1 files changed, 28 insertions, 19 deletions
diff --git a/examples/write_date.sh b/examples/write_date.sh
index b8e610b..d9ae3ec 100755
--- a/examples/write_date.sh
+++ b/examples/write_date.sh
@@ -20,35 +20,44 @@
 # $ ./write_date.sh -f now.out
 # $ cat now.out
 
-# source shflags
-. ../src/shflags
+# Source shFlags.
+. ../shflags
 
-# configure shflags
+# Configure shFlags.
 DEFINE_boolean 'force' false 'force overwriting' 'f'
 FLAGS_HELP="USAGE: $0 [flags] filename"
 
-
-write_date()
-{
-  date >"$1"
-}
-
-die()
-{
-  [ $# -gt 0 ] && echo "error: $@" >&2
+die() {
+  [ $# -gt 0 ] && echo "error: $@"
   flags_help
   exit 1
 }
 
-
-# parse the command-line
+# Parse the command-line.
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
 
-# check for filename
-[ $# -gt 0 ] || die 'filename missing'
+# Check for filename on command-line.
+[ $# -gt 0 ] || die 'filename missing.'
 filename=$1
 
-[ -f "${filename}" -a ${FLAGS_force} -eq ${FLAGS_FALSE} ] \
-    && die 'filename exists; not overwriting'
-write_date "${filename}"
+# Redirect STDOUT to the file ($1). This seemingly complicated method using exec
+# is used so that a potential race condition between checking for the presence
+# of the file and writing to the file is mitigated.
+if [ ${FLAGS_force} -eq ${FLAGS_FALSE} ] ; then
+  [ ! -f "${filename}" ] || die "file \"${filename}\" already exists."
+  # Set noclobber, redirect STDOUT to the file, first saving STDOUT to fd 4.
+  set -C
+  exec 4>&1 >"${filename}"  # This fails if the file exists.
+else
+  # Forcefully overwrite (clobber) the file.
+  exec 4>&1 >|"${filename}"
+fi
+
+# What time is it?
+date
+
+# Restore STDOUT from file descriptor 4, and close fd 4.
+exec 1>&4 4>&-
+
+echo "The current date was written to \"${filename}\"."