Please explain in English what you think the expression in the if statement in:
Code:
awk '{if($input == $(ls)) {print $1 "\t" $2;} }
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
Code:
awk: fatal: cannot open file `a' for reading (No such file or directory)
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 $(ls) so it's going to list the values of those as you specified.I don't see how this helps me with either of my questions in the original post.
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Quote:
Originally Posted by Don Cragun
As I said before, I can't test your code using the version of awk that I have available on my system because the code you're using is not technically correct (and produces a syntax error in the version of awk that I'm using, but runs without producing a syntax error in the version of awk that you're using). I can force the version of awk I'm using to get the results you're seeing by changing your code to:
Code:
awk '{if($input == $(ls+0)) {print $1 "\t" $2;} }
Code:
awk --version
GNU Awk 4.1.4, API: 1.1 (GNU MPFR 4.0.1, GNU MP 6.1.2)
Copyright (C) 1989, 1991-2016 Free Software Foundation.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
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. 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.