By Cooper M.
The complex Bash Scripting advisor is either a reference and an educational on shell scripting. This accomplished e-book (the identical of approximately 646 print pages) covers virtually each point of shell scripting. It comprises over three hundred profusely commented illustrative examples, and a few tables. not only a shell scripting educational, this booklet additionally offers an creation to uncomplicated programming thoughts, reminiscent of sorting and recursion. it really is well matched for both person examine or lecture room use.
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Extra info for Advanced Bash-Scripting Guide. A complete guide to shell scripting
Echo exit 0 Example 7−5. 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, $string1 is quoted.
Fi echo xyz= Chapter 7. Tests # Initialized, but set to null value. " fi echo # When is "false" true? echo "Testing \"false\"" if [ "false" ] # It seems that "false" is just a string. " #+ and it tests true. " fi echo echo "Testing \"\$false\"" # Again, uninitialized variable. " fi # Now, we get the expected result. echo exit 0 Exercise. Explain the behavior of Example 7−1, above. if [ condition−true ] then command 1 command 2 ... else # Optional (may be left out if not needed). # Adds default code block executing if original condition tests false.
Give different results. echo echo '$hello' # Variable referencing disabled by single quotes, #+ which causes the "$" to be interpreted literally. # Notice the effect of different types of quoting. hello= # Setting it to a null value. echo "\$hello (null value) = $hello" # Note that setting a variable to a null value is not the same as #+ unsetting it, although the end result is the same (see below). # −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− # It is permissible to set multiple variables on the same line, #+ if separated by white space.