The eval Command The eval command reads and executes commands using the following format: eval commands It causes commands to be expanded twice. For simple commands, there is no difference in execution with or without eval: $ eval print ~ /home/anatole Here is a more complicated command that illustrates the use of eval. We want the contents of the stext file redirected when variable X is accessed. $ cat stext She sells seashells by the seashore. First, variable X is set to "<stext": $ X="<stext" When the value of X is printed using simple variable expansion, it generates an error: $ cat $X <stext: No such file or directory Using the eval command, X is first expanded to <stext, then the command cat <stext is executed. This causes the contents of stext to be displayed: $ eval cat $X She sells seashells by the seashore. In this Korn shell script, the eval command is used to display the last command-line argument: $ cat eval_test print "Total command-line arguments is $#" print "The last argument is $$#" What you want is $# to be expanded first to the number of arguments, then $n to be expanded to the value of the last argument. Without the eval command, this is the output of eval_test: $ eval_test a b c Total command-line arguments is 3 The last argument is 581# The output 581# is generated because $$ is first expanded to the process id. Using the eval command to expand the print command twice, we get the correct result. $ cat eval_test print "Total command-line arguments is $#" print "The last argument is $(eval print \$$#)" $ eval_test1 a b c The number of command-line arguments is 3 The last argument is c The \ is needed so that the $ character is ignored on the first expansion. After the first expansion, the $(eval print \$$#) command becomes $(print $3). This is then expanded to c. | 
