see this

cat < Files
return the cointent of Files

but

cat files

return the same result


WHI???


this command

lp -f """PRINTER" < cat files

not print the content of files

WHI ???

i not understand the use of <

every process has three default file descriptors open when it starts

0 - stdin
1 - stdout
2 - stderr

the ">" operator creates a file and attaches it to stdout
the ">>" opens a file for appending and attaches it to stdout
the "<" opens an existing file and attaches it to stdin
the "|" attaches the stdout of the preceding process to the stdin of the following

The program cat "concatenates" a list of files given as arguments to stdout, if no files are listed it simply reads from stdin and writes that to stdout.