Add Grab The First Line Of A File as a sed til

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_1112 TILs and counting..._
+_1113 TILs and counting..._
 
 ---
 
@@ -959,6 +959,7 @@ _1112 TILs and counting..._
 - [Equivalence Classes Of Repetition MetaChars](sed/equivalence-classes-of-repetition-metachars.md)
 - [Extract Value From Command Output With Sed](sed/extract-value-from-command-output-with-sed.md)
 - [Grab All The Method Names Defined In A Ruby File](sed/grab-all-the-method-names-defined-in-a-ruby-file.md)
+- [Grab The First Line Of A File](sed/grab-the-first-line-of-a-file.md)
 - [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)

sed/grab-the-first-line-of-a-file.md

@@ -0,0 +1,29 @@
+# Grab The First Line Of A File
+
+You can grab the first line of a file with `sed` using either the `p` (print)
+command or the `d` (delete) command.
+
+First, the _print_ command can be told to print the line matching the line
+number `1`. That combined with the `-n` flag, which suppresses all lines not
+explicitly printed, will print just the first line in the file.
+
+```bash
+$ sed '1 p' README.md
+# TIL
+```
+
+Second, the _delete_ command can be told to delete all lines that aren't the
+first (`1`) line.
+
+```bash
+$ sed '1! d' README.md
+# TIL
+```
+
+The `1` will match on the first line. By following it with `!`, that will
+negate it so that it represents all lines except `1`.
+
+See `man sed` for more details.
+
+Note: there are more efficient ways, not using `sed`, to get the first line in
+a file. This is an exercise in using and understanding some `sed` features.