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--- action:Execute_a_Shell_Script [2019/05/03 13:13]
JMichaelTX ADD example of Bash quoting
+++ action:Execute_a_Shell_Script [2019/07/01 02:46]
peternlewis [Execute a Shell Script]
@@ Line 1: / Line 1: @@
-{{:action:shell-script-icon.png?nolink|}}
 ====== Execute a Shell Script ======
@@ Line 9: / Line 8: @@
 {{:action:execute-shell-script.png?nolink&693|}}
+If the script fails, the action will fail (v9.0+), potentially aborting the macro.
 ==== Using Keyboard Maestro Variables ====
@@ Line 35: / Line 36: @@
 See the [[#Forum|Forum]] section below for more Python examples.
----
 Note that you can only read these environment variables.  You cannot write to them (or more accurately, you can write to them but that will not change the Keyboard Maestro variables that they were created from).
@@ Line 73: / Line 72: @@
   * [[https://forum.keyboardmaestro.com/t/png-metadata-comment/6375/29| How To Quote Paths by @ccstone]].
   * [[https://forum.keyboardmaestro.com/t/trouble-expanding-variable-in-shell-script/13664/2?u=jmichaeltx | Trouble Expanding Variable in Shell Script by @PeterNLewis]]
----
 ==== UTF-8 and Non-ASCII Characters ====
 If you are dealing with non-ASCII characters, you probably want to set the `LC_ALL` environment variable to UTF8, which you can do by setting the Keyboard Maestro variable `ENV_LC_ALL` to “en_US.UTF-8”.
+By default (v9.0+), if you have not set these environment variables they will be set to UTF-8 for you.
 ==== Action Gear ====
-The Action (gear) menu includes the following options:
+The action (gear) ⚙ menu includes the following options:
 * Trim Results — removes white space from the start and end of the scripts results.
@@ Line 111: / Line 110: @@
 ===== Quoting Strings =====
-Proper quoting of strings in a Shell Script is often a challenge.
+Proper quoting of strings in a Shell Script is often a challenge.  In order to understand it, you have to understand what happens at each level of the processing.
+Thankfully, in an Execute Script action, Keyboard Maestro itself does not do any processing, so that is one less place for confusion.
+With shell commands, the important thing to understand is that, with only a few exceptional programs, it is not the command that does the processing, it is the shell (bash usually, although there are many shells).
+So for example with Keyboard Maestro variable set to `"Selection Style" -int 0` and en Execute Shell Script command of:
+```bash
+defaults write /Users/me/Library/Application\ Support/Witch/Settings $KMVAR_witchPref
+```
+It is the *bash* tool that sees the string and it processes it in to an array of strings which it passes to the *defaults* tool.  This is important - the defaults command receives not a single string, but an array of strings, in this case the array will be:
+* `defaults`
+* `write`
+*  `/Users/me/Library/Application Support/Witch/Settings`
+* `"Selection`
+* `Style"`
+* `-int`
+* `0`
+It is bash that has processed the variable substitution for $KMVAR_witchPref, split the line in to seven parts, processed the backslash in "Application\ Support" and then executed the defaults tool with the seven parts as arguments (the command itself is the 0th argument, normally mostly ignored by tools).
+So the problem is that the word-breaking, variable substitution, de-quoting and de-backslash is all happening at as the line is processed by bash, after which you are left with quotes from within variable substitution, but they no longer have any meaning, they are just characters.
+So variables that are meant to be a single parameter should be surrounded by double quotes in the line, but not contain quotes in the variable, and generally you do not want to pass multiple parameters within a single parameter.  So instead, perhaps set one variable to the setting name, and one variable to the type and one variable to the value, and then use a command like this:
+```bash
+defaults write "/Users/me/Library/Application Support/Witch/Settings" "$KMVAR_Setting" -"$KMVAR_Type" "$KMVAR_Value"
+```
+Now a further complication happens when you want to sent a string containing double quotes and variables to a parameter.  For example, perhaps you want a command like this:
+```bash
+emacsclient -e '(w3m-browse-url "$KMVAR_SafariURL")'
+```
+This will not work because bash only expands variables within double-quoted strings.  Within single quoted strings, they remain as the text `$KMVAR_SafariURL` (unchanged).  And so emactsclient will receive the array:
+* `emacsclient`
+* `-e`
+* `(w3m-browse-url "$KMVAR_SafariURL")`
+But it will not expand the variable (that is the shell’s job).
+To work around this you need to use either all double quotes (and backslash any double quotes within them) such as:
+```bash
+emacsclient -e "(w3m-browse-url \"$KMVAR_SafariURL\")"
+```
+or use a combination of strings, some double quoted and some single quoted:
+```bash
+emacsclient -e '(w3m-browse-url "'"$KMVAR_SafariURL"'")'
+```
+Note that that parameter is now made up of three stings combined into one parameter:
-For a discussion on how to quote a string, see this [[https://forum.keyboardmaestro.com/t/having-trouble-with-quotes-and-shell-variables/6236/9 | Keyboard Maestro Forum post by @PeterNLewis]].
+* `(w3m-browse-url "` - single quoted string
+* the value of $KMVAR_SafariURL - double quoted string
+* `")` - single quoted string

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