Shell from zero: a variable holds text

The shell stores text. item=latte puts the characters latte in item. echo prints them. There is no int until you ask for arithmetic, and that is a later lesson. A price you type is still text until then.

The value is text, and the spaces matter#

item=latte is a single word. The shell treats it as an assignment because there is no space around =. item = latte is a command named item, and the shell looks for a program by that name. The stored value is the characters of the drink, not a string object and not an int. "$item" expands to that text as one word. An unset name expands to empty unless set -u is on, in which case the expansion is an error. A child process does not see the variable unless you export it. echo is a builtin, so it sees it anyway.

1. itemtextlatte

item=latte
echo "$item"

latte

The equals sign is the assignment#

item=latte is one word to the shell. No spaces. item = latte is a command named item, which you almost certainly do not have, and the shell reports that the command was not found. The spaces changed the meaning from assignment to a program launch.

echo "$item" prints the drink. The quotes matter more in the next lesson. They are already here so the habit is in place. Without a previous assignment, $item is empty and echo prints a blank line. An unset variable is not an error unless you turned that option on.

Export when a child program must see it#

item=latte is visible to the rest of this script and to the next lines you type in this shell. A program you start does not see it unless you export item. echo is a builtin and sees it either way. The next lesson shows why the quotes around the expansion are doing work, using a drink name that contains a space.