In linux if I want to redirect standard error to a file, I can do this:
$ls -l /bin/usr 2> ls-error.txt
But when I try:
$foo=
$echo ${foo:?"parameter is empty"} 2> ls-error.txt
The result in terminal is:
bash: foo: parameter is empty
It doesn't work!
Can somebody explain why?
I thought ${parameter:?word} would send the value of word to standard error.
echo ${foo:?"parameter is empty"} 2>ls-error.txt redirects the stderr of echo, but the error message is produced by the shell while expanding
${foo:?"parameter is empty"}.
You can get the result you want by redirecting a block (or a subshell) instead so that the shell's stderr is included in the redirection:
{ echo "${foo:?"parameter is empty"}"; } 2>ls-error.txt
Try this command: ($echo ${foo:?"parameter is empty"}) 2> ls-error.txt
In case you would like to redirect both sandard and error output, AND to still get these messages when executing your command, you can use the tee command:
$echo ${foo:?"parameter is empty"} |& tee -a ls-error.txt
