fullscreen: don't fullscreen if stdout is not a tty.

* basta.sh (basta.fullscreen): Separate option parsing
from side effects an do it earlier. Recognize a new -f
option, separately or clumped with -s. If -f is not
supplied and standard output is not a TTY, then
just execute the command and return, without doing
full screen.

* README.md: Documented -f option.

2 files changed, 44 insertions, 12 deletions

diff --git a/README.md b/README.md
index 97f8abf..45d36ba 100644
--- a/README.md
+++ b/README.md
@@ -98,15 +98,25 @@ the full screen.
 Create `basta.fullscreen <program>` alias for each program that is to use
 the full terminal.
 
-The `basta.fullscreen` function takes a single option, `-s`. If that
-is specified, then then Basta will save and restore the terminal around
-the invocation of the program. This should only be used for full-screen
+The `basta.fullscreen` function takes two options, `-f` and `-s`.
+They can be used together, and may be specified separately in any order
+or clumped as `-fs` or `-sf`.
+
+The `-f` option will force full screen mode even if the function's
+standard output is redirected such that it is not a terminal.
+By default, if standard output is redirected, `basta.fullscreen`
+just executes the specified command without preparing full screen mode.
+The default behavior is sensible; it prevents a race condition between
+`basta.fullscreen` coming out of fullscreen mode and restoring the status line,
+and a subsequent pipeline element still running, concurrently producing output
+to the terminal, resulting in a messed-up display.
+
+If the `-s` option is used, then then Basta will save and restore the terminal
+around the invocation of the program. This should only be used for full-screen
 programs that don't output any messages outside of their full-screen paradigm,
-which should persist in the terminal window.
-
-The `top` utility is a good target for this. Some versions of `top` do not
-save and restore the screen, with with `basta.fullscreen -s top` we
-get that behavior:
+which should persist in the terminal window.  The `top` utility is a good
+target for this. Some versions of `top` do not save and restore the screen,
+with with `basta.fullscreen -s top` we get that behavior:
 
    ::text
    alias top='basta.fullscreen -s top'
diff --git a/basta.sh b/basta.sh
index b920abd..9dff193 100644
--- a/basta.sh
+++ b/basta.sh
@@ -313,22 +313,44 @@ basta.fullscreen()
   local exit=0
   local saveint=$(trap -p INT)
   local saveterm=
+  local force=
   local ttyfd
 
+  while true; do
+    case $1 in
+    ( -s )
+      saveterm=y
+      ;;
+    ( -f )
+      force=y
+      ;;
+    ( -sf | -fs )
+      saveterm=y
+      force=y
+      ;;
+    ( * )
+      break
+      ;;
+    esac
+    shift
+  done
+
+  if ! [ -t 1 ] && ! [ $force ] ; then
+    eval command $args
+    return $?
+  fi
+
   trap : INT
 
   exec {ttyfd}<>/dev/tty
 
-  if [ "$1" == "-s" ] ; then
-    shift
-    saveterm=y
+  if [ $saveterm ] ; then
     printf $'\e[?1049h' >&$ttyfd
   else
     basta_deferred_intr=WINCH
     printf $'\e[J' >&$ttyfd
   fi
 
-
   printf $'\e7\e[1;%sr\e8' $realrows >&$ttyfd
   stty rows $realrows <&$ttyfd