使用Bash将多字串作为卷曲选项

Question

I want to get some data from a HTTP server. What it sends me depends on what I put in a POST request.

What I put in the INPUT_TEXT field is a sequence of words. When I run the following command, I get good looking output.

$ curl http://localhost:59125/process -d INPUT_TEXT="here are some words"

I want a bash script to take some string as a command line argument, and pass it appropriately to curl. The first thing I tried was to put the following in a script:

sentence=$1
command="curl http://localhost:59125/process -d INPUT_TEXT=\"${sentence}\""
$command

I then run the script like so:

$ ./script "here are some words"

But then I get a curl Couldn't resolve host error for each of "are", "some", and "words". It would seem that "here" got correctly treated as the INPUT_TEXT, but the rest of the words were then considered to be hosts, and not part of the option.

So I tried:

command=("curl" "http://localhost:59125/process" "-d" "INPUT_TEXT='$sentence'")
${command[@]}

I got the same output as the first script. I finally got what I wanted with:

result=$(curl http://localhost:59125/process -d INPUT_TEXT="${sentence}")
echo $result

I'm still unsure as to what the distinction is. In the first two cases, when I echoed out the contents of command, I get exactly what I input from the interactive Bash prompt, which had worked fine. What caused the difference?

Answer 1

The following will work:

command=("curl" "http://localhost:59125/process"
         "-d"  "INPUT_TEXT=$sentence")
"${command[@]}"

That has two changes from yours:

• I removed the incorrect quotes around $sentence since you don't want to send quotes to the server (as far as I can see).

• I put double-quotes around the use of "${command[@]}" . Without the double quotes, the array's elements are concatenated with spaces between them and then the result is word-split. With double quotes, the individual array elements are used as individual words.

The second point is well-explained in the bash FAQ and a bunch of SO answers dealing with quotes.

The important thing to understand is that quotes only quote when a command is parsed. A quote which is a character in a variable is just a character ; it is not reinterpreted when the value of the variable expanded. Whitespace in the variable is used for word-splitting if the variable expansion is unquoted; the fact that the whitespace was quoted in the the command which defined the variable is completely irrelevant. In this sense, bash is just the same as any other programming language .