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 will automatically point out this and other basic issues. — that other guy
– that other guy, Commented Nov 1, 2013 at 21:09
Another pointer: you only need a statement-terminating ; if you're putting multiple statements on a single line. — mklement0
– mklement0, Commented Nov 2, 2013 at 2:46
You need spaces between [[ and $variable and $blanko and ]] — Marcello Romani
– Marcello Romani, Commented Jan 20, 2019 at 11:02
Other question is about use of [ which is an external utility in Unix but this is different problem — anubhava
– anubhava, Commented Aug 3, 2022 at 8:16
Double check that you don't have a non breaking space instead of a regular space. I often typo a nbsp instead of a space and cause this to fail in a hard-to-understand/debug way. — odinho - Velmont
– odinho - Velmont, Commented Jun 21, 2023 at 9:20

anubhava · Accepted Answer · 2013-11-01 18:55:05Z

246

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 1, 2013 at 18:55

anubhava

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11 Comments

mklement0 Over a year ago

Note, however, that there's no need to double-quote the variable references (even if the values have embedded spaces).

anubhava Over a year ago

@mklement0: Just for good practice I always quote them, may not be always needed.

mklement0 Over a year ago

@EpsilonAlpha: English has the same saying: "[I] cannot see the forest for the trees".

quantum231 Over a year ago

but why do we need spaces in the first place like this?

anubhava Over a year ago

Because bash interprets that as a command in the absence of right syntax

|

codeforester · Accepted Answer · 2018-11-04 12:50:02Z

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

ankit · Accepted Answer · 2019-07-26 04:37:48Z

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, 2019 at 4:37

ankit

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Comments

Danny · Accepted Answer · 2020-05-12 02:02:48Z

-1

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, 2020 at 2:02

Danny

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