2
The name
argv
is a nod to the C language. The v is for vector, which is similar to an array.
const
fs
=
require
(
'fs'
);
fs
.
readdir
(
'data'
,
function
(
err
,
files
) {
if
(
err
) {
console
.
error
(
"Fatal error: couldn't read data directory."
);
process
.
exit
(
1
);
}
const
txtFiles
=
files
.
filter
(
f
=>
/\.txt$/i
.
test
(
f
));
if
(
txtFiles
.
length
===
0
) {
console
.
log
(
"No .txt files to process."
);
process
.
exit
(
0
);
}
// process .txt files...
});
The
process
object also gives you access to an array containing the command-line
arguments passed to the program. When you execute a Node application, you can
provide optional command-line arguments. For example, we could write a program
that takes multiple filenames as command-line arguments, and print out the number
of lines of text in each file. We might invoke the program like this:
$ node linecount.js file1.txt file2.txt file3.txt
The command-line arguments are contained in the
process.argv
array.
count the lines in our files, let’s print out
process.argv
so we know what we’re get‐
ting:
console
.
log
(
process
.
argv
);
Along with file1.txt, file2.txt, and file3.txt, you’ll see a couple of extra elements at the
beginning of the array:
[
'node'
,
'/home/jdoe/linecount.js'
,
'file1.txt'
,
'file2.txt'
,
'file3.txt'
]
The first element is the interpreter, or program that interpreted the source file (
node
,
in our case). The second element is the full path to the script being executed, and the
rest of the elements are any arguments passed to the program. Because we don’t need
this extra information, we’ll just use
Array.slice
to get rid of it before counting the
lines in our files:
const
fs
=
require
(
'fs'
);
const
filenames
=
process
.
argv
.
slice
(
2
);
292 | Chapter 20: Node
