概述
使用tr命令可以对输入的字符串的字符进行替换、压缩和删除(使用-d选项)，需要注意的是，每个替换行为是根据原字符串进行的,也可以理解成是同时一一替换，而不是等待第一个字符替换完了再替换下一个。下图说明
image
# echo "helloc,world" | tr 'lo' 'oe' //l替换o后，那候些替换过来的o不会替换为e
heooec,werod
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：
- 字符集1：指定要转换或删除的原字符集。当执行转换操作时，必须使用参数“字符集2”指定转换的目标字符集。但执行删除操作时，不需要参数“字符集2”；
- 字符集2：指定要转换成的目标字符集。
'A-Z' 和 'a-z'都是集合，集合是可以自己制定的，例如：'ABD-}'、'bB.,'、'a-de-h'、'a-c0-9'都属于集合，集合里可以使用'\n'、'\t'，可以可以使用其他ASCII字符。
- -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,然后SET1中的字符替换成SET2字符
实例
删除数字
# echo "1234abcd" | tr -d [:digit:]
abcd
删除特定字符
# echo "1234567843ab,cd" | tr -d 34
125678ab,cd
反向删除
# echo "1234567843ab,cd" | tr -Cd 34
3443
将制表符转换为空格
cat text | tr '\t' ' '
缩减连续重复的字符成指定的单个字符
# echo "123333a4444ab,cd" | tr -s 34 zs //将连续的3和4分别替换成单个z好s
12zasab,cd
小写转大写
# echo "hello,world" | tr a-z A-Z
HELLO,WORLD
# echo "hello,world" | tr [:lower:] [:upper:]
HELLO,WORLD
# echo "hello,world" | tr a-z A-Z
HELLO,WORLD
# echo "hello,world" | tr [:lower:] [:upper:]
HELLO,WORLD
删除Windows文件“造成”的'^M'字符
cat file | tr -s "\r" "\n" > new_file
或
cat file | tr -d "\r" > new_file
# echo "helloc,world" | tr -t 'lowc' 'oe' //将lowc截断成lo，然后将字符串中l替换成o,o替换成e，需要注意的是，每个替换行为是根据原字符进行的
heooec,werod
tr --help
Usage: tr [OPTION]... SET1 [SET2]
Translate, squeeze, and/or delete characters from standard input,
writing to standard output.
-c, -C, --complement use the complement of SET1
-d, --delete delete characters in SET1, do not translate
-s, --squeeze-repeats replace each input sequence of a repeated character
that is listed in SET1 with a single occurrence
of that character
-t, --truncate-set1 first truncate SET1 to length of SET2
--help display this help and exit
--version output version information and exit
SETs are specified as strings of characters. Most represent themselves.
Interpreted sequences are:
\NNN character with octal value NNN (1 to 3 octal digits)
\\ backslash
\a audible BEL
\b backspace
\f form feed
\n new line
\r return
\t horizontal tab
\v vertical tab
CHAR1-CHAR2 all characters from CHAR1 to CHAR2 in ascending order
[CHAR*] in SET2, copies of CHAR until length of SET1
[CHAR*REPEAT] REPEAT copies of CHAR, REPEAT octal if starting with 0
[:alnum:] all letters and digits
[:alpha:] all letters
[:blank:] all horizontal whitespace
[:cntrl:] all control characters
[:digit:] all digits
[:graph:] all printable characters, not including space
[:lower:] all lower case letters
[:print:] all printable characters, including space
[:punct:] all punctuation characters
[:space:] all horizontal or vertical whitespace
[:upper:] all upper case letters
[:xdigit:] all hexadecimal digits
[=CHAR=] all characters which are equivalent to CHAR
Translation occurs if -d is not given and both SET1 and SET2 appear.
-t may be used only when translating. SET2 is extended to length of
SET1 by repeating its last character as necessary. Excess characters
of SET2 are ignored. Only [:lower:] and [:upper:] are guaranteed to
expand in ascending order; used in SET2 while translating, they may
only be used in pairs to specify case conversion. -s uses SET1 if not
translating nor deleting; else squeezing uses SET2 and occurs after
translation or deletion.
GNU coreutils online help: