UNIX for OpenVMS Users, Second Edition
A bridge for people switching to UNIX who are familiar with OpenVMS commands and its general operating environment.
TABLE OF CONTENTS UNIX for OpenVMS Users, Second Edition
Section 10.8: Flow Control
10.8 Flow Control
The statements IF-THEN-ELSE-ENDIF, GOSUB-RETURN, CALL, and GOTO provide flow control in OpenVMS command procedures. The UNIX C shell also offers if and goto and the additional statements while, foreach, break, continue, switch, breaksw, and shift to control the logical flow of a shell script. The Korn shell provides if, while, until, for, break, continue, case, select, and shift. As with DCL command procedures, both C shell and Korn shell allow you to exert flow control in response to error conditions (see Section 10.8.12).
10.8.1 if (C and Korn shells)
The if statement provides a one- or two-way conditional branch. You can nest if statements, as the more complex examples in Section 10.11 show.
| VMS | UNIX (C shell) | |
|---|---|---|
| Form: | $ <b class="bold">IF</b> <b class="bold"><i class="emphasis">expression</i></b>$ <b class="bold">THEN</b><b class="bold"><i class="emphasis">command(s)</i></b>$ <b class="bold">ELSE</b><b class="bold"><i class="emphasis">command(s)</i></b>$ <b class="bold">ENDIF</b> | % <b class="bold">if (<span class="emphasis"><iexpression</i></span>) then</b><b class="bold"> </b><b class="bold">else</b><b class="bold"> </b><b class="bold">endif</b> |
| Form: | $ <b class="bold">IF</b> <b class="bold"><i class="emphasis">expression</i></b> <b class="bold">THEN</b> <b class="bold"><i class="emphasis">command</i></b> | |
| Example: | $ <b class="bold">TYPE TEST.COM</b>$! Report a file's executable status$ INQUIRE A "Enter filename:"$ IF (F$PARSE(A,,,"TYPE") .EQS. ".EXE")$ THEN$ WRITE SYS$OUTPUT A," is-executable"$ ELSE$ WRITE SYS$OUTPUT -A," is not-executable"$ ENDIF | % <b class="bold">cat test_script</b># Report a file's executable statusecho -n "Enter filename:"set a= $ |
| Example: | $ <b class="bold">TYPE TEST.COM</b>$! Display a non-empty file$ IF (F$FILE_ATTRIBUTES-(P1, "EOF") .EQ. 0) THEN GOTO EMPTY$ TYPE/PAGE 'P1'$ EXIT$ EMPTY:... |
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