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Linux shell tr 命令用于转换或删除文件中的字符。

tr 命令从标准输入设备读取数据，经过字符串转译后，将结果输出到标准输出设备。

tr 命令语法格式

tr [-cdst][--help][--version][第一字符集][第二字符集]  
tr [OPTION]…SET1[SET2]

参数说明

-c, --complement：反选设定字符。也就是符合 SET1 的部份不做处理，不符合的剩余部份才进行转换
-d, --delete：删除指令字符
-s, --squeeze-repeats：缩减连续重复的字符成指定的单个字符
-t, --truncate-set1：削减 SET1 指定范围，使之与 SET2 设定长度相等
--help：显示程序用法信息
--version：显示程序本身的版本信息

字符集合的范围：

--version\NNN 八进制值的字符 NNN (1 to 3 为八进制值的字符)
- \ 反斜杠
- \a Ctrl-G 铃声
- \b Ctrl-H 退格符
- \f Ctrl-L 走行换页
- \n Ctrl-J 新行
- \r Ctrl-M 回车
- \t Ctrl-I tab键
- \v Ctrl-X 水平制表符
- CHAR1-CHAR2

字符范围从 CHAR1 到 CHAR2 的指定，范围的指定以 ASCII 码的次序为基础，只能由小到大，不能由大到小。

[CHAR*] ：这是 SET2 专用的设定，功能是重复指定的字符到与 SET1 相同长度为止
[CHAR*REPEAT] ：这也是 SET2 专用的设定，功能是重复指定的字符到设定的 REPEAT 次数为止(REPEAT 的数字采 8 进位制计算，以 0 为开始)
[:alnum:] ：所有字母字符与数字
[:alpha:] ：所有字母字符
[:blank:] ：所有水平空格
[:cntrl:] ：所有控制字符
[:digit:] ：所有数字
[:graph:] ：所有可打印的字符(不包含空格符)
[:lower:] ：所有小写字母
[:print:] ：所有可打印的字符(包含空格符)
[:punct:] ：所有标点字符
[:space:] ：所有水平与垂直空格符
[:upper:] ：所有大写字母
[:xdigit:] ：所有 16 进位制的数字
[=CHAR=] ：所有符合指定的字符(等号里的 CHAR，代表你可自订的字符)

范例

假设存在 demo.txt 文件，内容如下

[root@localhost ~]# cat demo.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.

使用 tr 命令大小写转换后，得到如下输出结果：

[root@localhost ~]# cat demo.txt | tr a-z A-Z
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.

大小写转换，也可以通过 [:lower] [:upper] 参数来实现

[root@localhost ~]# cat demo.txt | tr [:lower:] [:upper:] #转换后的输出  
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.

标题：Linux shell tr 命令

tr 命令语法格式

参数说明

字符集合的范围：

范例

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