tr替换

tr替换：
tr 替换字符：被替换的字符与替换的字符数必须是相等的
用法：tr 旧字符 新字符

cat > a.txt <root:1:0:bin
bin:2:200:bash
jim:10:300:bash
tom:102:10:bash
bin:2:200:bash
EOF

cat a.txt | tr 20 89 将cat a.txt中的结果中的20替换成89
root:1:9:bin
bin:8:899:bash
jim:19:399:bash
tom:198:19:bash
bin:8:899:bash

cat a.txt | tr 'a-z' 'A-Z' 在替换的时候是一一对应的替换
ROOT:1:0:BIN
BIN:2:200:BASH
JIM:10:300:BASH
TOM:102:10:BASH
BIN:2:200:BASH

cat a.txt | tr 0-4 5-9
root:6:5:bin
bin:7:755:bash
jim:65:855:bash
tom:657:65:bash
bin:7:755:bash

\n 换行符
cat a.txt | tr "\n" "+" 将换行符换成+号
root:1:0:bin+bin:2:200:bash+jim:10:300:bash+tom:102:10:bash+bin:2:200:bash+

cat a.txt | tr -s "o0" 用-s把连续重复的字符替换成一个字符
rot:1:0:bin
bin:2:20:bash
jim:10:30:bash
tom:102:10:bash
bin:2:20:bash

echo >> a.txt 在a.txt文件中追加空白行,请执行3次

cat a.txt | tr -s "\n" 去掉空白行