sponge: add page (#4117)

pages/common/sponge.md

@@ -0,0 +1,12 @@
+# sponge
+
+> Soak up the input before writing the output file.
+> More information: <https://linux.die.net/man/1/sponge>.
+
+- Append file content to the source file:
+
+`cat {{path/to/file}} | sponge -a {{path/to/file}}`
+
+- Remove all lines starting with # in a file:
+
+`grep -v '^{{#}}' {{path/to/file}} | sponge {{path/to/file}}`