Unix in a Nutshell, 4th 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. (Even if expr is false, any redirection in cmd 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 the section "Expressions" 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