add stop_logging_output function and test

README.md

@@ -1040,23 +1040,37 @@ printf '' >file
 ```sh
 log_all_output() {
     # Usage: log_all_output log_filename
+	exec 6>&1         # save stdout
+	exec 7>&2         # save stderr
     exec &>"$1"
 }
+
+stop_logging_output() {
+	exec 1>&6 6>&-   # Restore stdout
+	exec 2>&7 7>&-   # Restore stderr
+}
 ```
 
 **Example Usage:**
 
 ```shell
 # These are *not* logged.
-printf 'This is a message.\n'
-printf 'This is an error message.\n' >&2
+printf 'This is a normal message.\n'
+printf 'This is a normal error message.\n' >&2
 
 # All script output will go to 'myoutput.log'.
 log_all_output myoutput.log
 
 # These are now logged.
-printf 'This is a message.\n'
-printf 'This is an error message.\n' >&2
+printf 'This is a logged message.\n'
+printf 'This is a logged  error message.\n' >&2
+
+# Return to normal.
+stop_logging_output
+
+# These are not logged.
+printf 'This is a normal message.\n'
+printf 'This is a normal error message.\n' >&2
 ```
 
 ## Extract lines between two markers

manuscript/chapter4.txt

@@ -173,23 +173,37 @@ printf '' >file
 ```sh
 log_all_output() {
     # Usage: log_all_output log_filename
+	exec 6>&1         # save stdout
+	exec 7>&2         # save stderr
     exec &>"$1"
 }
+
+stop_logging_output() {
+	exec 1>&6 6>&-   # Restore stdout
+	exec 2>&7 7>&-   # Restore stderr
+}
 ```
 
 **Example Usage:**
 
 ```shell
 # These are *not* logged.
-printf 'This is a message.\n'
-printf 'This is an error message.\n' >&2
+printf 'This is a normal message.\n'
+printf 'This is a normal error message.\n' >&2
 
 # All script output will go to 'myoutput.log'.
 log_all_output myoutput.log
 
 # These are now logged.
-printf 'This is a message.\n'
-printf 'This is an error message.\n' >&2
+printf 'This is a logged message.\n'
+printf 'This is a logged  error message.\n' >&2
+
+# Return to normal.
+stop_logging_output
+
+# These are not logged.
+printf 'This is a normal message.\n'
+printf 'This is an normal error message.\n' >&2
 ```
 
 ## Extract lines between two markers

test.sh

@@ -210,7 +210,10 @@ test_log_all_output() {
 	log_all_output test.log
 	printf stdout
 	printf stderr >&2
-    )
+	stop_logging_output
+	printf stdout
+	printf stderr >&2
+    ) &> /dev/null
     contents="$(<test.log)"
     assert_equals "$contents" "stdoutstderr"
 }