Detailed explanation of Linux shell tr command
Linux shell tr 命令详解
1. 用途
tr,translate的简写,主要用于压缩重复字符,删除文件中的控制字符以及进行字符转换操作。
2. 语法
tr [OPTION]... SET1 [SET2]
3. 参数
3.1 -s 压缩重复字符
-s: squeeze-repeats,用SET1指定的字符来替换对应的重复字符 (replace each input sequence of a repeated character that is listed in SET1 with a single occurrence of that character)
xiaosi@Qunar:~/test$ echo "aaabbbaacccfddd" | tr -s [abcdf] // abacfd
可以使用这一特点,删除文件中的空白行,实质上跟上面一样,都是用SET1指定的字符来替换对应的重复字符
xiaosi@Qunar:~/test$ cat b.txt I like football Football is very fun! Hello xiaosi@Qunar:~/test$ cat b.txt | tr -s ["\n"] I like football Football is very fun! Hello
3.2 -d 删除字符
-d:delete,删除SET1中指定的所有字符,不转换(delete characters in SET1, do not translate)
xiaosi@Qunar:~/test$ echo "a12HJ13fdaADff" | tr -d "[a-z][A-Z]" 1213 xiaosi@Qunar:~/test$ echo "a1213fdasf" | tr -d [adfs] 1213
3.3 字符替换
-t:truncate,将SET1中字符用SET2对应位置的字符进行替换,一般缺省为-t
xiaosi@Qunar:~/test$ echo "a1213fdasf" | tr -t [afd] [AFO] // A1213FOAsF
上述代码将a转换为A,f转换为F,d转换为O。
可以利用这一特点,实现大小字母的转换
xiaosi@Qunar:~/test$ echo "Hello World I Love You" |tr -t [a-z] [A-Z] HELLO WORLD I LOVE YOU xiaosi@Qunar:~/test$ echo "HELLO WORLD I LOVE YOU" |tr -t [A-Z] [a-z] hello world i love you
也可以利用字符集合进行转换
xiaosi@Qunar:~/test$ echo "Hello World I Love You" |tr -t [:lower:] [:upper:] HELLO WORLD I LOVE YOU xiaosi@Qunar:~/test$ echo "HELLO WORLD I LOVE YOU" |tr -t [:upper:] [:lower:] hello world i love you
备注:
字符集合如下
\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 从CHAR1 到 CHAR2的所有字符按照ASCII字符的顺序 [CHAR*] in SET2, copies of CHAR until length of SET1 [CHAR*REPEAT] REPEAT copies of CHAR, REPEAT octal if starting with 0 [:alnum:] 所有的字母和数字 [:alpha:] 所有字母 [:blank:] 水平制表符,空白等 [:cntrl:] 所有控制字符 [:digit:] 所有的数字 [:graph:] 所有可打印字符,不包括空格 [:lower:] 所有的小写字符 [:print:] 所有可打印字符,包括空格 [:punct:] 所有的标点字符 [:space:] 所有的横向或纵向的空白 [:upper:] 所有大写字母
3.4 字符补集替换
-c:complement,用SET2替换SET1中没有包含的字符
xiaosi@Qunar:~/test$ cat a.txt Monday 09:00 Tuesday 09:10 Wednesday 10:11 Thursday 11:30 Friday 08:00 Saturday 07:40 Sunday 10:00 xiaosi@Qunar:~/test$ cat a.txt | tr -c "[a-z][A-Z]" "#" | tr -s "#" | tr -t "#" "\n" Monday Tuesday Wednesday Thursday Friday Saturday Sunday
上面代码中 tr -c "[a-z][A-Z]" "#" 表示将除大小字母以外的所有的字符都替换为#。
上面代码可优化为:
xiaosi@Qunar:~/test$ cat a.txt | tr -cs "[a-z][A-Z]" "\n" Monday Tuesday Wednesday Thursday Friday Saturday Sunday
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