compgen, eval, export, file: move to common (#6508)

pages/common/file.md

@@ -0,0 +1,24 @@
+# file
+
+> Determine file type.
+> More information: <https://manned.org/file>.
+
+- Give a description of the type of the specified file. Works fine for files with no file extension:
+
+`file {{filename}}`
+
+- Look inside a zipped file and determine the file type(s) inside:
+
+`file -z {{foo.zip}}`
+
+- Allow file to work with special or device files:
+
+`file -s {{filename}}`
+
+- Don't stop at first file type match; keep going until the end of the file:
+
+`file -k {{filename}}`
+
+- Determine the mime encoding type of a file:
+
+`file -i {{filename}}`