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Accepted
Tom Brossman
Asked: 2017-02-24 06:36:58 +0800 CST

Generate multiple Bash options from a text file?

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I have a command that takes domain names as options. I have a long list of domain names to include and so I'd like to automate the parsing of that list of domains into the command.

For example, the simplest usage would be command --option=example-one.com --output=file.ext. After adding the list of domains the eventual command to execute would look like command --option=example-one.com ... --option=example-99.io --output=file.ext (where '...' would be 97 more options, shown abbreviated here)

Is this possible to do in Bash and if yes, what's it called please?

Here's what I tried that didn't work so far:

  1. command --option=$(cat domains.txt) --output=file.ext
  2. command "$(while read baddomains ; do echo -n '--option=$baddomains ' ; done < domains.txt)" --output=file.ext
  3. command --option="domains.txt" --output=file.ext

The command while read baddomains ; do echo -n '--option=$baddomains ' ; done < domains.txt > all-options.txt does output a list of perfectly formatted options into a new file all-options.txt, but I can't understand how to redirect output of the options back into the command, instead of a text file.

The list of domains includes Cyrillic characters, if that matters.

bash options

2 Answers

  1. You can build an array with the arguments:

    args=()
while read -r domain _; do
    args+=("--option=$domain")
done < domains.txt

command "${args[@]}" --output=file.ext
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  2. Best Answer
    command $(printf -- "--option=%s " $(<domains.txt)) --output=file.ext

    is the most compact way I know.

    What you were trying should have been

    command $(while read baddomains ; do echo -n "--option=$baddomains " ; done < domains.txt) --output=file.ext

    but it didn’t work for you because you used the wrong quotes in the subshell, and enclosed the whole $() in double quotes, so that command saw the whole as one argument.

    The list of domains includes Cyrillic characters, if that matters.

    It doesn’t matter to these commands, but, if they are not properly punycoded, how can they be valid domain names? If they are punycoded, the shell will see no cyrillic characters whatsoever. It will happily process its input correctly in both cases.

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