复习了tr 命令 写下加深印象

tr - translate or delete characters

 Translate, squeeze, and/or delete characters from standard input, writing to standard output.

 -c, -C, --complement
              first complement 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

tr 命令的格式：tr 选项 [集合1] [集合2]

-d 参数：删除文件中出现在集合一中的字符。

[useputty_login@PC_IN_LAN ~]$cat a
1aaaaaacc
2bbbbbbdd
[useputty_login@PC_IN_LAN ~]$tr -d [1] < a（删除了1）
aaaaaacc
2bbbbbbdd

-s 参数：压缩文件中在集合1中出现的字符

[useputty_login@PC_IN_LAN ~]$cat a
1aaaaaacc
2bbbbbbdd
[useputty_login@PC_IN_LAN ~]$tr -s [a] < a
1acc
2bbbbbbdd

用-s 选项删除空行

[useputty_login@PC_IN_LAN ~]$cat -A b
bbb$
$
$
ddd$
$
$
fff$
$
$
hhh$
[useputty_login@PC_IN_LAN ~]$tr -s "\n" < b
bbb
ddd
fff
hhh
首先我将文件理解成这样：

bbb\n\n\n

ddd\n\n\n

fff\n\n\n

hhh\n

因为-s 选项有压缩重复字符的作用，这里将\n压缩成每行一个，所以相当于去除空行。

-s 可以删除某些控制字符^M 思路是将结尾的控制字符替换为\n然后压缩

[useputty_login@PC_IN_LAN ~]$cat -A a
1aaaaaacc^M$
2bbbbbbdd^M$
[useputty_login@PC_IN_LAN ~]$tr -s "^M" "\n" < a
1aaaaaacc
2bbbbbbdd

[useputty_login@PC_IN_LAN ~]$tr -s "^M" "\n" < a > b
[useputty_login@PC_IN_LAN ~]$cat -A b
1aaaaaacc$
2bbbbbbdd$

-cs (-c -s)将集合1之外的替换成集合2中的字符，然后squeeze！

-t 参数：将文件中出现在集合1中的字符转换成集合2中出现得字符 一一对应转换。

[useputty_login@PC_IN_LAN ~]$cat a
1aaaaaacc
2bbbbbbdd

[useputty_login@PC_IN_LAN ~]$tr -t "a" "e" 1eeeeeecc
2bbbbbbdd

[useputty_login@PC_IN_LAN ~]$tr -t "ab" "e" 1eeeeeecc
2bbbbbbdd
-t 应该是默认选项

[useputty_login@PC_IN_LAN ~]$tr "a" "e" < a
1eeeeeecc
2bbbbbbdd

-c 就表示是集合1的补集

[useputty_login@PC_IN_LAN ~]$cat a
1aaaaaacc
2bbbbbbdd

[useputty_login@PC_IN_LAN ~]$tr -c "a\n" "e" < a （这里就是把文件中除a和换行符之外的所有字符都替换成e，应为每行文件末尾都有个换行符）
eaaaaaaee
eeeeeeeee