Syntax error using =~ operator in bash

Question

I'm very new to bash and I'm trying to extract a portion of a string based on a pattern, but when I execute my code I'm seeing errors.

Sample code:

#!/bin/sh

STRING="LAX-8912_Words_Are_Here";

if [[ $STRING =~ LAX-(\d)+ ]]; then
    echo "${BASH_REMATCH[1]}"
fi

So from the code above, I'm wanting to extract the "LAX-8912" portion of the string. Basically the string will be LAX- and then a series of numbers, could be any length. When the code is exectued however, I'm getting this message:

Syntax error: "(" unexpected (expecting "then")

I've also tried storing the regex in a variable like this:

#!/bin/sh

STRING="LAX-8912_Words_Are_Here";
REX="LAX-(\d)+";

if [[ $STRING =~ $REX ]]; then
    echo "${BASH_REMATCH[1]}"
fi

But then I get this error:

 [[: not found

My bash version is 4.2.25 so I'm guessing it's not a version issue, but I'm at a bit of a loss as to what's going.

that other guy · Accepted Answer · 2018-05-17 18:42:33Z

4

Since your script starts with:

#!/bin/sh

it will run the system shell, which may be a completely different shell like dash, or at best bash in compatibility mode. You should use:

#!/bin/bash

to use bash with all its features.

Similarly, if run with sh file you override the shebang and force the script to run with the system shell. Use ./file so that the script can run with its declared shebang.

edited May 17, 2018 at 18:42

that other guy

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answered Aug 23, 2014 at 5:17

Barmar

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1 Comment

MrGS Over a year ago

Oh man, how embarrassing, thank you very much for that. My regex appears to be wrong but at least now I can see the output. Thanks again.

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