Linux tr命令

在Linux系统中，tr命令用于对文件中的字符进行转换或删除操作。

该命令会从标准输入读取数据，在完成字符串的翻译处理后，将结果输出至标准输出。

命令格式

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

参数说明：

• -c, --complement：反向选择设定字符。即对符合 SET1 的字符不做处理，仅对不符合的部分进行转换
• -d, --delete：删除指定字符
• -s, --squeeze-repeats：将连续重复的字符压缩为单个指定字符
• -t, --truncate-set1：截断 SET1 的范围，使其长度与 SET2 一致
• --help：显示帮助信息
• --version：查看程序版本信息

字符集合支持的表达方式：

• \NNN 八进制值表示的字符 NNN (1 至 3 位数字)
• \\ 反斜杠符号
• \a Ctrl-G 铃声控制符
• \b Ctrl-H 退格符
• \f Ctrl-L 换页符
• \n Ctrl-J 换行符
• \r Ctrl-M 回车符
• \t Ctrl-I tab键
• \v Ctrl-X 水平制表符
• CHAR1-CHAR2 ：定义从 CHAR1 到 CHAR2 的字符范围（按ASCII顺序，只能从小到大）
• [CHAR*] ：SET2 特有语法，表示重复CHAR直到与SET1长度相同
• [CHAR*REPEAT] ：SET2 特有语法，表示将CHAR重复 REPEAT 次（REPEAT 使用八进制计数，以 0 开始）
• [:alnum:] ：所有字母和数字
• [:alpha:] ：所有字母
• [:blank:] ：所有水平空白字符
• [:cntrl:] ：所有控制字符
• [:digit:] ：所有数字
• [:graph:] ：所有可打印字符（不含空格）
• [:lower:] ：所有小写字母
• [:print:] ：所有可打印字符（含空格）
• [:punct:] ：所有标点符号
• [:space:] ：所有空白符（包括垂直和水平）
• [:upper:] ：所有大写字母
• [:xdigit:] ：所有十六进制数字
• [=CHAR=] ：匹配指定字符（等号内的CHAR可自定义）

示例演示

要将testfile文件中的小写字母全部转换为大写形式，可以执行以下命令：

cat testfile |tr a-z A-Z 

testfile原始内容如下：

$ cat testfile         #testfile原始内容  
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. 

经过tr命令转换后的输出结果为：

$ cat testfile | tr a-z A-Z #大小写转换结果  
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,  
FROM 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. 

除了使用a-z/A-Z直接映射外，还可以通过字符类实现大小写转换。例如：

cat testfile |tr [:lower:] [:upper:] 

输出效果完全一致：

$ cat testfile | tr [:lower:] [:upper:] #转换结果展示  
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,  
FROM 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.