大小写转换
将文件file.txt的小写字母转换成大写
1. 使用tr
cat file.txt | tr a-z A-Z
2. 使用sed
sed ‘y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/’ file.txt
sed的 y/source/dest/ Transliterate the characters in the pattern space which appear in source to the corresponding character in dest.
