On Mon, Nov 5, 2018 at 7:51 AM Mike Wright <nobody@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> There is such a thing as too terse. Can somebody explain what this
> cryptic snippet means? I get the "substitute part; it's the
> "error,exit" part that has me confounded.
>
> +------------------+--------------------+---------------+--------------+
> | | parameter | parameter | parameter |
> | | Set and Not Null | Set But Null | Unset |
> +------------------+--------------------+---------------+--------------+
> |${parameter:?word}|substitute parameter|error,exit |error,exit |
> |${parameter?word} |substitute parameter|substitute null|error,exit |
> +------------------+--------------------+---------------+--------------+
In the case of ":?word" and "unset", for example, it'll print "word",
and exit the script if it's running within a script.
th macbook12 ~ $ bash --version
GNU bash, version 4.4.23(1)-release (x86_64-apple-darwin18.0.0)
...
th macbook12 ~ $ echo ${PS1:?fedora}
\u \h \w $
th macbook12 ~ $ echo ${PS5:?fedora}
-bash: PS5: fedora
th macbook12 ~ $ vi mike.sh
th macbook12 ~ $ chmod +x mike.sh
th macbook12 ~ $ cat mike.sh
#!/bin/sh
one=ONE
three=THREE
echo "print one"
echo ${one:?fedora}
echo
echo "print two"
echo ${PS5:?fedora}
echo
echo "print three"
echo ${three}
th macbook12 ~ $ ./mike.sh
print one
ONE
print two
./mike.sh: line 8: PS5: fedora
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