Reading Input with read

Before backup.sh packs a 4 GB folder, it would be kind to ask: are you sure? A script can pause, wait for the user to type a line, and use the answer. The tool for that is read, built into Bash.

The rule

read -r -p asks, waits, and stores the line in your variable.

• -p "text" prints a prompt and waits on the same line.
• -r keeps backslashes as typed. Without it, read treats \ as an escape and silently removes it. Use -r every time unless you have a reason not to.
• answer is where the line goes. If you give no name at all, it goes into the variable REPLY.

With several names, read splits the line on whitespace: the first word goes to the first name, the second to the second, and the last name takes everything left over. Leading and trailing spaces are trimmed.

Other useful options: -s hides what is typed (for passwords), -t 10 gives up after 10 seconds, and -n 1 returns after a single key. When the input ends (the user presses Ctrl-D, or a file runs out), read returns a failure status. The loops section uses that to read files line by line.

The shortcut

Every read is a three-beat pattern: prompt, name, check. Write the prompt the user sees, choose the variable, then check the value before trusting it, because people type Y, yes, or nothing at all. (The section on conditionals shows how to check it neatly.)

Drills

Answer fast — trust the rule.

Remember

• read -r -p "prompt " name asks, waits, and stores the line.
• Prompt, name, check: never trust the answer unchecked.
• Several names split the line; the last name takes the rest.