使用printf在bash中格式化多行命令输出

Question

My Bash script uses printf to print output of some other commands with formatting applied, in the following manner (note the two leading spaces):

printf "  %-16s %s\n" "foo:" "$(bar)"

The two leading spaces are there, because the first line in the file is a comment, and I like to keep things nicely aligned:

# foo
  foo:            bar
  foo:            bar
  ...

This works perfectly fine for commands with one-line output. However, when the output is multiline, the output looses the formatting of the subsequent lines.

For example:

printf "  %-16s %s\n" "Contents:" "$(ls -a)"

Results in something like this:

  Contents:       .
..
foo
bar

Instead, what I am trying to achieve is multiline output, with each line formatted (in columns, if you like), which would look like this (note the lack of "header" in the subsequent lines):

  Contents:       .
                  ..
                  foo
                  bar

My understanding so far is that printf with two arguments (the first one being a string, and the other one the result of the given command) treats the second argument as a single string, which can include newline characters within. Therefore, the output is actually correctly formatted, according to what I asked printf to do, but it is not what I am looking for.

I am aware about some of the pitfalls related to parsing the output of commands like ls , which exhausts my current possibilities of solving this problem. Also, it is possible that printf is not the best facility to do this.

I am considering substituting multiline string into comma-separated list, if no solution to this problem is possible, but this would be a last resort.

What would be the best method to achieve the formatting I need?

Thanks for your help.

Answer 1

printf "  %-16s %s\n" "foo:" "$(bar | sed '2,$s/^/                   /g')"

Answer 2

You may find it difficult to apply the same print instructions to a range of commands. Also output from ls can be tedious to examine because it selects an output format depending upon environment variables.

I found the following worked well for ls on my Mac:

x=$(ls -a); 
x=${x//$'\n'/$'\n'                    }; 
printf "   %-16s %s" "Contents:" "$x" $'\n'