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bash sh shell syntax variable-assignment

Command not found error in Bash variable assignment

663

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.

5

  • 100

    I’m glad you did ask the question, you’re not the only bash noob out there!

    Aug 26, 2015 at 10:40

  • 9

    Thanks for asking that question. This is not a question to be embarrassed about. I am working late night in office & there is no Bash expert around me to answer this.

    Jan 19, 2016 at 16:49

  • 4

    These days (almost seven years later!) there’s a FOSS linter/analyzer called shellcheck that will autodetect this and other common syntax issues. It can be used online or installed offline and integrated in your editor.

    Nov 8, 2016 at 17:52

  • See also stackoverflow.com/questions/26971987/…

    – tripleee

    Oct 2, 2017 at 13:36

  • I’d recommend you to use: #!/usr/bin/env bash instead of putting directly #!/bin/bash unless you’re absolutely sure your bash is in /bin because of this answer: stackoverflow.com/a/21613044/3589567

    Feb 21, 2018 at 10:58

1157

+100

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.

9

  • 6

    If you have a variable with a name that contaings “-“, the same error happens. In that case, the solution is to remove the “-“

    – chomp

    Jun 17, 2016 at 2:27

  • 3

    [email protected] In rule 7b of section 2.10.10 of pubs.opengroup.org/onlinepubs/9699919799 “If all the characters preceding ‘=’ form a valid name (see XBD Name), the token ASSIGNMENT_WORD shall be returned.” Following the link to section 3.231 of pubs.opengroup.org/onlinepubs/9699919799, we find “In the shell command language, a word consisting solely of underscores, digits, and alphabetics from the portable character set. The first character of a name is not a digit.”. So the word FOO-BAR=qux is not a variable assignment since FOO-BAR is not a valid name.

    Jun 17, 2016 at 13:30

  • 2

    I am offering a bounty to reward this clear explanation to an always common issue for beginners (well, and also to be able to find it faster whenever I want to link it :D). Thanks for making things this easy!

    – fedorqui

    Aug 16, 2016 at 11:54

  • 1

    @fedorqui Thanks! I’m not entirely convinced that this is a clear explanation, and I often wonder if it could be made simpler.

    Aug 16, 2016 at 21:29

  • 2

    @Timo $st=$i is not a variable assignment. It expands to a string, and that string is executed as a command. It seems like you are trying to do eval $st=$i. Don’t do that.

    Nov 9, 2020 at 17:05


191

Drop the spaces around the = sign:

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

3

  • 11

    This is funny, though, as set foo = bar is a common mistake in Windows batch files as well—and there the batch language is ridiculed for it 😉

    – Joey

    Feb 15, 2010 at 18:36

  • Thanks @joey. I was stuck in writing a shell script where i was initializing variables with spaces after “=”. You saved my day

    – Lalit Rao

    Oct 2, 2015 at 13:10

  • Why bash doesn’t accept numbers in the left field? like 3=”Hello World”, it complains about command not found

    – Freedo

    Jan 19, 2018 at 16:51

9

In the interactive mode everything looks fine:

$ str="Hello World"
$ echo $str
Hello World

Obviously(!) as Johannes said, no space around =. In case there is any space around = then in the interactive mode it gives errors as

No command ‘str’ found

3

  • 3

    But note the OP was saying STR = "Hello World", so this answer does not apply here.

    – fedorqui

    Aug 16, 2016 at 12:05

  • @Arkapravo what is the meaning of the interactive mode, is it has something to do with the $ mark

    Nov 22, 2016 at 13:24

  • @KasunSiyambalapitiya by “interactive mode” he means typing those commands in the actual terminal, not into a script.

    Jan 5, 2017 at 23:59