt
This is second line inside file.txt
打印多个文件：
root@debian:/home/chicol/scripts# cat one.txt two.txt 
This is line from one.txt
This is line from two.txt
root@debian:/home/chicol/scripts# 
2. 读取标准输入：
root@debian:/home/chicol/scripts# ls | cat
1
1_12fname.sh
a1
a2
a3
calcu.sh
file.txt
functions.sh
ifs2.sh
ifs.sh
null
one.txt
out.txt
password.sh
printf.sh
sleep.sh
test1.sh
text.txt
three.txt
time_take.sh
tmp.txt
two.txt
将标准输入和文件内容拼接：
root@debian:/home/chicol/scripts# ls | cat - file.txt 
1
1_12fname.sh
a1
a2
a3
calcu.sh
file.txt
functions.sh
ifs2.sh
ifs.sh
null
one.txt
out.txt
password.sh
printf.sh
sleep.sh
test1.sh
text.txt
three.txt
time_take.sh
tmp.txt
two.txt
This is a line inside file.txt
This is second line inside file.txt
这里将"-"当作stdin文本的文件名。
3. cat打印文件内容的几个选项用法：
cat -s ：当文件中有连续空白行时，使用-s选项打印时，会去掉多余的空白行，只保留一个空白行
cat -n： 打印文件内容时显示行号
cat -T： 可以区别显示制表符和空格，制表符显示为“^I”
这里来看下这几个选项在一起使用的例子：

root@debian:/home/chicol/scripts# cat three.txt 
This is first line.


This is second line






This is third line.
        Tab line.
        Space line.
root@debian:/home/chicol/scripts# cat -snT three.txt 
     1  This is first line.
     2
     3  This is second line
     4
     5  This is third line.
     6  ^ITab line.
     7          Space line.
root@debian:/home/chicol/scripts#