Replacing some uppercase characters with a lowercase character using sed

Question

I have a file with a name file.txtthat contains absolute paths. It looks like this:

J:/Folder/inner
J:/Folder/inner2

At first I wanted to write a bash script that replaces J:/with /cygdrive/j/. So I did it like this:

sed -i 's/J:\//\/cygdrive\/j\//g' file.txt                    

and works as expected.
But now I need something more sophisticated: the absolute paths do not need to begin with J- they can start with a C, D, E...
I want to do the same as above, only because I do not know what will be the first letter. For example: it C:/Folder/innerwill become /cygdrive/c/Folder/inner, but it D:/Folder/innerwill become /cygdrive/d/Folder/inner.
I understand that I need to use regex to achieve this, but I have not found a way to do this. Do you know how I can get what I want?

Answer 1

sed, , GNU sed. ,

$ cat file.txt 
J:/Folder/inner
J:/Folder/inner2
C:/Folder/inner
D:/Folder/inner

$ sed -E 's#^(.):#/cygdrive/\l\1#' file.txt 
/cygdrive/j/Folder/inner
/cygdrive/j/Folder/inner2
/cygdrive/c/Folder/inner
/cygdrive/d/Folder/inner

• -E, ERE, ()
  • -r -E
• ^(.): :
  • ^([A-Z]): ^([A-Za-z]): ,
• /cygdrive/\l\1 /cygdrive/
• # -, / /
  • , \,
• -i ,

Answer 2

Awk tolower() , , :

awk -F: '{print "/cygdrive/"tolower($1)""$2}' file.txt

$1 (J) $2 ( ). "" - . .

, ,

awk -F: '{print "/cygdrive/"tolower($1)""$2}' file.txt > temp && mv temp file.txt

J:/Folder/inner
J:/Folder/inner2
C:/Folder/inner
D:/Folder/inner

/cygdrive/j/Folder/inner
/cygdrive/j/Folder/inner2
/cygdrive/c/Folder/inner
/cygdrive/d/Folder/inner

---

perl, ,

perl -lne 'print "/cygdrive/\L$1$2" if /(.):(.+)/' file.txt