I think you want to capture stderr, stdout and exitcode if that is your intention you can use this code:
## Capture error when 'some_command() is executed
some_command_with_err() {
echo 'this is the stdout'
echo 'this is the stderr' >&2
exit 1
}
run_command() {
{
IFS=$'\n' read -r -d '' stderr;
IFS=$'\n' read -r -d '' stdout;
IFS=$'\n' read -r -d '' stdexit;
} < <((printf '\0%s\0%d\0' "$(some_command_with_err)" "${?}" 1>&2) 2>&1)
stdexit=${stdexit:-0};
}
echo 'Run command:'
if ! run_command; then
## Show the values
typeset -p stdout stderr stdexit
else
typeset -p stdout stderr stdexit
fi
This scripts capture the stderr, stdout as well as the exitcode.
But Teo how it works?
First, we capture the stdout as well as the exitcode using printf '\0%s\0%d\0'. They are separated by the \0 aka 'null byte'.
After that, we redirect the printf to stderr by doing: 1>&2 and then we redirect all back to stdout using 2>&1. Therefore, the stdout will look like:
"<stderr>\0<stdout>\0<exitcode>\0"
Enclosing the printf command in <( ... ) performs process substitution. Process substitution allows a process’s input or output to be referred to using a filename. This means <( ... ) will pipe the stdout of (printf '\0%s\0%d\0' "$(some_command_with_err)" "${?}" 1>&2) 2>&1into the stdin of the command group using the first <.
Then, we can capture the piped stdout from the stdin of the command group with read. This command reads a line from the file descriptor stdin and split it into fields. Only the characters found in $IFS are recognized as word delimiters. $IFS or Internal Field Separator is a variable that determines how Bash recognizes fields, or word boundaries, when it interprets character strings. $IFS defaults to whitespace (space, tab, and newline), but may be changed, for example, to parse a comma-separated data file. Note that $* uses the first character held in $IFS.
## Shows whitespace as a single space, ^I(horizontal tab), and newline, and display "$" at end-of-line.
echo "$IFS" | cat -vte
# Output:
# ^I$
# $
## Reads commands from string and assign any arguments to pos params
bash -c 'set w x y z; IFS=":-;"; echo "$*"'
# Output:
# w:x:y:z
for l in $(printf %b 'a b\nc'); do echo "$l"; done
# Output:
# a
# b
# c
IFS=$'\n'; for l in $(printf %b 'a b\nc'); do echo "$l"; done
# Output:
# a b
# c
That is why we defined IFS=$'\n' (newline) as delimiter.
Our script uses read -r -d '', where read -r does not allow backslashes to escape any characters, and -d '' continues until the first character '' is read, rather than newline.
Finally, replace some_command_with_err with your script file and you can capture and handle the stderr, stdout as well as the exitcode as your will.
