In my script I have this line:
[ -z "$(file $1 | grep '256')" ] && echo 256
If $1 contains spaces, then I get the error message
line 11: [: too many arguments
How can I properly quote this so that it is runs correctly?
UPDATE:
I pasted the line from my script incorrectly. The error message is correct for this line
[ -z $(file "$1" | grep '256') ] && echo 256
Double quote the $1:
[ -z "$(file "$1" | grep '256')" ] && echo 256
PS: The line you posted would not cause the error you're referring to. Either you copied the error from another version, or you have another misquoted line in your script.
$(...) gets evaluated first, then the parent shell's quoting is processed.Use double quotes around your variables. Always.
(Well, not always always. There are situations where you want the shell to perform word splitting on a value, but those are a small minority and not something you should expect to understand any time soon.)
However, what you are doing there can simply be replaced with
file "$1" | grep -o '256'
Shell quoting is a common FAQ; it's poorly understood, but not hard at all. See e.g. http://mywiki.wooledge.org/Quotes (Bash-specific, but generally applicable to the entire Bourne family of shells.)
