Cache --quiet option for bc(1) in flag file

As done for grep(1) and ls(1); ed(1) is next

2 files changed, 33 insertions, 4 deletions

diff --git a/sh/profile.d/bc.sh b/sh/profile.d/bc.sh
new file mode 100644
index 00000000..16200b33
--- /dev/null
+++ b/sh/profile.d/bc.sh
@@ -0,0 +1,22 @@
+# Test that we have metadata about what options this system's bc(1) supports,
+# and try to create it if not
+(
+    # Create a directory to hold metadata about bc
+    bcd=$HOME/.cache/bc
+    if ! [ -d "$bcd" ] ; then
+        mkdir -p -- "$bcd" || exit
+    fi
+
+    # Write bc(1)'s --help output to a file, even if it's empty
+    if ! [ -f "$bcd"/help ] ; then
+        bc --help </dev/null >"$bcd"/help 2>/dev/null || exit
+
+        # Iterate through some useful options and create files to show they're
+        # available
+        set -- quiet
+        for opt ; do
+            grep -q -- --"$opt" "$bcd"/help || continue
+            touch -- "$bcd"/"$opt" || exit
+        done
+    fi
+)
diff --git a/sh/shrc.d/bc.sh b/sh/shrc.d/bc.sh
index 643678ac..41331ff9 100644
--- a/sh/shrc.d/bc.sh
+++ b/sh/shrc.d/bc.sh
@@ -1,7 +1,14 @@
-# This function is only applicable if bc(1) has the non-POSIX -q option
-command bc -q </dev/null >&0 2>&0 || return
+# Our ~/.profile should already have made a directory with the supported
+# options for us; if not, we won't be wrapping bc(1) with a function at all
+[ -d "$HOME"/.cache/bc ] || return
 
-# Don't print the bc(1) welcome message
+# Define function proper
 bc() {
-    command bc -q "$@"
+
+    # Add --quiet to stop the annoying welcome banner
+    [ -e "$HOME"/.cache/bc/quiet ] &&
+        set -- --quiet "$@"
+
+    # Run bc(1) with the concluded arguments
+    command bc "$@"
 }