Java™ Application Development on Linux - Dator

18Chapter 1An Embarrassment of Riches: The Linux Environmentfor your input. You can press the space bar to get the next screen’s worth ofoutput. You can type a slash, then a string, and it will search forward for thatstring. If you have gone farther forward in the file than you wanted, press “b”to go backwards.To find out more about the many, many commands available, press ?(the question mark) while it’s running.Typical uses for these commands are:• To view one or more files, for example more *.java, where you can type:n to skip to the next file.• To page through long output from a previous pipe of commands, for example,$ grep Account *.java | more, which will search (see moreon grep below) for the string Account in all of the files whose names endin .java and print out each line that is found—and that output will bepaginated by more.If you need only to check the top few lines of a file, use head. You canchoose how many lines from the front of the file to see with a simple parameter.The command head -7 will write out the first seven lines, then exit.If your interest is the last few lines of a file, use tail. You can choose howmany lines from the end of the file to see; the command tail -7 will writeout the last seven lines of the file. But tail has another interesting parameter,-f. Though tail normally prints its lines and then, having reached the end offile, it quits, the -f option tells tail to wait after it prints the last few lines andthen try again. 7 If some other program is writing to this file, then tail will, onits next read, find more data and print it out. It’s a great way to watch a log file,for example, tail -f /tmp/server.log.In this mode, tail won’t end when it reaches the end of file, so when youwant it to stop you’ll have to manually interrupt it with a ^C (Control-C— i.e.,hold down the Control key and press the C key).disclosure, there is also a paging program called pg, the precursor to more, but we’ll say nomore about that.7. The less command has the same feature. If you press “F” while looking at a file, it goes intoan identical mode to the tail -f command. As is often the case in the wacky world of Linux,there is more than one way to do it.