[PATCH -perfbook v4] utilities/autodate.sh: Fix potential hung-up on missing tcolorbox

[Akira Yokosawa <akiyks@xxxxxxxxx>]

"kpsewhich tcolorbox.sty" can be empty if tcolorbox is not
available.

If this is the case, "grep" in `grep ProvidePackage | sed ...`
will wait forever.

Add existence check of tcolorbox early in the script and error-exit.

To prevent empty autodate.tex from left behind, modify the behavior
of the script so that it doesn't rely on the redirection in Makefile.

Fixes: b2f19231bcc5 ("utilities/autodate.sh: Make newer tcolorbox behave as before")
Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
Changes since v3:

o Fix typo of "See See" in the error message.
o Move existence check of tcolorbox to the beginning.
o Use redirection in the script, not in the Makefile

Change since v2:

o Refer to #5 in FAQ-BUILD.txt, as tcolorbox is not a font package.

Change since v1:

o Fix string comparison operator of shell script ("=").

--
 Makefile              |  2 +-
 utilities/autodate.sh | 24 ++++++++++++++++--------
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index dc6b68e0..b23a7096 100644
--- a/Makefile
+++ b/Makefile
@@ -234,7 +234,7 @@ endif
 autodate.tex: perfbook-lt.tex $(LATEXSOURCES) $(BIBSOURCES) \
     $(PDFTARGETS_OF_EPS) $(PDFTARGETS_OF_SVG) $(FCVSNIPPETS) $(FCVSNIPPETS_VIA_LTMS) \
     $(GITREFSTAGS) utilities/autodate.sh
-	sh utilities/autodate.sh >autodate.tex
+	sh utilities/autodate.sh
 
 perfbook_flat.tex: autodate.tex
 ifndef LATEXPAND
diff --git a/utilities/autodate.sh b/utilities/autodate.sh
index 7bd7cbb8..e33c254d 100644
--- a/utilities/autodate.sh
+++ b/utilities/autodate.sh
@@ -19,12 +19,21 @@
 # along with this program; if not, you can access it online at
 # http://www.gnu.org/licenses/gpl-2.0.html.
 #
-# Copyright (C) Akira Yokosawa, 2017--2020
+# Copyright (C) Akira Yokosawa, 2017--2021
 #
 # Authors: Akira Yokosawa <akiyks@xxxxxxxxx>
 
 export LC_TIME=C
 qqzbg="false"
+fn="autodate.tex"
+
+# check if we have tcolorbox
+tcolorbox_sty=`kpsewhich tcolorbox.sty`
+if [ "$tcolorbox_sty" = "" ]
+then
+	echo "Error: package 'tcolorbox' not found. See #5 in FAQ-BUILD.txt." >&2
+	exit 1
+fi
 
 # check if we are in git repository
 if ! test -e .git
@@ -90,17 +99,16 @@ then
 	release=`env printf '%s %s' '\\\\' "$release"`
 fi
 
-env printf '\\date{%s %s, %s %s %s}\n' $month $day $year "$release" $modified
-env printf '\\newcommand{\\commityear}{%s}\n' $year
-env printf '\\newcommand{\\commitid}{%s}\n' $commitid$modified
-env printf '\\IfQqzBg{}{\\setboolean{qqzbg}{%s}}\n' $qqzbg
+env printf '\\date{%s %s, %s %s %s}\n' $month $day $year "$release" $modified > $fn
+env printf '\\newcommand{\\commityear}{%s}\n' $year >> $fn
+env printf '\\newcommand{\\commitid}{%s}\n' $commitid$modified >> $fn
+env printf '\\IfQqzBg{}{\\setboolean{qqzbg}{%s}}\n' $qqzbg >> $fn
 
 # command for newer tcolorbox (4.40 or later) to have backward-compatible skips
-tcolorbox_sty=`kpsewhich tcolorbox.sty`
 tcbversion=`grep ProvidesPackage $tcolorbox_sty | sed -e 's/.*version \([0-9]\+\.[0-9]\+\).*/\1/g'`
 tcbold=4.39
-env printf '%% tcolorbox version: %s\n' $tcbversion
+env printf '%% tcolorbox version: %s\n' $tcbversion >> $fn
 if [ $(echo $tcbversion $tcbold | awk '{if ($1 > $2) print 1;}') ] ;
 then
-	env printf '\\tcbsetforeverylayer{autoparskip}\n';
+	env printf '\\tcbsetforeverylayer{autoparskip}\n' >> $fn
 fi
-- 
2.17.1