To understand xargs better

Question

I want to understand the use of xargs man in Rampion\'s code:

screen -t man /bin/sh -c \'xargs man || read\'

Thanks to Ram

Answer 1

The cat command does not operate on nothing; it operates on standard input, up until it is told that the input is ended. As Rampion notes, the cat command is not necessary here, but it is operating on its implicit input (standard input), not on nothing.

The xargs command reads the output from cat, and groups the information into arguments to the man command specified as its (only) argument. When it reaches a limit (configurable on the command line), it will execute the man command.

The find ... -print0 | xargs -0 ... idiom deals with file names that contain awkward characters such as blanks, tabs and newlines. The find command prints each filename followed by an ASCII NUL ('\0'); this is one of two characters that cannot appear in a simple file name - the other being '/' (which appears in path names, of course, but not in simple file names). It is not directly equivalent to the sequence you provide; xargs groups collections of file names into a single argument list, up to a size limit. If the names are short enough (they usually are), then there will be fewer executions of grep than there are file names.

Note, too, the grep only prints the file name where the material is found if it has more than one file to search -- or if it supports an option so that it always prints the file names and the option is used: '-H' is a GNU extension to grep that does this. The portable way to ensure that the file names always appear is to list /dev/null as the first file (so 'xargs grep something /dev/null'); it doesn't take long to search /dev/null.