Getting "command not found" error while comparing two strings in Bash

Question

My whole Script is currently this:

#!/bin/sh   
clear;   
blanko="";   
# Dummy-Variablen
variable=Testvariable;   
if [[$variable == $blanko]];
then   
  echo "Nichts da!"   
else   
  echo $variable   
fi

and if i enter

TestSelect.sh

i get

/usr/bin/TestSelect.sh: line 6: [[Testvariable: command not found   
Testvariable

how can i fix this?

Tip for the future: [shellcheck](http://www.shellcheck.net) will automatically point out this and other basic issues. — that other guy, Nov 01 '13 at 21:09
Another pointer: you only need a statement-terminating `;` if you're putting _multiple_ statements on a single line. — mklement0, Nov 02 '13 at 02:46
You need spaces between `[[` and `$variable` and `$blanko` and `]]` — Marcello Romani, Jan 20 '19 at 11:02

score 161 · Accepted Answer · answered Nov 01 '13 at 18:55

161

This is problem:

if [[$variable == $blanko]];

Spaces are required inside square brackets, use it like this:

[[ "$variable" == "$blanko" ]] && echo "Nichts da!" || echo "$variable"

answered Nov 01 '13 at 18:55

anubhava

664,788
59
469
547

3

Big Thanks. In Germany we have a saying: "I don't see the Forest because the Trees" – EpsilonAlpha Nov 01 '13 at 18:58
Note, however, that there's no need to double-quote the variable references (even if the values have embedded spaces). – mklement0 Nov 01 '13 at 21:13
@mklement0: Just for good practice I always quote them, may not be always needed. – anubhava Nov 01 '13 at 21:16
@mklement0 original it was a testvariable cause i didn't know for sure if I correctly described an empty string, to be honest. – EpsilonAlpha Nov 01 '13 at 21:37
@anubhava: Certainly a safe approach - when what shell expansions take place is not easy to remember; when in doubt, `man bash` describes them (some digging required). – mklement0 Nov 02 '13 at 02:48
3

@EpsilonAlpha: English has the same saying: "[I] cannot see the forest for the trees". – mklement0 Nov 02 '13 at 02:50
@mklement0: Thanks, very correctly put. Quoting most of the times will be safe. – anubhava Nov 02 '13 at 04:39
but why do we need spaces in the first place like this? – quantum231 May 20 '21 at 14:50
@quantum231: That is bash syntax – anubhava May 20 '21 at 14:53
ok, but why do we get a "command not found" error in place of "syntax" error? – quantum231 May 20 '21 at 14:55
Because bash interprets that as a command in the absence of right syntax – anubhava May 20 '21 at 14:56

codeforester · Answer 2 · 2018-11-04T12:50:02.810

On a related note, spaces are required around [ ] as well:

if [ "$variable" = "$blanko" ]; then
  # more code here
fi

Note that variables do need to be enclosed in double quotes inside [ ] to prevent word splitting and globbing. Double quotes also help when either of the variables being compared is not set - shell will throw a syntax error otherwise.

Look at the following post to understand why we need spaces around [ ]:

Why should there be a space after '[' and before ']' in Bash?

Another related post that talks about other syntax elements that need spaces as well:

Why is whitespace sometimes needed around metacharacters?

Finally, this post talks about the difference between [[ ]] and [ ]:

Difference between single and double square brackets in Bash

“0: command not found” in Bash

score 0 · Answer 3 · answered Jul 26 '19 at 04:37

0

Just use #!/bin/bash on tope of script if you are using bash scripting like: if [[ $partition == "/dev/sda2" ]]; then to compare string and run script with ./scriptname.sh or bash scriptname.sh

answered Jul 26 '19 at 04:37

ankit

1,919
19
39

score 0 · Answer 4 · answered May 12 '20 at 02:02

0

If your script runs on your local with /bin/bash but not on your container with sh, then consider adding bash to your container by apk add --no-cache bash.

answered May 12 '20 at 02:02

Danny

106
2
8

Getting "command not found" error while comparing two strings in Bash

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