I have a script that may in some circumstances have nothing on stdout. At the end of the script, I pass the lines I have to another command using xargs. My problem is, when there is nothing on stdout, I get the typical "Usage: program arg1 arg2" error message.
How can I avoid this?
You need an -r or --no-run-if-empty options.
Keep in mind that this particular behavior is hard to make cross-platform.
BSD versions of xargs run with -r by default. GNU version needs it. FreeBSD version of xargs ignores -r flag for compatibility with GNU. Mac OS X version does not even accept the flag and throws an error illegal option.
You might then choose to use an OS detection based on $OSTYPE to write a cross-platform script.
Even better, try to detect the behavior of xargs itself. Run it with -r and if that fails (status code > 0), run it without -r.
A lesson in why you should read the man pages…
The -r or --no-run-if-empty flags are my friend.
