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up vote 2 down vote favorite

I have problem with running my simple shell script, where I am using while loop to read text file and trying to check condition with matching regexp:

#!/bin/sh
regex="^sometext"


cat input.txt | 
{
  while read string
    do if [[ $string ~= $regex ]]; then
            echo "$string" | awk '{print $1}' >> output.txt
       else
            echo "$string" >> outfile.txt
       fi
    done
}

but I recieve only errors like 

[[: not found

could you please advise me?

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3 Answers 3

up vote 2 down vote accepted

Because you're using shebang for /bin/sh and [[ is only available in BASH.

Change shebang to /bin/bash

btw your script can be totally handled in simple awk and you don't need to use awk inside the while loop here.

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Thanks a lot for pointing this. So if I have no bash I can't use this condition? –  P.S. Oct 30 '13 at 17:36
1  
Yes that's correct if you don't have BASH then you can't use =~ regex operator either. –  anubhava Oct 30 '13 at 17:37
    
Thanks !! Now all clear! –  P.S. Oct 30 '13 at 17:39
    
You're welcome, if you are satisfied please mark the answer as accepted. –  anubhava Oct 30 '13 at 17:46
up vote 2 down vote

[[ expr ]] is a bash-ism; sh doesn't have it.

Use #!/bin/bash if you want to use that syntax.

That said, why use a shell script?

Awk can already do everything you're doing here - you just need to take advantage of Awk's built-in regex matching and the ability to have multiple actions per line:

Your original script can be reduced to this command:

awk '/^sometext/ {print $1; next} {print}' input.txt >> output.txt

If the pattern matches, Awk will run the first {}-block, which does a print $1 and then forces Awk to move to the next line. Otherwise, it'll continue on to the second {}-block, which just prints the line.

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1  
Just 23 seconds :) –  anubhava Oct 30 '13 at 17:35
    
@anubhava I don't generally try to race. –  Amber Oct 30 '13 at 17:46
    
Thanks for comment! I simplified my script a bit to post here. Full command after checking condition is echo "$string" | awk '{print $1}' | base64 -d | iconv -f UTF-8 -t KOI8-R >> outfile.txt –  P.S. Oct 30 '13 at 17:47
    
@Amber: Don't take it otherwise, all 3 of us answered pretty much same thing that's why I commented. –  anubhava Oct 30 '13 at 17:48
    
@P.S. You can call shell commands from awk as well. :) –  Amber Oct 30 '13 at 17:51
up vote 0 down vote

sh does not support the double bracket syntax - that's explicitly a bash-ism.

Try changing your shebang line to #!/bin/bash

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