如何在sed中使用Shell通配符？

Question

I'm trying to use a shell wildcard in sed. The following fails. (I expect foo as output.)

$ touch foo
$ ls
foo
$ echo *
foo
$ bar=*
$ echo $bar
foo
$ echo "$bar"
*
$ echo replace | sed "s/replace/${bar}/"
*
$ echo replace | sed "s/replace/"${bar}"/"
*

As expected, the penultimate command doesn't produce foo , since ${bar} is (double-)quoted. However, I expected the last command to expand the wildcard.

I can get either command to work after the following, though.

bar=$(echo *)

Further, I would have expected shell wildcard expansion in the following, which does not occur.

$ echo replace | sed s/replace/*/
*

However, this works.

$ echo replace | sed s/replace/$(echo *)/
qwe

Answer 1

Your last command does try to expand the wildcard except that it fails. From man bash :

 Pathname Expansion
        After  word  splitting,  unless  the -f option has been set, bash
        scans each word for the characters *, ?, and [.  If one of these
        characters appears, then the word is regarded as a pattern, and
        replaced with an alphabetically sorted list of file names matching
        the  pattern.

As it says, bash tries to expand each word containing a * to matching filenames. In your case, it tries to expand to a filename beginning with s/replace/ and there is no such file. To prove this:

$ echo "aaaa" | sed "s@a@*@g"
****

$ echo "aaaa" | sed "s@a@"*"@g"
****

$ touch s@a@b@g

$ echo "aaaa" | sed "s@a@*@g"
****

$ echo "aaaa" | sed "s@a@"*"@g"
bbbb

As for the solution to your problem, you can use subshell expansion as mentioned in the comments.