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Full Discussion: $(< file ) and $( cat file )
Top Forums Shell Programming and Scripting $(< file ) and $( cat file ) Post 303012378 by Scrutinizer on Saturday 3rd of February 2018 01:12:05 AM
Old 02-03-2018
It does not work that way. $(<file) is a special case, which is a faster alternative to $(cat file). If you are using anything other than just a file, it becomes something else. $( ... ) is just command sustitution, so if we leave out that, it becomes:
Code:
< /dev/urandom tr -dc '[:alnum:],@#:!?+-' | head -c10

This is the same as tr -dc '[:alnum:],@#:!?+-' < /dev/urandom | head -c10
Code:
cat /dev/urandom -- tr -dc '[:alnum:],@#:!?+-' | head -c10

This is strange, it effectively just means cat /dev/urandom | head -c10
Code:
cat /dev/urandom | tr -dc '[:alnum:],@#:!?+-' | head -c10

This is the same as the first one with UUOC
Code:
< /dev/urandom | tr -dc '[:alnum:],@#:!?+-'  | head -c10

This is equivalent to :< /dev/urandom | tr -dc '[:alnum:],@#:!?+-' | head -c10, which is that same as :
: | tr -dc '[:alnum:],@#:!?+-' | head -c10
This User Gave Thanks to Scrutinizer For This Post:
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