将具有命令替换功能的sed输出存储到变量中

Question

Consider a string

Message="Hello WoRld"

I would like to substitute the upper case R by the lower case r

echo "$Message" > file.txt
NewMessage=$(sed 's/R/r/' file.txt)

works fine! The following would work as well

NewMessage=$(echo ${Message} | sed 's/R/r/')

But my first reflex was to use command substitution

NewMessage=$(sed 's/R/r/' <("$Message"))

but it does not work. Why doesn't it work?

Answer 1

your cmd-sub version was missing the leading M ?

But you want

NewMessage=$(sed 's/R/r/' <(echo "$Message"))

OR your shell may support

NewMessage=$(sed 's/R/r/' <<< "$Message")

---

edit

and the simplest, most widely supported solution would be much simpler

NewMessage=$(echo "$Message" | sed 's/R/r/') 

If you need absolute stone-age compatibility to Bourne Shell (true /bin/sh ) then you'll have to forego the nice $(..cmdSub) syntax and use back-quotes for command-substitution:

NewMessage=`echo "$Message" | sed 's/R/r/'` 

IHTH

Answer 2

如果您使用的是bash 4，则不需要sed ：

NewMessage=${Message,,R}