Here's a simplified version with extended explanation for beginners like me who are trying to learn how to put more than one command in one line.
If you were to write out the problem in steps, it would look like this:
// For every file in this directory
// Check the filetype
// If it's an ASCII file, then print out the filename
To achieve this, we can use three UNIX commands: find
, file
, and grep
.
find
will check every file in the directory.
file
will give us the filetype. In our case, we're looking for a return of 'ASCII text'
grep
will look for the keyword 'ASCII' in the output from file
So how can we string these together in a single line? There are multiple ways to do it, but I find that doing it in order of our pseudo-code makes the most sense (especially to a beginner like me).
find ./ -exec file {} ";" | grep 'ASCII'
Looks complicated, but not bad when we break it down:
find ./
= look through every file in this directory. The find
command prints out the filename of any file that matches the 'expression', or whatever comes after the path, which in our case is the current directory or ./
The most important thing to understand is that everything after that first bit is going to be evaluated as either True or False. If True, the file name will get printed out. If not, then the command moves on.
-exec
= this flag is an option within the find command that allows us to use the result of some other command as the search expression. It's like calling a function within a function.
file {}
= the command being called inside of find
. The file
command returns a string that tells you the filetype of a file. Regularly, it would look like this: file mytextfile.txt
. In our case, we want it to use whatever file is being looked at by the find
command, so we put in the curly braces {}
to act as an empty variable, or parameter. In other words, we're just asking for the system to output a string for every file in the directory.
";"
= this is required by find
and is the punctuation mark at the end of our -exec
command. See the manual for 'find' for more explanation if you need it by running man find
.
| grep 'ASCII'
= |
is a pipe. Pipe take the output of whatever is on the left and uses it as input to whatever is on the right. It takes the output of the find
command (a string that is the filetype of a single file) and tests it to see if it contains the string 'ASCII'
. If it does, it returns true.
NOW, the expression to the right of find ./
will return true when the grep
command returns true. Voila.