2 files changed, 41 insertions, 0 deletions
diff --git a/deps.mk b/deps.mk
index 0a71175..d9409f1 100644
--- a/deps.mk
+++ b/deps.mk
@@ -4,6 +4,7 @@ sources.sh = \
 	src/color \
 	src/htmlesc \
 	src/ifnew \
+	src/ifok \
 	src/mandir \
 	src/minutes \
 	src/mkdtemp \
diff --git a/src/ifok b/src/ifok
new file mode 100755
index 0000000..9b75a9f
--- /dev/null
+++ b/src/ifok
@@ -0,0 +1,40 @@
+#!/bin/sh
+set -euo pipefail
+
+usage() {
+	cat <<-'EOF'
+		Usage:
+		  ifok [-o OUTFILE] COMMAND...
+	EOF
+}
+
+OUTFILE='/dev/stdout'
+while getopts 'o:' flag; do
+	case "$flag" in
+		(o)
+			OUTFILE="$OPTARG"
+			;;
+		(*)
+			usage >&2
+			exit 2
+			;;
+	esac
+done
+shift $((OPTIND - 1))
+
+
+if [ -w "$(dirname -- "$OUTFILE")" ]; then
+	TEMPFILE="$OUTFILE.$(uuid).tmp"
+else
+	TEMPFILE="$(mkstemp)"
+fi
+trap 'rm -f "$TEMPFILE"' EXIT
+
+STATUS=0
+"$@" > "$TEMPFILE" || STATUS=$?
+
+if [ "$STATUS" = 0 ]; then
+	mv "$TEMPFILE" "$OUTFILE" 2>/dev/null || cp "$TEMPFILE" "$OUTFILE"
+fi
+
+exit "$STATUS"