using linux how can I pass the contents of a file as a parameter to an executable?

Question

let's say I want to run ./program with a string argument

instead of typing ./program string each time, how can I do ./program <file> where <file> is a file that contains string?

thankyou

Answer 1

This should do the trick:

./program `cat file` 

If you want the entire file content in a single argument, add double quotation (tested in bash. I think It may vary shell to shell) :

./program "`cat file`"  

Answer 2

Command

./program "$(< file)" 

Explanation

1. $(cmd) runs a command and converts its output into a string. $(cmd) can also be written with backticks as `cmd`. I prefer the newer $(cmd) as it nests better than the old school backticks.

2. The command we want is cat file. And then from the bash man page:

   The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

3. The quotes around it make sure that whitespace is preserved, just in case you have spaces or newlines inside of your file. Properly quoting things in shell scripts is a skill that is sorely lacking. Quoting variables and command substitutions is a good habit to good into so you don't get bit later when your file names or variable values have spaces or control characters or other weirdnesses.