add alternative to command substitution for func return

Faster space trim. Safe args. Capturing STDERR

faster space trim. Safe args. Capturing Stderr

nohup not required

double fork makes PID=1 the parent and thus automatically removed it from the current session group - and by this will not receive a SIGHUP on exit (which is what we want. Nohup is redundant in this case).

Update README.md

Update README.md

README.md

@@ -161,6 +161,7 @@ See something incorrectly described, buggy or outright wrong? Open an issue or s
  * [Bypass shell aliases](#bypass-shell-aliases)
  * [Bypass shell functions](#bypass-shell-functions)
  * [Run a command in the background](#run-a-command-in-the-background)
+ * [Capture function return without command substitution](#capture-the-return-value-of-a-function-without-command-substitution)
 * [AFTERWORD](#afterword)
 
 <!-- vim-markdown-toc -->
@@ -198,6 +199,16 @@ trim_string() {
 }
 ```
 
+```sh
+trim_string_fast() {
+ local -
+ set -f
+ echo $1
+}
+```
+
+The `local -` makes `$-` local so that `set -f` is only effective within this function.
+
 **Example Usage:**
 
 ```shell
@@ -222,10 +233,10 @@ without leading/trailing white-space and with truncated spaces.
 # shellcheck disable=SC2086,SC2048
 trim_all() {
  # Usage: trim_all " example string "
+ local -
  set -f
  set -- $*
  printf '%s\n' "$*"
- set +f
 }
 ```
 
@@ -1892,9 +1903,10 @@ f()for i in "$@"; do echo "$i"; done
 
 ```shell
 # One line
-# Note: The 3rd statement may run when the 1st is true
+# Note: The 3rd statement may run when the 1st is true and 2nd false
 [[ $var == hello ]] && echo hi || echo bye
-[[ $var == hello ]] && { echo hi; echo there; } || echo bye
+# Note: The 3rd statement wont run when the 1st is true and 2nd false
+[[ $var == hello ]] && { echo hi; echo there; :; } || echo bye
 
 # Multi line (no else, single statement)
 # Note: The exit status may not be the same as with an if statement
@@ -2163,12 +2175,77 @@ This will run the given command and keep it running, even after the terminal or
 
 ```sh
 bkr() {
- (nohup "$@" &>/dev/null &)
+ ("$@" &>/dev/null &)
 }
 
 bkr ./some_script.sh # some_script.sh is now running in the background
 ```
 
+## Capture the return value of a function without command substitution
+
+**CAVEAT:** Requires `bash` 4+
+
+This uses local namerefs to avoid using `var=$(some_func)` style command substitution for function output capture.
+
+```sh
+to_upper() {
+ local -n ptr=${1}
+
+ ptr=${ptr^^}
+}
+
+foo="bar"
+to_upper foo
+printf "%s\n" "${foo}" # BAR
+```
+
+## Making a string safe for passing as argument to another command
+
+This is useful when executing a script on a remote system without copying the script (and when the remote shell is not Bash)
+
+```sh
+mk_safe_arg() {
+ # Escape all single-' with '"'"'
+ echo "${1//\'/\'\"\'\"\'}"
+}
+
+# A bash script for testing
+cat >s.sh<<-'__EOF__'
+#! /usr/bin/env bash
+echo "Hello single-' and double-\" and '$USER' on '$HOSTNAME'"
+__EOF__
+# Load the script into the variable s
+s="$(mk_safe_arg "$(<s.sh)")"
+
+# Execute the script remotely without copying the script
+ssh user@host "bash -c '$s'"
+
+# Execute locally (for testing)
+sh -c "bash -c '$s'"
+```
+
+## Capturing STDERR without capturing STDOUT.
+
+The STDOUT passes through and STDERR is stored in `err`.
+```sh
+{ err="$( { echo 1>&2 "Hello-STDERR"; exit 123; } 2>&1 1>&3 3>&- )"; } 3>&1
+echo "ret=$?, err=$err"
+# ret=123, err=Hello-STDERR
+```
+
+The inner `{..}` writes to STDERR and exits with error code 123. The STDERR from the inner `{..}` is redirected to STDOUT with `2>&1`. The normal STDOUT is redirected to the newly created File Descriptor '3' with `1>&3 3>&-`. The outter `{..}` redirects File Descriptor '3' back to STDOUT with `3>&1`.
+
+The variable `err` then contains the STDERR of the inner `{..}`.
+
+## Block coomments
+
+```sh
+:<<-'###COMMENT-BLOCK'
+This is a block comment in bash
+Test $HOME $(id) `id` {} (:;)
+###COMMENT-BLOCK
+```
+
 <!-- CHAPTER END -->
 
 # AFTERWORD

manuscript/chapter19.txt

@@ -219,11 +219,27 @@ This will run the given command and keep it running, even after the terminal or
 bkr() {
  (nohup "$@" &>/dev/null &)
 }
-```
 
-```shell
 bkr ./some_script.sh # some_script.sh is now running in the background
 ```
 
+## Capture the return value of a function without command substitution
+
+**CAVEAT:** Requires `bash` 4+
+
+This uses local namerefs to avoid using `var=$(some_func)` style command substitution for function output capture.
+
+```sh
+to_upper() {
+ local -n ptr=${1}
+
+ ptr=${ptr^^}
+}
+
+foo="bar"
+to_upper foo
+printf "%s\n" "${foo}" # BAR
+```
+
 <!-- CHAPTER END -->