Improve GNU sed fallback while allowing use of -i.bak

On most Linux distributions (e.g. Ubuntu), there's no gsed command; the default "sed" is GNU sed with in-place editing capabilities. For those systems, we don't want the redirect + file move workaround applied. However, detecting the sed capabilities is error-prone and just as inefficient as the separate "mv" it would avoid. Instead, add a configuration that users can uncomment.

Add a new TODOTXT_SED_COMMAND config variable to allow (Linux and Cygwin) users who have GNU sed to skip the less efficient emulation; "make install" auto-detects sed in-place editing capability.

Merge pull request #447 from inkarkat/fix-inplace-sed

Author: inkarkat

Makefile

@@ -100,8 +100,15 @@ clean: test-pre-clean VERSION-FILE   ## remove dist directory and all release fi
 install: build installdirs   ## local package install
 	$(INSTALL_PROGRAM) $(DISTNAME)/todo.sh $(DEST_COMMAND)
 	$(INSTALL_DATA) $(DISTNAME)/todo_completion $(DEST_COMPLETION)
-	[ -e $(DEST_CONFIG) ] || \
-	    sed "s/^\(export[ \t]*TODO_DIR=\).*/\1~\/.todo/" $(DISTNAME)/todo.cfg > $(DEST_CONFIG)
+	if [ ! -e $(DEST_CONFIG) ]; then \
+	    sed 's@^\(export TODO_DIR=\).*@\1~/.todo@' $(DISTNAME)/todo.cfg > $(DEST_CONFIG); \
+	    if sed -i.bak 's@^# \(export TODOTXT_SED_COMMAND=sed\)$$@\1@' $(DEST_CONFIG) 2>/dev/null; then \
+	        rm -f $(DEST_CONFIG).bak; \
+	        echo 'This sed supports in-place editing.'; \
+	    else \
+	        echo 'Need sed in-place emulation here.'; \
+	    fi; \
+	fi
 
 .PHONY: uninstall
 uninstall:   ## uninstall package

todo.cfg

@@ -103,3 +103,13 @@ export TODO_FILE DONE_FILE REPORT_FILE
 # Set a default action for calling todo.sh without arguments.
 # Also allows for parameters for the action.
 # export TODOTXT_DEFAULT_ACTION=''
+
+## sed capabilities
+# If you have GNU sed or another sed that supports in-place editing
+# via -i[SUFFIX], uncomment this for a minuscule performance gain.
+# export TODOTXT_SED_COMMAND=sed
+
+# Uncomment this if you have add-ons that also do in-place editing
+# via sed, pass the -i.bak as the first argument like todo.sh itself,
+# and your system needs the in-place emulation.
+# export TODOTXT_SED_EXPORT_FOR_ADDONS=1

todo.sh

@@ -27,6 +27,25 @@ export TODO_SH TODO_FULL_SH
 
 oneline_usage="$TODO_SH [-fhpantvV] [-d todo_config] action [task_number] [task_description]"
 
+# Assumption: The in-place argument is the first
+# Assumption: Only a single file is processed with sed
+sed() {
+    if [ -n "$TODOTXT_SED_COMMAND" ]; then
+        command "$TODOTXT_SED_COMMAND" "$@"
+    elif command -v gsed &>/dev/null; then
+        gsed "$@"
+    elif [ "$1" = '-i.bak' ]; then
+        shift
+        filepath=${!#}
+        filepath_temp=${TMPDIR-/tmp}/todo.sh-sed.$RANDOM.$$
+        command sed "$@" > "$filepath_temp" && mv "$filepath_temp" "$filepath"
+    else
+        command sed "$@"
+    fi
+}
+[ "$TODOTXT_SED_EXPORT_FOR_ADDONS" = 1 ] \
+    && export -f sed
+
 usage()
 {
     cat <<-EndUsage