posts:script: write up the terminal-recording utility

diff --git a/posts/Screen_recording.mdwn b/posts/Screen_recording.mdwn
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+++ b/posts/Screen_recording.mdwn
@@ -1,9 +1,10 @@
 I've been learning about screen recording in Linux so I can make a
 demo/tutorial for [[Hooke]].  There seem to be a number of options
 ([Xvidcap][], [recordMyDesktop][], etc.), but my favorite approach is
-to use [ffmpeg][] directly from the command line.  You may recall
-ffmpeg from my earlier post about [[video encoding|video]].  For those
-to lazy to read the man page, here are some highlights:
+to use [ffmpeg][] directly from the command line (If you're only
+interested in recording terminal sessions, look at [[script]]).  You
+may recall ffmpeg from my earlier post about [[video encoding|video]].
+For those to lazy to read the man page, here are some highlights:
 
 Record audio:
 

diff --git a/posts/script.mdwn b/posts/script.mdwn
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+`script` is a nice utility for recording terminal sessions.  It spawns
+a new shell (by default), and records any activity in that shell:
+
+    $ script /tmp/script
+    Script started, file is /tmp/script
+    $ ps -u wking | grep script
+    12102 pts/7    00:00:00 script
+    12103 pts/7    00:00:00 script
+    $ pstree 12102
+    script───script───bash───pstree
+    $ exit
+    exit
+    Script done, file is /tmp/script
+
+The recorded file stores all the characters sent to the terminal:
+
+    $ cat -v /tmp/script
+    Script started on Mon 10 Dec 2012 08:07:17 AM EST
+    ^[]0;wking@mjolnir:~^G^[[?1034h^[[01;32mwking@mjolnir^[[01;34m ~ $^[[00m ps -u wking | grep script^M
+    12102 pts/7    00:00:00 ^[[01;31m^[[Kscript^[[m^[[K^M
+    12103 pts/7    00:00:00 ^[[01;31m^[[Kscript^[[m^[[K^M
+    ^[]0;wking@mjolnir:~^G^[[01;32mwking@mjolnir^[[01;34m ~ $^[[00m pstr^G^M
+    pstree   pstruct  ^M
+    ^[[01;32mwking@mjolnir^[[01;34m ~ $^[[00m pstr^M
+    pstree   pstruct  ^M
+    ^[[01;32mwking@mjolnir^[[01;34m ~ $^[[00m pstree 12102^M
+    scriptM-bM-^TM-^@M-bM-^TM-^@M-bM-^TM-^@scriptM-bM-^TM-^@M-bM-^TM-^@M-bM-^TM-^@bashM-bM-^TM-^@M-bM-^TM-^@M-bM-^TM-^@pstree^M
+    ^[]0;wking@mjolnir:~^G^[[01;32mwking@mjolnir^[[01;34m ~ $^[[00m exit^M
+    exit^M
+
+    Script done on Mon 10 Dec 2012 08:07:51 AM EST
+
+You can also record timing information in a separate file (this
+approach was developed by Joey Hess and posted in [Debian bug
+68556][68556]):
+
+    $ script --timing=/tmp/timing /tmp/script
+    Script started, file is /tmp/script
+    $ echo hello
+    hello
+    $ exit
+    exit
+    Script done, file is /tmp/script
+
+The timing file has a “delay in seconds” column and a “number of
+characters to send column”:
+
+    $ cat /tmp/timing
+    0.671478 67
+    0.159100 1
+    0.941919 1
+    0.149764 1
+
+You can play back a script with timing information:
+
+    $ scriptreplay -t /tmp/timing -s /tmp/script
+    …playback…
+
+You can also play it back with altered timing (e.g. in slow motion):
+
+    $ scriptreplay -t /tmp/timing -s /tmp/script -d 0.5
+    …half-speed playback playback…
+
+This even works reasonably well with curses applications (`emacs`,
+`vi`, …), but information such as window size is not recorded or
+replayed.  From util-linux's `scriptreplay(1)`:
+
+> Since the same information is simply being displayed, scriptreplay
+> is only guaranteed to work properly if run on the same type of
+> terminal the typescript was recorded on.  Otherwise, any escape
+> characters in the typescript may be interpreted differently by the
+> terminal to which scriptreplay is sending its output.
+
+This means that if you want interoperable replay, you'll want to do
+something like
+
+    $ reset
+    $ echo "$TERM $LINES $COLUMNS"
+    xterm 24 80
+
+early on so folks know how to setup their replay environment.  If
+you're using some wonky `$TERM`, you may even want to post your
+terminfo:
+
+    $ infocmp
+    xterm|xterm terminal emulator (X Window System),
+            am, bce, km, mc5i, mir, msgr, npc, xenl,
+            colors#8, cols#80, it#8, lines#24, pairs#64,
+            acsc=``aaffggiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz{{||}}~~,
+    …
+
+The user can compare with their current terminal:
+
+    $ infocmp xterm linux
+    comparing xterm to linux.
+        comparing booleans.
+            ccc: F:T.
+            eo: F:T.
+            …
+        comparing numbers.
+            cols: 80, NULL.
+            lines: 24, NULL.
+            ncv: NULL, 18.
+        …
+
+It would be nice if there was an `iconv`-style converter to translate
+between terminal operation encodings, but I haven't found one yet.
+[[Screen]] may do something like this internally, but I do sometimes
+run into terminfo-related problems when using `screen`, so perhaps it
+does not.
+
+[68556]: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=68556