Why does the equal to operator not work if it is not surrounded by spaces?
bash, scripting, shell, syntax
Solution
`test` (or `[ expr ]`) is a builtin function. Like all functions in bash, you pass its arguments as whitespace separated words.
As the man page for bash builtins states: "Each operator and operand must be a separate argument."
It's just the way bash and most other Unix shells work.
Variable assignment is different.
In bash a variable assignment has the syntax: `name=[value]`. You cannot put unquoted spaces around the `=` because bash would not interpret this as the assignment you intend. bash treats most lists of words as a command with parameters.
E.g.
# call the command or function 'abc' with '=def' as argument
abc =def
# call 'def' with the variable 'abc' set to the empty string
abc= def
# call 'ghi' with 'abc' set to 'def'
abc=def ghi
# set 'abc' to 'def ghi'
abc="def ghi"
Problem
I tried the following script: ``` #!/bin/bash var1="Test 1" var2="Test 2" if [ "$var1"="$var2" ] then echo "Equal" else echo "Not equal" fi ``` It gave me `Equal`. Although it should have printed `Not equal` Only when I inserted space around `=` it worked as intended: ``` if [ "$var1" = "$var2" ] ``` and printed `Not equal` Why is it so? Why is `"$var1"="$var2"` not same as `"$var1" = "$var2"`? Moreover, when I wrote `if [ "$var1"= "$var2" ]`, it gave ``` line 4: [: Test 1=: unary operator expected ``` What does it mean? How come it's expecting a unary operator?