ESSENTIAL COMMANDS POCKET GUIDE Fedora LINUX
ESSENTIAL COMMANDS POCKET GUIDE LINUX Covers Fedora Linux DANIEL J. BARRETT … No match was found… 1…so return code is “failure” The return codes of a command are … 168| Linux Pocket Guide Programming with Shell Scripts Earlier when we covered the shell ( bash ), we said it hada programming language built in. In fact, you can write programs, or shell scripts , to accomplish tasks that asinglecom- mandcannot. Like any good programming language, the shell has variables, conditionals (if-then-else), loops, …
Programming with Shell Scripts Earlier when we covered the shell ( bash ), we said it hada programming language built in. In fact, you can write programs, or shell scripts , to accomplish tasks that asinglecom- mandcannot. Like any good programming language, the shell has variables, conditionals (if-then-else), loops, input and output, and more. Entire books have been written on shell scripting, so we’llbecoveringthe bare minimum to get you started. For full documentation, run info bash . Whitespace and Linebreaks bash shell scripts are very sensitive towhitespaceand line- breaks. Because the “keywords”of this programming lan- guageareactually commands evaluated by the shell, you need to separate arguments withwhitespace. Likewise, a linebreakinthe middle of a command will mislead the shell into thinking the command is incomplete. Follow the conventions we present here and you should be fine. Variables We described variables earlier: $ MYVAR=6 $ echo $MYVAR 6 All values held in variables are strings, but if they are numeric the shell will treat them as numbers when appropriate. $ NUMBER=”10″ $ expr $NUMBER + 5 15 When you refer to a variable’svalueinashell script, it’sa good idea to surround it with double quotes to prevent cer- tainruntime errors. An undefined variable, ora variable with spaces in its value, will evaluate to something unexpected if not surrounded by quotes, causing your script to malfunction. $ FILENAME=”My Document” Space in the name $ ls $FILENAME Try to list it
