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Accepted
genderbee
Asked: 2019-09-13 03:02:38 +0800 CST

How can I import output from a command as a command in Bash?

  • 772

System

Linux hosek 4.15.0-48-generic #51-Ubuntu SMP Wed Apr 3 08:28:49 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Issue

I need to get output as commands, in a bash script, for storing variables.

Example

sed -n '/# Main configuration./,/# Websites./p' webcheck-$category.cfg | sed '1,1d' | sed '$ d'

This command returns these lines:

email_sender='[email protected]'
email_recipients='[email protected]'

How can I read/run these output/lines as commands in script? Is storing this output to the file and then read it by source command only way?

I tried | source at the end of the command, but it reads only from files.

I tried echo at the beginning, but that had no effect.

Thanks.

command-line bash

4 Answers

  1. Best Answer

    As pLumo showed you, you can indeed source them. However, I would recommend against this. If you have something like this:

    source <(sed -n '/# Main configuration./,/# Websites./p' webcheck-$category.cfg | sed '1,1d' | sed '$ d')

echo "$email_sender"

    Then, a year later when you come back and look at this script, you will have no idea where this email_sender variable is coming from. I suggest you instead change the command and use one that returns only the variable's value and not its name. That way, you can easily keep track of where each variable comes from:

    email_sender=$(grep -oP 'email_sender=\K.*' webcheck-$category.cfg)
email_recipients=$(grep -oP 'email_recipients=\K.*' webcheck-$category.cfg)
    • 15

  2. You can use process substitution:

    source <(sed -n '/# Main configuration./,/# Websites./p' webcheck-$category.cfg | sed '1,1d' | sed '$ d')
    • 3 
  3. #!/bin/bash

declare -A data
while IFS='=' read -r key value; do
    data[$key]=${value//\'/}
done < <(grep -E '^([^#].+=.*)' webcheck-$category.cfg)

    or

    done < <(sed -n '/# Main configuration./,/# Websites./{//!p}' webcheck-$category.cfg)

    # associative array.
echo ${data[email_sender]}
echo ${data[email_recipients]}

    Output:

    [email protected] [email protected]

    • 0

  4. bash read builtin handles things like this nicely.

    read -d '' -r email_sender email_recipients < <(
  grep -oP 'email_sender=\K.*' webcheck-$category.cfg; 
  grep -oP 'email_recipients=\K.*' webcheck-$category.cfg
)

    read reads lines from stdin into variables. -d '' turns off whitespace splitting, except for newlines. -r disables \ escapes.

    cmdA < <(cmdB) works similarly to cmdB | cmdA, except in the former cmdA is run in ~this~ shell, instead of a subshell, which is required for read to work as expected.

    • -1