====== exec ======

===== Default Keybindings =====

None.

===== Syntax =====

  * ''**exec** %%[[%%//fdpat//] //newcommand// [//args// //...//]]''

===== Description =====

Run a unix subprocess (specified by an executable path //newcommand// and
its optional arguments) in the current window.  The flow of data between
//newcommand//'s stdin/stdout/stderr, the process originally started in
the window (let us call it "application-process") and ''screen'' itself
(window) is controlled by the file descriptor pattern //fdpat//.  This
pattern is basically a three character sequence representing stdin, stdout
and stderr of newcommand.  A dot (''.'')  connects the file descriptor to
''screen''.  An exclamation mark (''!'') causes the file descriptor to be
connected to the application-process.  A colon ('':'')  combines both.
User input will go to //newcommand// unless //newcommand// receives the
application-process' output (//fdpat//'s first character is ''!'' or
'':'') or a pipe symbol (''|'') is added (as a fourth character) to the
end of //fdpat//.

Invoking ''exec'' without arguments shows name and arguments of the
currently running subprocess in this window.  Only one subprocess a time
can be running in each window.  When a subprocess is running the
''[[kill]]'' command will affect it instead of the window's process.

Refer to the postscript file {{:commands:fdpat.ps}} for a confusing illustration
of all 21 possible combinations.  Each drawing shows the digits 2,1,0
representing the three file descriptors of newcommand.  The box marked "W"
is the usual pty that has the application-process on its slave side.  The
box marked "P" is the secondary pty that now has ''screen'' at its master
side.

=== Abbreviations ===

Whitespace between the word ''exec'' and //fdpat// and the command can be
omitted.  Trailing dots and a //fdpat// consisting only of dots can be
omitted.  A simple "''|''" is synonymous for the pattern "''!..|''"; the
word ''exec'' can be omitted here and can always be replaced by "''!''".

===== Examples =====

<code>
exec ... /bin/sh
exec /bin/sh
!/bin/sh
</code>

Creates another shell in the same window, while the original shell is
still running.  Output of both shells is displayed and user input is sent
to the new ''/bin/sh''.

<code>
exec !.. stty 19200
exec ! stty 19200
!!stty 19200
</code>

Set the speed of the window's tty.  If your ''stty'' command operates on
stdout, then add another "''!''".

<code>
exec !..| less
|less
</code>

This adds a pager to the window output.  The special character ''|'' is
needed to give the user control over the pager although it gets its input
from the window's process.  This works, because ''less'' listens on stderr
(a behavior that ''screen'' would not expect without the ''|'') when its
stdin is not a tty.  Less versions newer than 177 fail miserably here;
good old ''pg'' still works.

<code>
!:sed -n s/.*Error.*/\007/p
</code>

Sends window output to both the user and the ''sed'' command.  The ''sed''
inserts an additional bell character (oct.  007) to the window output seen
by ''screen''.  This will cause "Bell in window //x//" messages, whenever
the string "Error" appears in the window.

===== See Also =====

  * [[:Misc]]