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.