a (Add) command

Adds files to archive.

Examples

7z a archive1.zip subdir\

adds all files and subfolders from folder subdir to archive archive1.zip. The filenames in archive will contain subdir\ prefix.

7z a archive2.zip .\subdir\*

adds all files and subfolders from folder subdir to archive archive2.zip. The filenames in archive will not contain subdir\ prefix.

cd /D c:\dir1\
7z a c:\archive3.zip dir2\dir3\ 

7z a Files.7z *.txt -r

adds all *.txt files from current folder and its subfolders to archive Files.7z.

Notes

7-Zip doesn't uses the system wildcard parser. 7-Zip doesn't follow the archaic rule by which *.* means any file. 7-Zip treats *.* as matching the name of any file that has an extension. To process all files, you must use a * wildcard.

Switches that can be used with this command

-i (Include)
-m (Method)
-p (Set Password)
-r (Recurse)
-sfx (create SFX)
-si (use StdIn)
-so (use StdOut)
-ssw (Compress shared files)
-t (Type of archive)
-u (Update)
-v (Volumes)
-w (Working Dir)
-x (Exclude)

See also

Commands: d (Delete), u (Update)
Switches: -u (Update)