Linux shell cat 命令
Linux shell cat 命令用于连接文件并将内容输出到标准输出设备上。
使用权限
所有可用户
cat 命令语法格式
cat [-AbeEnstTuv] [--help] [--version] fileName
参数
-n , --number ：由 1 开始对所有输出的行数编号。
-b , --number-nonblank ：和 -n 相似，只不过对于空白行不编号。
-s , --squeeze-blank ：当遇到有连续两行以上的空白行，就代换为一行的空白行。
-v , --show-nonprinting ：使用 ^ 和 M- 符号，除了 LFD 和 TAB 之外。
-E , --show-ends : 在每行结束处显示 $。
-T , --show-tabs : 将 TAB 字符显示为 ^I。
-e : 等价于 -vE。
-A, --show-all ：等价于 -vET。
-e： 等价于"-vE"选项；
-t： 等价于"-vT"选项；
范例
将 demo1.txt 的文件内容加上行号后输出到 demo2.txt 这个文件中
demo1.txt 文件内容
[root@localhost ~]# cat demo1.txt Linux networks are becoming more and more common, but scurity is often an overlooked issue. Unfortunately, in today’s environment all networks are potential hacker targets, fro0m tp-secret military research networks to small home LANs. Linux Network Securty focuses on securing Linux in a networked environment, where the security of the entire network needs to be considered rather than just isolated machines. It uses a mix of theory and practicl techniques to teach administrators how to install and use security applications, as well as how the applcations work and why they are necesary.
将 demo1.txt 的文件内容加上行号后输出到 demo2.txt 这个文件
[root@localhost ~]# cat -n demo1.txt > demo2.txt
demo2.txt 文件中的内容
[root@localhost ~]# cat demo2.txt 1 Linux networks are becoming more and more common, but scurity is often an overlooked 2 issue. Unfortunately, in today’s environment all networks are potential hacker targets, 3 fro0m tp-secret military research networks to small home LANs. 4 Linux Network Securty focuses on securing Linux in a networked environment, where the 5 security of the entire network needs to be considered rather than just isolated machines. 6 It uses a mix of theory and practicl techniques to teach administrators how to install and 7 use security applications, as well as how the applcations work and why they are necesary. [root@localhost ~]#
把文件 demo1.txt 和 demo2.txt 的内容加上行号（空白行不加）之后将内容 附加 到 demo3.txt 文件中：
[root@localhost ~]# cat -b demo1.txt demo2.txt >> demo3.txt
清空 /etc/test.txt 文件内容
[root@localhost ~]# cat /dev/null > /etc/test.txt
cat 也可以用来制作镜像文件
cat 命令可以制作软盘的镜像文件，将软盘放好后输入
[root@localhost ~]# cat /dev/fd0 > OUTFILE
相反的，如果想把 image file 写到软盘，输入：
[root@localhost ~]# cat IMG_FILE > /dev/fd0
注意
- OUTFILE 指输出的镜像文件名
- IMG_FILE 指镜像文件
- 若从镜像文件写回 device 时，device 容量需与相当
- 通常用制作开机磁片