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Top Forums Shell Programming and Scripting Multiple variable substitution in a file in one go Post 302910469 by Don Cragun on Thursday 24th of July 2014 04:28:16 PM
Old 07-24-2014
Is this a homework assignment?

You haven't specified nearly enough to know what should be done here. And, some requirements could make this an extremely complex job requiring a full syntactic and semantic understanding of the shell you're using and of all of the commands invoked by your script.
  1. What delimits the start and end of the variable assignments to be removed and expanded by your script?
  2. Are occurrences of expansions of these variables to be replaced inside pairs of single quotes?
  3. Does your script need to be smart enough not to replace $ECHO in the command: $LS $ECHO_OLD?
  4. Does your script need to be smart enough to replace ${ECHO} as well as $ECHO?
  5. Is your script to search out and replace these variables in dotted and sourced files?
  6. What if a script creates an intermediate encoding that result in one of these variables being expanded as a side effect of running eval?
  7. What if a printf invocation leads to a string being put into a variable that will be expanded and run later in the script?

What have you tried? With what you have tried, what isn't working?
 

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exit(1)                                                            User Commands                                                           exit(1)

NAME
exit, return, goto - shell built-in functions to enable the execution of the shell to advance beyond its sequence of steps SYNOPSIS
sh exit [n] return [n] csh exit [ ( expr )] goto label ksh *exit [n] *return [n] DESCRIPTION
sh exit will cause the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an EOF will also cause the shell to exit.) return causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command exe- cuted. csh exit will cause the calling shell or shell script to exit, either with the value of the status variable or with the value specified by the expression expr. The goto built-in uses a specified label as a search string amongst commands. The shell rewinds its input as much as possible and searches for a line of the form label: possibly preceded by space or tab characters. Execution continues after the indicated line. It is an error to jump to a label that occurs between a while or for built-in command and its corresponding end. ksh exit will cause the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (See set below) turned on. return causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a '.' script, then it is the same as an exit. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
break(1), csh(1), ksh(1), sh(1), attributes(5) SunOS 5.10 15 Apr 1994 exit(1)
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