I explained the reasons why the awk code you supplied won't work. You can choose to ignore my comments and continue to wonder why your code doesn't work. Trying to use shell variables in awk and assume that shell variable expansions will work in awk will never work the way you have used them because awk is not bash.
Uh, my awk code works fine provided $input is a file in the working directory. I am not using any special editors, and after reading RudiC's comments, I restarted my system and went to a real terminal (not terminal emulator) and did the following at a prompt:
AfileinDir is simply a file with some data in a couple of fields.
code works fine. Go to a directory on your computer, define input as a file in that directory that has at least 2 fields and copy paste the awk line above.
My first question relates to the else portion of the code which I haven't included. I know * that * part doesn't work, which is why I asked for help on improving the script.
My second question is still not being answered because so far the respondents are saying my code doesn't work when it does?? No special emulators. Straight from tty1 terminal.
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Uh, my awk code works fine provided $input is a file in the working directory. I am not using any special editors, and after reading RudiC's comments, I restarted my system and went to a real terminal (not terminal emulator) and did the following at a prompt:
AfileinDir is simply a file with some data in a couple of fields.
code works fine. Go to a directory on your computer, define input as a file in that directory that has at least 2 fields and copy paste the awk line above.
My first question relates to the else portion of the code which I haven't included. I know * that * part doesn't work, which is why I asked for help on improving the script.
My second question is still not being answered because so far the respondents are saying my code doesn't work when it does?? No special emulators. Straight from tty1 terminal.
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Please explain in English what you think the expression in the if statement in:
is doing. Since you can't get the else clause to work, by definition, your code is not working. How can you say your code is working when it won't run if the filename you pass to it is not a file that exists in the current directory? Furthermore, it is my belief that what the code above is doing is not doing what you think it is. Whether or not that means it is working when the named file does exist is open for discussion. I claim that if it is not doing what you think it is doing, it is not working. You claim that since the then clause of your if statement is working, everything is fine.
Without running the following code, what output do you think it would produce:
After you have decided what output you think it should produce, run it and compare the output you get to the output you thought it should produce. Then go back and look at how I said that expression in the if statement would be evaluated in my comments in post #4 in this thread.
Please run the above test and let us know what happens!
As I said before, I can't test your code using the version of awk that I have available on my system because the code you're using is not technically correct (and produces a syntax error in the version of awk that I'm using, but runs without producing a syntax error in the version of awk that you're using). I can force the version of awk I'm using to get the results you're seeing by changing your code to:
Please explain in English what you think the expression in the if statement in:
is doing. Since you can't get the else clause to work, by definition, your code is not working. How can you say your code is working when it won't run if the filename you pass to it is not a file that exists in the current directory? Furthermore, it is my belief that what the code above is doing is not doing what you think it is. Whether or not that means it is working when the named file does exist is open for discussion. I claim that if it is not doing what you think it is doing, it is not working. You claim that since the then clause of your if statement is working, everything is fine.
Never said the else clause was working, that's why I asked for a different way to script it.
First, the code will return an error, since the code you provided doesn't close the awk command nor does it provide it a file to look at.
But if those were present, and in English:
awk will first examine the file to see if it's present. Then it will evaluate the value of variable input to see if it is equal to the value of what a list (ls) command returns. ‘ls' will return every non hidden file in the directory it's run in, so strictly speaking, all the strings returned taken as a whole will not equal the value of input - but this is done in the context of an awk command with a specific file (the value of input) to look at, and if true (the file is present) it will print out the first field, followed by a tab, followed by the second field.
If, however, the value of input is not in the directory (the file isn't listed), then awk will exit with an error. That error is
where ‘a' is not a file in the directory. This is the reason why else is never executed - because the error is returned before the condition and commands that form part of the if statement are ever read.
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Quote:
Originally Posted by Don Cragun
Without running the following code, what output do you think it would produce:
After you have decided what output you think it should produce, run it and compare the output you get to the output you thought it should produce. Then go back and look at how I said that expression in the if statement would be evaluated in my comments in post #4 in this thread.
Please run the above test and let us know what happens!
it will return a prompt because you didn't close off the awk command before providing the file
with the awk command closed off,
Sorry, I had to run it to see what the code was doing . But you're changing the value of both $input and $(ls) so it's going to list the values of those as you specified.I don't see how this helps me with either of my questions in the original post.
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Quote:
Originally Posted by Don Cragun
As I said before, I can't test your code using the version of awk that I have available on my system because the code you're using is not technically correct (and produces a syntax error in the version of awk that I'm using, but runs without producing a syntax error in the version of awk that you're using). I can force the version of awk I'm using to get the results you're seeing by changing your code to:
I sincerely apologize for not being able to test the code I suggested you try on the system I'm using (and, therefore, missing a closing single-quote in the code I provided).
I'm sorry that you believe that I should be required to download all of the software you're using on your system onto my system in order to try to help you understand the code you're using. I AM NOT GOING TO DO THAT! I am perfectly happy with the way awk works on my system even though awk on your system has some (non-standard) extensions that do some nice things in some cases. What those extensions do has nothing to do with what you're doing nor with what you're trying to do. The difference we are seeing is because you are doing something that the standards describe as producing "unspecified behavior" and your version of awk produces a different unspecified behavior than my version of awk produces.
All that I was trying to do with the awk statement I was trying to get you to run was to show that the value of $input and the value of $(ls) inside your awk script have absolutely no relationship to the value of $input or the value of $(ls) in bash outside of your awk script.
Nothing in your explanation in English of what the expression in your awkif statement is true. The awk variable input is not defined anywhere in your awk code (only the shell variable input is defined; not the awk variable input). In bash$(ls) is a command substitution that runs the ls command and substitutes the output it produces. In awk$(ls) is a command that expands to the contents of the field number specified by the value of the awkls variable converted to an integer. The awk and shell == operators are a request to compare the two operands on both sides of that operator. If there is more than one file in a directory and one of those files is the name of the file you're processing, there is absolutely no way that the name of that one file can possibly be equal to the list of names of files that are present in that directory. Since you are seeing the output you're seeing, your version of awk has to be expanding both sides of the comparison to the expansion of $0 which (in awk) is the entire contents of the current input line.
With the missing quote added AND assuming that you had already defined the shell variable input as you had shown before AND assuming that the file named AfileinDir contained the two input lines:
I would expect the sequence of commands:
to produce output very similar to the following:
Despite what you said, absolutely nothing in the code above assigns any value to the awk variables input and ls; that code only displays the values that the expression in your awkif statement expression are comparing (i.e., the entire contents of the current line in AfileinDir on both sides of the ==).
Maybe if we rewrite that as:
which (if you set the contents of the file named AfileinDir to the contents I specified above), I expect will produce the output:
you will see that $input and $(ls) in your awk script do not expand to the strings you think they will expand to.
I know that you don't want to just use the shell (i.e. bash) to determine whether or not the variable read from your script's user (i.e. input) is the name of a file in your current directory, but that is exactly what the simple bash command:
that I suggested in post #4 did for you. If the shell variable input contains the name of a regular file that exists in the current directory, it will perform the while loop in the then clause of the if statement. Otherwise, it will print the name of the file the user supplied and say that that file is not in this Directory and then exit with a non-zero exit status as specified in the else clause of the if statement.
This User Gave Thanks to Don Cragun For This Post:
Uh, my awk code works fine provided $input is a file in the working directory. ...
Quote:
Never said the else clause was working,
I'm not as eloquent in the English language as Don Cragun is, nor am I as patient. And, I hope you believe me really wanting to help you.
That said: He's right, and you are wrong.
Your code does NOT "work fine". It may by sheer accident provide an answer that suits you, but I'm sure that's not what you want.
For the if clause in question, replace it with
or, even better,
and see what you get, mayhap even trying the else clause. You may also want to closely read and understand all the posts in your thread.
Then come back, and we'll continue the discussion.
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