shell: How to capture stderr output depending on a flag

Question

Someone would be able to help me with the TODO in shell/bash which can be seen at

https:// github.com/davorpa/shell-utils/commit/230f71a9b2400acc24a7e92889b17bb8cd8b21a4#diff-6c619df767c9a45741832bd40be5d60ba2b2b2b45741832bd40bed6024ba2b1

Is there some approach to capture the output in a local variable or with pipes and conditionally print it afterwards?

I have already tried many ways like with command substitution and pipes, but the original output loses colors... escapes. With file descriptors I still do not clarify very well and I always fail.

Thanks for support

Answer 1

Yes, there are some ways to capture the output of a command bro. Most of extern commands output something to stdout (Standard Output).

You can capture that output, for example, for example, using `` and the command inside of them.

For example:

output=`echo "hi to everybody"`
echo "$output"

Output:
Hi to everybody

Hope this help you, if you're still facing problems, you can DM me, and I will help you😊😀

Answer 2

I've read a lot about theory but not fresh with practice and always failing

- normal

local ecode;
( my-cmd "arg" ) && ecode=$? || ecode=$?

- command substitution. $() or legacy ``

local output;
output=$(my-cmd "arg")
local ecode=$?
echo -e "$ecode $output"
printf '%s %s\n' "$ecode" "$output"

- raw eval / exec

eval "$@"
exec "$0" "$@"

- redirect file descriptors:

my-cmd "arg" 2>/dev/null #ignore stderr
my-cmd "arg" >> file.txt #append all 2 file

- temp fds: 😖

{ var="$( { my-cmd; } 2>&1 1>&3 3>&- )"; } 3>&1;

- pipes

my-cmd "arg" | tee ...

- descriptor context exec (😲bashismo)

local var;
my-cmd "arg" 2> >( read var <<<&1 )

three first is the unique I know use more or less fine.

With command substitution I see in my terminal that colors send by original command are lost. it's rare because new lines don't.

with pipes I lost exit code of my-cmd

I misunderstand the others: syntax, advantages/disadvantages

too much to learn 😥

Answer 3

I will try this... with temporal file-descriptors

https://unix.stackexchange.com/questions/474177/how-to-redirect-stderr-in-a-variable-but-keep-stdout-in-the-console

Answer 4

Yes, that's correct bro👍😀