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+====== 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]]

GNU screen

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