虽然 shell 脚本中的循环在 linux bash shell 中不起作用

Question

Am kind of newbie in writing shell scripts in linux. Its a csh script but am running it in the bash shell that why I used #!/bin/bash instead of #!/bin/csh .

  1 #!/bin/bash
  2 set i = 1
  3 echo it starts
  4 
  5 while ($i <= 5)
  6         echo i is $i
  7         @ i= $i +1
  8 end

**Note: ** The numbers are just to number the lines.

The above code gives me the output with error:

 it starts ./me.csh: line 9: syntax error: unexpected end of file

I can't figure out what is wrong even though it echos it starts and there is no line number 9 as specified in the error.

Answer 1

The shebang must be set to the shell that should interpret the script. It doesn't matter which shell you run the script from. The only thing that matters is the language the script is written in.

Your script is written in csh , and must therefore have the shebang #!/bin/csh . This is true even if you want to run it from bash. Also, you were missing a space in your at-sign-ment:

$ cat me.csh
#!/bin/csh
set i = 1
echo it starts

while ($i <= 5)
        echo i is $i
        @ i = $i + 1
end

Output:

$ ./me.csh
it starts
i is 1
i is 2
i is 3
i is 4
i is 5

Answer 2

Try this:

#!/bin/bash
echo it starts

i=1
while [ $i -le 5 ]; do
  echo i is $i
  i=$(( i+1 ))
done

Sample output:

it starts
i is 1
i is 2
i is 3
i is 4
i is 5

Here is a great reference:

BASH Programming - Introduction HOW-TO

Answer 3

you should use Visual Studio Code with some extensions to check bash script syntax. I use Vscode in Window 10 WSL2 to run bash script.

change (...) to ((...)) to fix error syntax:

#!/bin/bash
a=5

while ((a > 0)); do
    echo "a = $a"
    a=$((a - 1))
done