Linux in a Nutshell, Fourth Edition

Name

if

Synopsis

                  if
               

Begin a conditional statement. The simple format is:

if (expr) cmd

There are three other possible formats, shown side by side:

if (expr) then   if (expr) then   if (expr) then
   cmds             
                  cmds1             
                  cmds1
endif            else             else if (expr) then
                    cmds2             
                  cmds2
                 endif            else
                                      cmds3
                                  endif

In the simplest form, execute cmds if expr is true, otherwise do nothing. (Redirection still occurs; this is a bug.) In the other forms, execute one or more commands. If expr is true, continue with the commands after then; if expr is false, branch to the commands after else or else if and continue checking. For more examples, see Section 8.5 earlier in this chapter, or the shift or while commands.

Example

Take a default action if no command-line arguments are given:

                  if ($#argv =  = 0) then
                     echo "No filename given. Sending to Report."
                     set outfile = Report
                  else
                     set outfile = $argv[1]
                  endif