Macos Bash Prompt For Input With Default

Bash itself can only work with integers. Read Input With a Default Value The user may edit, or completely remove the default value at the prompt and type something entirely different. Still, if they just hit, that default value is used.

Macos Bash Script
Macos Bash Prompt For Input With Default Key

@Jonathan Leffler Unfortunately, not really what the OP asked for, at least not on my bash version 4.x $ bash -version GNU bash, version 4.3.33(0)-release a) 'I would like to be able to provide a default value that the user can change.'
Bash PS1 prompt variable. PS1 is a primary prompt variable. Currently it holds u@ h: w $ special bash characters. This is the default structure of the bash prompt on many Linux systems and is displayed every time you log in using a terminal. Please see the following section 'Bash prompt special characters' for explanation of u, h, w.

To use a keyboard shortcut, press and hold one or more modifier keys and then press the last key of the shortcut. For example, to use Command-C (copy), press and hold the Command key, then the C key, then release both keys. Mac menus and keyboards often use symbols for certain keys, including modifier keys:

On keyboards made for Windows PCs, use the Alt key instead of Option, and the Windows logo key instead of Command.

Some keys on some Apple keyboards have special symbols and functions, such as for display brightness , keyboard brightness , Mission Control, and more. If these functions aren't available on your keyboard, you might be able to reproduce some of them by creating your own keyboard shortcuts. To use these keys as F1, F2, F3, or other standard function keys, combine them with the Fn key.

Cut, copy, paste, and other common shortcuts

Command-X: Cut the selected item and copy it to the Clipboard.
Command-C: Copy the selected item to the Clipboard. This also works for files in the Finder.
Command-V: Paste the contents of the Clipboard into the current document or app. This also works for files in the Finder.
Command-Z: Undo the previous command. You can then press Shift-Command-Z to Redo, reversing the undo command. In some apps, you can undo and redo multiple commands.
Command-A: Select All items.
Command-F: Find items in a document or open a Find window.
Command-G: Find Again: Find the next occurrence of the item previously found. To find the previous occurrence, press Shift-Command-G.
Command-H: Hide the windows of the front app. To view the front app but hide all other apps, press Option-Command-H.
Command-M: Minimize the front window to the Dock. To minimize all windows of the front app, press Option-Command-M.
Command-O: Open the selected item, or open a dialog to select a file to open.
Command-P: Print the current document.
Command-S: Save the current document.
Command-T: Open a new tab.
Command-W: Close the front window. To close all windows of the app, press Option-Command-W.
Option-Command-Esc: Force quit an app.
Command–Space bar: Show or hide the Spotlight search field. To perform a Spotlight search from a Finder window, press Command–Option–Space bar. (If you use multiple input sources to type in different languages, these shortcuts change input sources instead of showing Spotlight. Learn how to change a conflicting keyboard shortcut.)
Control–Command–Space bar: Show the Character Viewer, from which you can choose emoji and other symbols.
Control-Command-F: Use the app in full screen, if supported by the app.
Space bar: Use Quick Look to preview the selected item.
Command-Tab: Switch to the next most recently used app among your open apps.
Shift-Command-5: In macOS Mojave or later, take a screenshot or make a screen recording. Or use Shift-Command-3 or Shift-Command-4 for screenshots. Learn more about screenshots.
Shift-Command-N: Create a new folder in the Finder.
Command-Comma (,): Open preferences for the front app.

Sleep, log out, and shut down shortcuts

You might need to press and hold some of these shortcuts for slightly longer than other shortcuts. This helps you to avoid using them unintentionally.

Power button: Press to turn on your Mac or wake it from sleep. Press and hold for 1.5 seconds to put your Mac to sleep.* Continue holding to force your Mac to turn off.
Option–Command–Power button* or Option–Command–Media Eject : Put your Mac to sleep.
Control–Shift–Power button* or Control–Shift–Media Eject : Put your displays to sleep.
Control–Power button* or Control–Media Eject : Display a dialog asking whether you want to restart, sleep, or shut down.
Control–Command–Power button:* Force your Mac to restart, without prompting to save any open and unsaved documents.
Control–Command–Media Eject : Quit all apps, then restart your Mac. If any open documents have unsaved changes, you will be asked whether you want to save them.
Control–Option–Command–Power button* or Control–Option–Command–Media Eject : Quit all apps, then shut down your Mac. If any open documents have unsaved changes, you will be asked whether you want to save them.
Control-Command-Q: Immediately lock your screen.
Shift-Command-Q: Log out of your macOS user account. You will be asked to confirm. To log out immediately without confirming, press Option-Shift-Command-Q.

* Does not apply to the Touch ID sensor.

Finder and system shortcuts

Command-D: Duplicate the selected files.
Command-E: Eject the selected disk or volume.
Command-F: Start a Spotlight search in the Finder window.
Command-I: Show the Get Info window for a selected file.
Command-R: (1) When an alias is selected in the Finder: show the original file for the selected alias. (2) In some apps, such as Calendar or Safari, refresh or reload the page. (3) In Software Update preferences, check for software updates again.
Shift-Command-C: Open the Computer window.
Shift-Command-D: Open the desktop folder.
Shift-Command-F: Open the Recents window, showing all of the files you viewed or changed recently.
Shift-Command-G: Open a Go to Folder window.
Shift-Command-H: Open the Home folder of the current macOS user account.
Shift-Command-I: Open iCloud Drive.
Shift-Command-K: Open the Network window.
Option-Command-L: Open the Downloads folder.
Shift-Command-N: Create a new folder.
Shift-Command-O: Open the Documents folder.
Shift-Command-P: Show or hide the Preview pane in Finder windows.
Shift-Command-R: Open the AirDrop window.
Shift-Command-T: Show or hide the tab bar in Finder windows.
Control-Shift-Command-T: Add selected Finder item to the Dock (OS X Mavericks or later)
Shift-Command-U: Open the Utilities folder.
Option-Command-D: Show or hide the Dock.
Control-Command-T: Add the selected item to the sidebar (OS X Mavericks or later).
Option-Command-P: Hide or show the path bar in Finder windows.
Option-Command-S: Hide or show the Sidebar in Finder windows.
Command–Slash (/): Hide or show the status bar in Finder windows.
Command-J: Show View Options.
Command-K: Open the Connect to Server window.
Control-Command-A: Make an alias of the selected item.
Command-N: Open a new Finder window.
Option-Command-N: Create a new Smart Folder.
Command-T: Show or hide the tab bar when a single tab is open in the current Finder window.
Option-Command-T: Show or hide the toolbar when a single tab is open in the current Finder window.
Option-Command-V: Move the files in the Clipboard from their original location to the current location.
Command-Y: Use Quick Look to preview the selected files.
Option-Command-Y: View a Quick Look slideshow of the selected files.
Command-1: View the items in the Finder window as icons.
Command-2: View the items in a Finder window as a list.
Command-3: View the items in a Finder window in columns.
Command-4: View the items in a Finder window in a gallery.
Command–Left Bracket ([): Go to the previous folder.
Command–Right Bracket (]): Go to the next folder.
Command–Up Arrow: Open the folder that contains the current folder.
Command–Control–Up Arrow: Open the folder that contains the current folder in a new window.
Command–Down Arrow: Open the selected item.
Right Arrow: Open the selected folder. This works only when in list view.
Left Arrow: Close the selected folder. This works only when in list view.
Command-Delete: Move the selected item to the Trash.
Shift-Command-Delete: Empty the Trash.
Option-Shift-Command-Delete: Empty the Trash without confirmation dialog.
Command–Brightness Down: Turn video mirroring on or off when your Mac is connected to more than one display.
Option–Brightness Up: Open Displays preferences. This works with either Brightness key.
Control–Brightness Up or Control–Brightness Down: Change the brightness of your external display, if supported by your display.
Option–Shift–Brightness Up or Option–Shift–Brightness Down: Adjust the display brightness in smaller steps. Add the Control key to this shortcut to make the adjustment on your external display, if supported by your display.
Option–Mission Control: Open Mission Control preferences.
Command–Mission Control: Show the desktop.
Control–Down Arrow: Show all windows of the front app.
Option–Volume Up: Open Sound preferences. This works with any of the volume keys.
Option–Shift–Volume Up or Option–Shift–Volume Down: Adjust the sound volume in smaller steps.
Option–Keyboard Brightness Up: Open Keyboard preferences. This works with either Keyboard Brightness key.
Option–Shift–Keyboard Brightness Up or Option–Shift–Keyboard Brightness Down: Adjust the keyboard brightness in smaller steps.
Option key while double-clicking: Open the item in a separate window, then close the original window.
Command key while double-clicking: Open a folder in a separate tab or window.
Command key while dragging to another volume: Move the dragged item to the other volume, instead of copying it.
Option key while dragging: Copy the dragged item. The pointer changes while you drag the item.
Option-Command while dragging: Make an alias of the dragged item. The pointer changes while you drag the item.
Option-click a disclosure triangle: Open all folders within the selected folder. This works only when in list view.
Command-click a window title: See the folders that contain the current folder.
Learn how to use Command or Shift to select multiple items in the Finder.
Click the Go menu in the Finder menu bar to see shortcuts for opening many commonly used folders, such as Applications, Documents, Downloads, Utilities, and iCloud Drive.

Document shortcuts

The behavior of these shortcuts may vary with the app you're using.

Command-B: Boldface the selected text, or turn boldfacing on or off.
Command-I: Italicize the selected text, or turn italics on or off.
Command-K: Add a web link.
Command-U: Underline the selected text, or turn underlining on or off.
Command-T: Show or hide the Fonts window.
Command-D: Select the Desktop folder from within an Open dialog or Save dialog.
Control-Command-D: Show or hide the definition of the selected word.
Shift-Command-Colon (:): Display the Spelling and Grammar window.
Command-Semicolon (;): Find misspelled words in the document.
Option-Delete: Delete the word to the left of the insertion point.
Control-H: Delete the character to the left of the insertion point. Or use Delete.
Control-D: Delete the character to the right of the insertion point. Or use Fn-Delete.
Fn-Delete: Forward delete on keyboards that don't have a Forward Delete key. Or use Control-D.
Control-K: Delete the text between the insertion point and the end of the line or paragraph.
Fn–Up Arrow: Page Up: Scroll up one page.
Fn–Down Arrow: Page Down: Scroll down one page.
Fn–Left Arrow: Home: Scroll to the beginning of a document.
Fn–Right Arrow: End: Scroll to the end of a document.
Command–Up Arrow: Move the insertion point to the beginning of the document.
Command–Down Arrow: Move the insertion point to the end of the document.
Command–Left Arrow: Move the insertion point to the beginning of the current line.
Command–Right Arrow: Move the insertion point to the end of the current line.
Option–Left Arrow: Move the insertion point to the beginning of the previous word.
Option–Right Arrow: Move the insertion point to the end of the next word.
Shift–Command–Up Arrow: Select the text between the insertion point and the beginning of the document.
Shift–Command–Down Arrow: Select the text between the insertion point and the end of the document.
Shift–Command–Left Arrow: Select the text between the insertion point and the beginning of the current line.
Shift–Command–Right Arrow: Select the text between the insertion point and the end of the current line.
Shift–Up Arrow: Extend text selection to the nearest character at the same horizontal location on the line above.
Shift–Down Arrow: Extend text selection to the nearest character at the same horizontal location on the line below.
Shift–Left Arrow: Extend text selection one character to the left.
Shift–Right Arrow: Extend text selection one character to the right.
Option–Shift–Up Arrow: Extend text selection to the beginning of the current paragraph, then to the beginning of the following paragraph if pressed again.
Option–Shift–Down Arrow: Extend text selection to the end of the current paragraph, then to the end of the following paragraph if pressed again.
Option–Shift–Left Arrow: Extend text selection to the beginning of the current word, then to the beginning of the following word if pressed again.
Option–Shift–Right Arrow: Extend text selection to the end of the current word, then to the end of the following word if pressed again.
Control-A: Move to the beginning of the line or paragraph.
Control-E: Move to the end of a line or paragraph.
Control-F: Move one character forward.
Control-B: Move one character backward.
Control-L: Center the cursor or selection in the visible area.
Control-P: Move up one line.
Control-N: Move down one line.
Control-O: Insert a new line after the insertion point.
Control-T: Swap the character behind the insertion point with the character in front of the insertion point.
Command–Left Curly Bracket ({): Left align.
Command–Right Curly Bracket (}): Right align.
Shift–Command–Vertical bar (|): Center align.
Option-Command-F: Go to the search field.
Option-Command-T: Show or hide a toolbar in the app.
Option-Command-C: Copy Style: Copy the formatting settings of the selected item to the Clipboard.
Option-Command-V: Paste Style: Apply the copied style to the selected item.
Option-Shift-Command-V: Paste and Match Style: Apply the style of the surrounding content to the item pasted within that content.
Option-Command-I: Show or hide the inspector window.
Shift-Command-P: Page setup: Display a window for selecting document settings.
Shift-Command-S: Display the Save As dialog, or duplicate the current document.
Shift–Command–Minus sign (-): Decrease the size of the selected item.
Shift–Command–Plus sign (+): Increase the size of the selected item. Command–Equal sign (=) performs the same function.
Shift–Command–Question mark (?): Open the Help menu.

Other shortcuts

For more shortcuts, check the shortcut abbreviations shown in the menus of your apps. Every app can have its own shortcuts, and shortcuts that work in one app might not work in another.

Apple Music shortcuts: Choose Help > Keyboard shortcuts from the menu bar in the Music app.
Other shortcuts: Choose Apple menu > System Preferences, click Keyboard, then click Shortcuts.

Learn more

Create your own shortcuts and resolve conflicts between shortcuts
Change the behavior of the function keys or modifier keys

One way to provide input to shell scripts (as well for programs written in other programming languges than the shell) is by providing arguments upon starting the program. That is useful and intersting. In this post, however, we will see means to provide input to a shell script that is already running. That is, the script runs, and then at some point it needs to ask the user for input so it can perform whatever actions are needed to fulfill its purpose in life!

Let’s have fun, shall we‽

Read two numbers and print the result of dividing the first by the second:

Don’t get confused here! It may look like we are passing arguments to the script, but we are not. Instead, we are justing using Shell herestrings (<<< '10 3') to provide input to the program after it is already running. It is the same as if we did something like this:

Read two numbers into the variables x and y, then sum them and store the result in the varaible result, and finally print the result to the output.

Note

We used the bc program (just for fun) to do the math so it also works with floating pointer numbers. Bash itself can only work with integers.

The user may edit, or completely remove the default value at the prompt and type something entirely different. Still, if they just hit <RET>, that default value is used.

read has a -t command line option that we can use to cause the script to continue after N seconds even if the user doesn’t hit <RET>.

But what if we do not hit <RET> and wait for the time to pass and the script to just continue execution?

When we run the script, we intentionally let the 3 seconds pass without hitting <RET>. The result is that username is not assigned any value and the printf line gives the output you see above, that is, it prints nothing for username because it is empty.

Still, there are ways to circumvent that “limitation”. We can make use of the || operator to assign a value to the variable username in case the read expressions return a false value.

Let’s study this example:

To understand how the read line works, recall that when you run a command, it returns an status value. That status value can be read through the $? special variable in bash. Zero means the command succeeded, and any other value means there was some sort of error, and it depends each program. An example:

As it can be seen, if ls succeeds in listing the file .gititnore, its status value is 0 (true). If the file does not exist, it returns 2 (one of the many possible falsy value codes for ls; check its man page).

In the line:

The || operator checks for the return value of the read command, and if it returns a non-zero value (indicating some sort of failure, i.e. no input is given), bash then proceeds to the expression username=Yoda.

Note, however, that this doesn’t work:

You may think, “Okay, if the user doesn’t hit <RET> before the three seconds, the variable username will contain the original value.” Incorrect! username will be overridden with nothingness. So, using the || approach is the way to go for something like this.

There is yet another way to provide a default value for input and have a timeout that works no matter whether the user hits <RET> or not: using Bash’s parameter expansion.

The expression username=${username:-Yoda} means, “if username has a value, just use that value, otherwise, use ‘Yoda’ instead.”

If you want to check on the command line how this type of expansion works, try this:

In the first echo line, we used a jedi variable that had not been previously set; it was empty. Since it was empty, the shell used the default value of ‘Obiwan Kenobi’ and that was the output of that first echo.

Then, we set the variable jedi to the value ‘Luke Skywalker’. When we tried the second echo command, the shell saw that jedi had a value, and printed that value instead of using the default one.

Basically, it is like this:

In this example, we prompt the user for a “Yes/No” type of question to decide if the script should do one thing or another. We also handle the case for when they type unacceptable input.

We read the user input into the answer variable and then use it in a Bash’s case statement to decide what to do based on that input.

Because our first test is [Yy]*, it means the user may type either an uppercase or lowercase “y” followed by any other character, so they may type something like “Yessss!”, and it would still match.
The reasoning explained above is the same for the pattern [Nn]*. All that matters is that the input starts with either an uppercase or a lowercase “n”.
Finally, if neither of the first two patterns match anything, we have a catch all pattern * that handles uncacceptable input.

Note

This pattern matching stuff is a subject for another (TODO) post.

Specifically for man pages, you can always open them in a browser. Do something like:

And then look in the index for the specific section you want and click the link.

read

Read the man page of the read builtin:

Or look for it in the SHELL BUILTIN COMMANDS in the bash manual. This works with the less pager:

and scroll until you see the read entry. If your pager is set to something other than less, just read its help/man pages to figure out how to search in them. To try with less even with something else set as your default pager program, you can just do this:

Macos Bash Script

bc

The man page:

Or the more verbose, informative and with examples, info page:

Macos Bash Prompt For Input With Default Key

Bash Parameter Expansion

In the man page:

Or more especifically in