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### 1.2 Controlling `ar` with a Script

    ar -M [ <script ]

If you use the single command-line option ‘`-M`’ with `ar`, you can control its operation with a rudimentary command language. This form of `ar` operates interactively if standard input is coming directly from a terminal. During interactive use, `ar` prompts for input (the prompt is ‘`AR >`’), and continues executing even after errors. If you redirect standard input to a script file, no prompts are issued, and `ar` abandons execution (with a nonzero exit code) on any error.

The `ar` command language is not designed to be equivalent to the command-line options; in fact, it provides somewhat less control over archives. The only purpose of the command language is to ease the transition to GNU `ar` for developers who already have scripts written for the MRI “librarian” program.

The syntax for the `ar` command language is straightforward:

- commands are recognized in upper or lower case; for example, `LIST` is the same as `list`. In the following descriptions, commands are shown in upper case for clarity.
- a single command may appear on each line; it is the first word on the line.
- empty lines are allowed, and have no effect.
- comments are allowed; text after either of the characters ‘`*`’ or ‘`;`’ is ignored.
- Whenever you use a list of names as part of the argument to an `ar` command, you can separate the individual names with either commas or blanks. Commas are shown in the explanations below, for clarity.
- ‘`+`’ is used as a line continuation character; if ‘`+`’ appears at the end of a line, the text on the following line is considered part of the current command.

Here are the commands you can use in `ar` scripts, or when using `ar` interactively. Three of them have special significance:

`OPEN` or `CREATE` specify a current archive, which is a temporary file required for most of the other commands.

`SAVE` commits the changes so far specified by the script. Prior to `SAVE`, commands affect only the temporary copy of the current archive.

`ADDLIB archive`
`ADDLIB archive (module, module, … module)`

  Add all the contents of archive (or, if specified, each named module from archive) to the current archive.

  Requires prior use of `OPEN` or `CREATE`.

`ADDMOD member, member, … member`

  Add each named member as a module in the current archive.

  Requires prior use of `OPEN` or `CREATE`.

`CLEAR`

  Discard the contents of the current archive, canceling the effect of any operations since the last `SAVE`. May be executed (with no effect) even if no current archive is specified.

`CREATE archive`

  Creates an archive, and makes it the current archive (required for many other commands). The new archive is created with a temporary name; it is not actually saved as archive until you use `SAVE`. You can overwrite existing archives; similarly, the contents of any existing file named archive will not be destroyed until `SAVE`.

`DELETE module, module, … module`

  Delete each listed module from the current archive; equivalent to ‘`ar -d archive module … module`’.

  Requires prior use of `OPEN` or `CREATE`.

`DIRECTORY archive (module, … module)`
`DIRECTORY archive (module, … module) outputfile`

  List each named module present in archive. The separate command `VERBOSE` specifies the form of the output: when verbose output is off, output is like that of ‘`ar -t archive module…`’. When verbose output is on, the listing is like ‘`ar -tv archive module…`’.

  Output normally goes to the standard output stream; however, if you specify outputfile as a final argument, `ar` directs the output to that file.

`END`

  Exit from `ar`, with a `0` exit code to indicate successful completion. This command does not save the output file; if you have changed the current archive since the last `SAVE` command, those changes are lost.

`EXTRACT module, module, … module`

  Extract each named module from the current archive, writing them into the current directory as separate files. Equivalent to ‘`ar -x archive module…`’.

  Requires prior use of `OPEN` or `CREATE`.

`LIST`

  Display full contents of the current archive, in “verbose” style regardless of the state of `VERBOSE`. The effect is like ‘`ar tv archive`’. (This single command is a GNU `ar` enhancement, rather than present for MRI compatibility.)

  Requires prior use of `OPEN` or `CREATE`.

`OPEN archive`

  Opens an existing archive for use as the current archive (required for many other commands). Any changes as the result of subsequent commands will not actually affect archive until you next use `SAVE`.

`REPLACE module, module, … module`

  In the current archive, replace each existing module (named in the `REPLACE` arguments) from files in the current working directory. To execute this command without errors, both the file, and the module in the current archive, must exist.

  Requires prior use of `OPEN` or `CREATE`.

`VERBOSE`

  Toggle an internal flag governing the output from `DIRECTORY`. When the flag is on, `DIRECTORY` output matches output from ‘`ar -tv` ’….

`SAVE`

  Commit your changes to the current archive, and actually save it as a file with the name specified in the last `CREATE` or `OPEN` command.

  Requires prior use of `OPEN` or `CREATE`.

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