### 5.9 Test case special variables ¶

There are special variables that contain other information from DejaGnu. Your test cases can inspect these variables, as well as the variables saved in `site.exp`. These variables should never be changed.

`$prms_id` ¶

  The bug tracking system (eg. PRMS/GNATS) number identifying a corresponding bug report (0 if you do not specify it).

`$bug_id` ¶

  An optional bug ID, perhaps a bug identification number from another organization (0 if you do not specify it).

`$subdir` ¶

  The subdirectory for the current test case.

`$exec_output` ¶

  This is the output from a `${tool}_load` command. This only applies to tools like GCC and GAS which produce an object file that must in turn be executed to complete a test.

`$comp_output` ¶

  This is the output from a `${tool}_start` command. This is conventionally used for batch-oriented programs, like GCC and GAS, that may produce interesting output (warnings, errors) without further interaction.

`$expect_out(buffer)` ¶

  The output from the last command. This is an internal variable set by Expect. More information can be found in the Expect manual.