Command not found error in Bash variable assignment

Question

I have this script called test.sh:

#!/bin/bash STR = "Hello World" echo $STR 

when I run sh test.sh I get this:

test.sh: line 2: STR: command not found 

What am I doing wrong? I look at extremely basic/beginners bash scripting tutorials online and this is how they say to declare variables... So I'm not sure what I'm doing wrong.

I'm on Ubuntu Server 9.10. And yes, bash is located at /bin/bash.

Answer 1

You cannot have spaces around the = sign.

When you write:

STR = "foo" 

bash tries to run a command named STR with 2 arguments (the strings = and foo)

When you write:

STR =foo 

bash tries to run a command named STR with 1 argument (the string =foo)

When you write:

STR= foo 

bash tries to run the command foo with STR set to the empty string in its environment.

I'm not sure if this helps to clarify or if it is mere obfuscation, but note that:

1. the first command is exactly equivalent to: STR "=" "foo",
2. the second is the same as STR "=foo",
3. and the last is equivalent to STR="" foo.

The relevant section of the sh language spec, section 2.9.1 states:

A "simple command" is a sequence of optional variable assignments and redirections, in any sequence, optionally followed by words and redirections, terminated by a control operator.

In that context, a word is the command that bash is going to run. Any string containing = (in any position other than at the beginning of the string) which is not a redirection and in which the portion of the string before the = is a valid variable name is a variable assignment, while any string that is not a redirection or a variable assignment is a command. In STR = "foo", STR is not a variable assignment.

Answer 2

Drop the spaces around the = sign:

#!/bin/bash  STR="Hello World"  echo $STR