Add Reference The Full Match In The Replacement as a Sed TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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@@ -1500,6 +1500,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [OSX sed Does Regex A Bit Different](sed/osx-sed-does-regex-a-bit-different.md)
 - [Output Only Lines Involved In A Substitution](sed/output-only-lines-involved-in-a-substitution.md)
 - [Reference A Capture In The Regex](sed/reference-a-capture-in-the-regex.md)
+- [Reference The Full Match In The Replacement](sed/reference-the-full-match-in-the-replacement.md)
 - [Use An Alternative Delimiter In A Substitution](sed/use-an-alternative-delimiter-in-a-substitution.md)
 
 ### Shell

sed/reference-the-full-match-in-the-replacement.md

@@ -0,0 +1,27 @@
+# Reference The Full Match In The Replacement
+
+The `&` can be used in the replacement part of a `sed` expression as reference
+to the string match for this iteration of the expression. The occurrence of `&`
+will be replaced with that entire match.
+
+As the `sed` man page puts it:
+
+> An ampersand (“&”) appearing in the replacement is replaced by the string
+> matching the RE.
+
+I made use of this recently with [a `sed` expression that was evaluating a list
+of filenames that I wanted to construct into a sequence of `mv`
+commands](unix/rename-a-bunch-of-files-by-constructing-mv-commands.md). I needed
+the filename that I was matching on to appear as the first argument of the `mv`
+command I was constructing.
+
+Here is what that looks like:
+
+```bash
+$ ls *.pdf |
+  sed 's/\(..\)\(..\)\(..\) Statement\.pdf/mv "&" "20\3-\1-\2-statement.pdf"/'
+```
+
+Notice right after `mv` in literal quotes is the `&`. That will be replaced in
+the resulting replacement with the full matching string of the regular
+expression in the first part of the sed statement (`s/<RE>/`).