Why equal to operator does not work if it is not surrounded by space?

by

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"

More Related Contents:

  1. Why equal to operator does not work if it is surrounded by space?
  2. Test for non-zero length string in Bash: [ -n “$var” ] or [ “$var” ]
  3. How to concatenate string variables in Bash
  4. How do I iterate over a range of numbers defined by variables in Bash?
  5. Difference between single and double quotes in Bash
  6. Command not found error in Bash variable assignment
  7. How do I split a string on a delimiter in Bash?
  8. Correct Bash and shell script variable capitalization
  9. When do we need curly braces around shell variables?
  10. How to urlencode data for curl command?
  11. What is the purpose of “&&” in a shell command?
  12. sudo echo “something” >> /etc/privilegedFile doesn’t work [duplicate]
  13. How can I declare and use Boolean variables in a shell script?
  14. How can I suppress all output from a command using Bash?
  15. Random number from a range in a Bash Script
  16. How to get a password from a shell script without echoing
  17. How to get the part of a file after the first line that matches a regular expression
  18. What is the difference between ${var}, “$var”, and “${var}” in the Bash shell?
  19. Copy folder recursively, excluding some folders
  20. Passing arguments by reference
  21. Get just the filename from a path in a Bash script [duplicate]
  22. What does “plus colon” (“+:”) mean in shell script expressions?
  23. How to resolve symbolic links in a shell script
  24. Extract version number from a string
  25. How to tell if a string is not defined in a Bash shell script
  26. Is there a way to avoid positional arguments in bash?
  27. What does `kill -0 $pid` in a shell script do?
  28. How to append output to the end of a text file
  29. What expands to all files in current directory recursively?
  30. In bash, is there an equivalent of die “error msg”

Leave a Comment