Add new "$_shell(CMD)" internal function

For testing a following patch, I wanted a way to send a SIGINT to GDB
from a breakpoint condition.  And I didn't want to do it from a Python
breakpoint or Python function, as I wanted to exercise non-Python code
paths.  So I thought I'd add a new $_shell internal function, that
runs a command under the shell, and returns the exit code.  With this,
I could write:

  (gdb) b foo if $_shell("kill -SIGINT $gdb_pid") != 0 || <other condition>

I think this is generally useful, hence I'm proposing it here.

Here's the new function in action:

 (gdb) p $_shell("true")
 $1 = 0
 (gdb) p $_shell("false")
 $2 = 1
 (gdb) p $_shell("echo hello")
 hello
 $3 = 0
 (gdb) p $_shell("foobar")
 bash: line 1: foobar: command not found
 $4 = 127
 (gdb) help function _shell
 $_shell - execute a shell command and returns the result.
 Usage: $_shell (command)
 Returns the command's exit code: zero on success, non-zero otherwise.
 (gdb)

NEWS and manual changes included.

Approved-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Tom Tromey <tom@tromey.com>
Approved-By: Eli Zaretskii <eliz@gnu.org>
Change-Id: I7e36d451ee6b428cbf41fded415ae2d6b4efaa4e

1 files changed, 10 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 8ac8292..75cd11b 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -68,6 +68,16 @@ maintenance info frame-unwinders
   List the frame unwinders currently in effect, starting with the highest
   priority.
 
+* New convenience function "$_shell", to execute a shell command and
+  return the result.  This lets you run shell commands in expressions.
+  Some examples:
+
+   (gdb) p $_shell("true")
+   $1 = 0
+   (gdb) p $_shell("false")
+   $2 = 1
+   (gdb) break func if $_shell("some command") == 0
+
 * MI changes
 
 ** mi now reports 'no-history' as a stop reason when hitting the end of the