字符集合的范圍：
\NNN 八進制值的字符 NNN (1 to 3 為八進制值的字符)
\\ 反斜杠
\a Ctrl-G 鈴聲
\b Ctrl-H 退格符
\f Ctrl-L 走行換頁
\n Ctrl-J 新行
\r Ctrl-M 回車
\t Ctrl-I tab鍵
\v Ctrl-X 水平制表符
CHAR1-CHAR2 ：字符范圍從 CHAR1 到 CHAR2 的指定，范圍的指定以 ASCII 碼的次序為基礎，只能由小到大，不能由大到小。
[CHAR*] ：這是 SET2 專用的設定，功能是重復指定的字符到與 SET1 相同長度為止
[CHAR*REPEAT] ：這也是 SET2 專用的設定，功能是重復指定的字符到設定的 REPEAT 次數為止(REPEAT 的數字采 8 進位制計算，以 0 為開始)
[:alnum:] ：所有字母字符與數字
[:alpha:] ：所有字母字符
[:blank:] ：所有水平空格
[:cntrl:] ：所有控制字符
[:digit:] ：所有數字
[:graph:] ：所有可打印的字符(不包含空格符)
[:lower:] ：所有小寫字母
[:print:] ：所有可打印的字符(包含空格符)
[:punct:] ：所有標點字符
[:space:] ：所有水平與垂直空格符
[:upper:] ：所有大寫字母
[:xdigit:] ：所有 16 進位制的數字
[=CHAR=] ：所有符合指定的字符(等號里的 CHAR，代表你可自訂的字符)
實例
將文件testfile中的小寫字母全部轉換成大寫字母，此時，可使用如下命令：
cat testfile |tr a-z A-Z
testfile文件中的內容如下：
$ cat testfile #testfile原來的內容 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.
使用 tr 命令大小寫轉換后，得到如下輸出結果：
$ cat testfile | tr a-z A-Z #轉換后的輸出 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, 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.
大小寫轉換，也可以通過[:lower][:upper]參數來實現。例如使用如下命令：
cat testfile |tr [:lower:] [:upper:]
輸出結果如下：
$ cat testfile | tr [:lower:] [:upper:] #轉換后的輸出 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, 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.
刪除Windows文件“造成”的’^M’字符
cat $file_name | tr -d "\r"
刪除連續的字符
echo "hhhhhh" | tr -s [:alnum:]