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.
