By Cooper M.
This educational assumes no prior wisdom of scripting or programming, yet progresses speedily towards an intermediate/advanced point of guideline ...all the whereas sneaking in little snippets of UNIX knowledge and lore. It serves as a textbook, a guide for self-study, and a reference and resource of data on shell scripting suggestions. The workouts and heavily-commented examples invite lively reader participation, less than the basis that the one solution to quite research scripting is to put in writing scripts.
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Additional resources for Advanced Bash−Scripting Guide. An in−depth exploration of the gentle art of shell scripting
Work. echo exit 0 Example 7−6. sh: Testing null strings and unquoted strings, # but not strings and sealing wax, not to mention cabbages and kings... # Using if [ ... ] # If a string has not been initialized, it has no defined value. # This state is called "null" (not the same as zero). if [ −n $string1 ] # $string1 has not been declared or initialized. " fi # Wrong result. # Shows $string1 as not null, although it was not initialized. echo # Lets try it again. if [ −n "$string1" ] # This time, $string1 is quoted.
Bin/bash echo hello echo $? # Exit status 0 returned because command executed successfully. lskdf echo $? # Unrecognized command. # Non−zero exit status returned because command failed to execute. echo exit 113 # Will return 113 to shell. " after script terminates. # By convention, an 'exit 0' indicates success, #+ while a non−zero exit value means an error or anomalous condition. $? is especially useful for testing the result of a command in a script (see Example 12−27 and Example 12−13). , the logical "not" qualifier, reverses the outcome of a test or command, and this affects its exit status.
Fi echo exit 0 The bracket notation for positional parameters leads to a fairly simply way of referencing the last argument passed to a script on the command line. This also requires indirect referencing. args} # Number of args passed. $#} doesn't work. Some scripts can perform different operations, depending on which name they are invoked with. For this to work, the script needs to check $0, the name it was invoked by. There must also exist symbolic links to all the alternate names of the script.