Shell Scripting

User-Defined Functions You can create user-defined functions in a awk script file using the func or function keywords. Placement in the file is not important; the function definition can occur anywhere in the awk script. The function can take arguments (local to the function only) or use any existing variable. The syntax of a function definition is: func function_name ([optional_arg] . . .) { statements } or function function_name ([optional_arg] . . .) { statements } The … [Read more...] about How to Use user-defined Functions in awk

The awk programming language contains many of the programming concepts that are used in shell scripting. Conditionals, such as the if statement and loops, such as the following can also be used in awk programming. The while loop The do while loop The for loop The if Statement The if statement can have two branches: an if branch and an else branch. If the condition is true, the if branch is executed; if the condition is false, the else branch is executed. if (condition) { … [Read more...] about Using Loops (while, for) in awk scripts

Shell Signal Values A signal is a message that some abnormal event has taken place or a message requesting another process do something. The signal is sent from one process to another process. Typically, a process sends a signal to one of its own subprocesses. You can obtain more information on signals from the signal and kill man pages. You use the kill command to send signals to processes. The root user can send any signal to any process. Other users can only send signals to processes they … [Read more...] about Beginners Guide to Using “trap” to Catch Signals and Handle Errors in Shell Script

Creating Bourne Shell Constants A variable can be made read-only with the following syntax: readonly var[=value] The square brackets around =value mean that the assignment of a value is not always necessary. For instance, if the variable had previously been created and assigned a value, and you now want to make it read-only (and not change its current value), do not use =value. If the variable did not previously exist, and you make it read-only, you may never assign a value to the … [Read more...] about How to Make a Variable read-only (constant) in Bash and Korn Shell

The shift Statement Sometimes a script does not require a specific number of arguments from users. Users are allowed to give as many arguments to the script as they want. In these situations, the arguments of the script are usually processed in a while loop with the condition being (($#)). This condition is true as long as the number of arguments is greater than zero. Within the script $1 and the shift statement process each argument. Because doing a shift reduces the argument number, … [Read more...] about Examples of “shift” Command in Shell Scripts

The select statement in the Korn shell creates a menu. This construct is for the Korn shell only. The syntax for creating a menu is: select var in list do statement1 ... statementN done The variables var and list follow the same syntactic rules used in the for loop (although the operation of the select loop is substantially different). If the list contains metacharacters, the metacharacters are expanded into file names. The elements in the list are the menu … [Read more...] about Korn Shell select Loop