Add notes on substitution with sed

sed.md

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+## Deleting lines matching a pattern containing slashes
+
+I want to delete a line from a file, matching a string.
+This is a simplified example.
+
+    $ string='a line with spaces and a $variable substitution'
+    $ echo $string
+    a line with spaces and a $variable substitution
+    $ echo $string > temp.txt
+    ~ $ sed "/$the_string/d" temp.txt
+    ~ $ 
+
+So far so good.
+
+However, the actual string in the real problem is this:
+`export PATH="$PATH:/home/mbexegc2/.local/share/hpcflow/links"`
+
+So I can't use forward slash as the delimiter without escaping all the slashes
+in the string.
+I thought I could just use a different delimiter (which I've done in the past with 
+sed (search/replace) substitutions).
+However, it doesn't work:
+
+    ~ $ sed "#$the_string#d" temp.txt
+    a line with spaces and a $variable substitution
+
+Turns out, you *can* use a different delimiter, but you need to escape it with a backslash
+at the start:
+
+    ~ $ sed "\#$the_string#d" temp.txt
+    ~ $ 
+
+