Question

Is this normal? I tried it (long story… it all began with poor quoting on something else) with bash, dash and ksh. In all cases I get:

$ echo [:print:][:blank:]
[:print:][:blank:]
$ touch in
$ echo [:print:][:blank:]
in

I thought it had something to do with ‘in’ being a substring of ‘print’, but (say) ‘pr’ doesn’t do it:

$ rm in; touch pr
$ echo [:print:][:blank:]
[:print:][:blank:]

Also, dropping ‘blank’ gets rid of this:

$ touch in; echo [:print:]         
[:print:]

I am completely lost. Thanks in advance for your help!

Answer 1

[:print:][:blank:] is regarded as a glob pattern, so any filenames matching it will be printed, just like when you say echo * (try that in an empty directory).

[:print:] is interpreted as “one of the characters {:,p,r,i,n,t}” and similarly for [:blank:]; hence the match with in, but not pr.

(pr will match [:print:][:print:], though.)