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diff --git a/src/tools/README.md b/src/tools/README.md
index 0b1666c..2aa2f5c 100644
--- a/src/tools/README.md
+++ b/src/tools/README.md
@@ -16,3 +16,4 @@
 - [dot](./dot.md)
 - [ffmpeg](./ffmpeg.md)
 - [column](./column.md)
+- [sort](./sort.md)
diff --git a/src/tools/sort.md b/src/tools/sort.md
new file mode 100644
index 0000000..e74b490
--- /dev/null
+++ b/src/tools/sort.md
@@ -0,0 +1,35 @@
+# sort(1)
+
+```
+sort [opts] [file]
+  opts:
+    -r      reverse output
+    -b      ignore leading blanks
+
+    -n      sort by numeric
+    -h      sort by human numeric
+    -V      sort by version
+
+    -k<N>  sort by Nth key
+    -t<S>  field separator
+```
+
+## Examples
+```sh
+# Sort by directory sizes.
+du -sh * | sort -h
+```
+
+```sh
+# Sort numeric by second key.
+# The default key separator is non-blank to blank transition.
+echo 'a 4
+d 10
+c 21' | sort -k2 -n
+
+# Sort numeric by second key, split at comma.
+echo 'a,4
+d,10
+c,21' | sort -k2 -n -t,
+```
+> Use `--debug` to annotate part of the line used to sort and hence debug the key usage.