Novice. bash for i in $1 construct

bkelly · 08-30-2018, 04:25 PM

Linux novice
In a bash script is found:

Code:

getInputFiles () {
for i in $1
do
   if [ ! -e "$i" ]
   then
     continue
   fi
...
done

All calls to this function use command line arguments for the function arguments, but nothing says what those arguments should be.
I see the -e and $1 meaning: If it is not true that the file named $1 exists then ...
But then, that for i in a file name does not make sense to me.
Do the double quotes around the $1 make things different?
My searches have not been fruitful.
Where can I find a web page that describes this.

Edit: I have extracted the function into a test script trying to get the do loop to cycle. I used an directory name (containing several files), a file, and a quoted pair of files to no avail.

Edit 2:
I really should have put the whole thing in here. But I cannot copy and paste and a bit of dyslexia makes re-typing a bit of a problem. But here it is and please try to be tolerant of typos.

Code:

getInputFiles () {
   sortfiles=""
   echo "args are $@"
   for i in $1
   do
      if [ ! -e "$i" ]
      then
         echo "first if taken"
         continue
      fi

      echo "finished section 1"
      if [ ! -r "$i" ]
      then
         echo 1>&2 "$i file is not readable"
         exit 1
      fi

      echo "finished section 1"
      if [ ! -s "$i" ]
      then
         echo 1>&2 "$i is empty"
         exit 1
      fi

   sortfiles="$sortfiles $2 \"$i\""
  done
  echo $sortfiles
  echo "exiting function"
}

EDIT 3: Added diagnostic echos.

lougavulin · 08-30-2018, 05:01 PM

It is just a guess.

But :

Code:

if [ ! -e "$1" ]

Should be :

Code:

if [ ! -e "$i" ]

And so, you call it :

Code:

getInputFiles "blah bloh bluh"

It will not do what is in '...' if blah, bloh and bluh files does not exist.

Otherwise I'm skeptical as you are.

bkelly · 08-30-2018, 05:34 PM

In post 2 you are correct, that was a typo on my part. I have corrected and checking my test file.

NevemTeve · 08-31-2018, 06:19 AM

Maybe it is meant to be called like this:

Code:

./myscript "input1.txt input2.txt input3.txt" "output.txt"

or:

Code:

./myscript "$(echo input*.txt)" "output.txt"

lougavulin · 08-31-2018, 06:30 AM

Quote:

Originally Posted by NevemTeve

Maybe it is meant to be called like this:

Code:

./myscript "input1.txt input2.txt input3.txt" "output.txt"

or:

Code:

./myscript "$(echo input*.txt)" "output.txt"

I think so.

The purpose is to get a list of input files that exist, are readable and not empty.

The first argument is the list of file to check.
The second seems to be a current list of files which have already been checked.

bkelly · 08-31-2018, 09:54 AM

I request primary focus on these two points first please.
How should I read that for statement?. The behavior appears to expect a list of files.
And what is the purpose of the 1>&2 in the statement
echo 1>&2 "$i some text"

And now for additional complexity.

The function is called later in the script and looks like this:

Code:

ftmatspresortlist=`getInputFiles "$TMATS_PRE_SORTED" ""`

The single quotes are from the top left key to the left the number one key, not the standard that is shared with double quotes. When that line is added to the script to call the function then most of the echos in the function are suppressed. Including the first echo before the for loop. (see the edits in the OP that added a few echos.) When the calling function is changed to:

Code:

getInputFile "$TMATS_PRE_SORTED"

All the echoes work again.
I am confused.

Edit 1:
Even more confused. When using the more simple function call, and just putting a variable to capture the return value, that causes all the echos in the function to no longer echo to the screen. That seems reasonable. Maybe it will echo to the return value.
Except
The variable to catch the return value is unchanged.

Code:

ftmatspresortlist="default"
ftmatspresortlist=getInputFiles "$TMATS_PRE_SORTED"
echo "ftmatspresortlist = $ftmatspresortlist"

and "default" is output.

Please bear in mind that I am a Linux and Bash novice.

Edit
there is something funky that might be related. I have posted that question here:
https://www.linuxquestions.org/quest...15#post5898415

NevemTeve · 08-31-2018, 11:14 AM

Q: What does echo "text" >&2 or echo "text" 1>&2 do?
A: It writes the messages to the standard error.

Q: How to get the output of a command into a variable?
A: Use the $() syntax:

Code:

Var1="$(cat somefile)"
Var2="$(echo *)"
Var3="$(getInputFiles "$TMATS_PRE_SORTED")"

Bonus:
Q: How can I test the problematic for statement in my terminal? I don't have such $1 when using a shell in terminal.
A: You can assign values to $1 $2 etc with set command:

Code:

set 'some words in the first parameter' 'other words in the second'
for i in $1; do echo "$i"; done
some
words
in
the
first
parameter