| Files | 1!: | 
| 1!:0 y | Directory. y is a string of the path 
search expression (a boxed string is also accepted); 
the result is a 5-column table of the file name, 
modification time, size, permission, and attributes, 
individually boxed.  For example, try 1!:0 '*.*'. 
The permission and attribute columns are system dependent.  
For example, in Windows: 1!:0 'j.exe' +-----+-----------------+------+---+------+ |j.exe|1998 2 2 14 33 46|676864|rwx|-----a| +-----+-----------------+------+---+------+Permission is a 3-letter string indicating the read, write, and execute permissions. Attributes is a 6-letter string indicating read-only, hidden, system, volume label, directory, and archive. | 
| 1!:1 y | Read. y is a file name or a file number 
(produced by 1!:21); the result is a string of the file contents., 
e.g. 1!:1 <'abc.q'. The following values 
for y are also permitted: 1 read from the keyboard (does not work within a script) 3 read from standard input (stdin) | 
| x 1!:2 y | Write. x is a string of the new contents 
of the file; y is a file name or file number 
(produced by 1!:21). The following values 
for y are also permitted: 2 screen output. 4 standard output (stdout) 5 standard error (stderr) | 
| x 1!:3 y | Append. Like x 1!:2 y, but appends rather than replaces | 
| 1!:4 y | Size | 
| 1!:5 y | Create Directory. y is a (boxed) directory name | 
| [x] 1!:6 y | Query/Set Attributes. | 
| [x] 1!:7 y | Query/Set Permissions. | 
| 1!:11 y | Indexed Read. y is a list of a boxed file name 
(or number) and a boxed index and length. The index may be negative. 
If the length is elided, the read goes to the end.  For example: 1!:11 'abc.x';1000 20 f=: 1!:21 <'abc.x' 1!:11 f,1000 20 | 
| x 1!:12 y | Indexed Write. x is the string to be written; y is a list of a boxed file name (or number) and a boxed index. | 
| 1!:20 y | File Numbers and Names. A 2-column table of the open file numbers and names. | 
| 1!:21 y | Open. Open file named y, creating it if necessary; result is a file number. | 
| 1!:22 y | Close. Close file named or numbered y. Any locks are released. | 
| 1!:30 y | Locks. A 3-column integer table of the file number, index, and length of file locks. The argument y is required but ignored. | 
| 1!:31 y | Lock. y is a 3-element integer vector of the file number, index, and length of the file region to be locked; the result is 1 if the request succeeded, and 0 if it did not. | 
| 1!:32 y | Unlock. y is a 3-element integer vector of the file number, index, and length of the file region to be unlocked. | 
| 1!:43 y | Query Current Working Directory. Query the current working directory (Posix getcwd). | 
| 1!:44 y | Set Current Working Directory. Set the current working directory (Posix chdir). | 
| 1!:46 y | Query DLL Path. Query the UTF8 path to j.dll in Windows and '' in Unix. | 
| 1!:55 y | Erase File/Directory. e.g., 1!:55<'careful' |