echo “string” > file in Windows PowerShell appends

问题:

In Windows PowerShell:

echo "string" > file.txt

In Cygwin:

$ cat file.txt
:::s t r i n g

$ dos2unix file.txt
dos2unix: Skipping binary file file.txt

I want a simple "string" in the file. How do I do it? I.e., when I say cat file.txt I need only "string" as output. I am echoing from Windows PowerShell and that cannot be changed.

回答1:

Try echo "string" | out-file -encoding ASCII file.txt to get a simple ASCII-encoded txt file.

Comparison of the files produced:

echo "string" | out-file -encoding ASCII file.txt

will produce a file with the following contents:

73 74 72 69 6E 67 0D 0A (string..)

however

echo "string" > file.txt

will produce a file with the following contents:

FF FE 73 00 74 00 72 00 69 00 6E 00 67 00 0D 00 0A 00 (ÿþs.t.r.i.n.g.....)

(Byte order mark FF FE indicates the file is UTF-16 (LE). The signature for UTF-16 (LE) = 2 bytes: 0xFF 0xFE followed by 2 byte pairs. xx 00 xx 00 xx 00 for normal 0-127 ASCII chars

回答2:

These two commands are equivalent in that they both use UTF-16 encoding by default:

echo "string" > file.txt
echo "string" | out-file file.txt

You can add an explicit encoding parameter to the latter form (as indicated by jon Z) to produce plain ASCII:

echo "string" | out-file -encoding ASCII file.txt

Alternately, you could use set-content, which uses ASCII encoding by default:

echo "string" | set-content file.txt

---

Corollary 1:

Want to convert a unicode file to ASCII in one line?

Just use this:

get-content your_unicode_file | set-content your_ascii_file

which can be abbreviated to:

gc your_unicode_file | sc your_ascii_file

---

Corollary 2:

Want to get a hex dump so you can really see what is unicode and what is ASCII?

Use the clean and simple Get-HexDump function available on PowerShell.com. With that in place you can examine your generated files with just:

Get-HexDump file.txt

For anything non-trivial, you can specify how many columns wide you want the output and how many bytes of the file to process with something like this:

Get-HexDump file.txt -width 15 -bytes 150

回答3:

PowerShell creates Unicode UTF-16 files with a Byte Order Mark (BOM).

Dos2unix 6.0 and higher can read UTF-16 files and convert them to UTF-8 (the default Cygwin encoding) and remove the BOM. Versions prior to 6.0 will see UTF-16 files as binary and skip them, as in your example.