regex - Why is Bash pattern match for ?(*[[:class:]])foobar slow? -

i have text file foobar.txt around 10kb, not long. yet following match search command takes 10 seconds on high-performance linux machine.

bash>shopt -s extglob bash>[[ `cat foobar.txt` == ?(*[[:print:]])foobar ]] 

there no match: characters in foobar.txt printable there no string "foobar".

the search should try match 2 alternatives, each of them not match:

"foobar" 

that's instantenous

*[[:print:]]foobar 

- should go this:

should scan file character character in 1 pass, each time, check if next characters

[[:print:]]foobar 

this should fast, no way should take millisecond per character.

in fact, if drop ?, is, do

bash>[[ `cat foobar.txt` == *[[:print:]]foobar ]] 

this is instantaneous. second alternative above, without first.

so why long??

as others have noted, you're better off using grep.

that said, if wanted stick [[ conditional - combining @konsolebox , @rici's advice - you'd get:

[[ $(<foobar.txt)  =~ (^|[[:print:]])foobar$ ]] 

edit: regex updated match op's requirements - thanks, @rici.

generally speaking, preferable use regular expressions string matching (via =~ operator, in case), rather [globbing] patterns (via == operator), primary purpose matching file- , folder names.