Read a file line by line, shell script

dabigmooish · #1 05-Sep-2007, 06:18

I've got a file that is of variable length, it will always have a minimum of two lines but no maximum. The first line contains either ON or OFF. The rest of the lines are numbered and contain the Month Day Time. The file looks like this:

Code:

ON
1 09 04 1030
2 09 04 1100
3 09 04 2315
4 09 05 0700
...

I'm trying to write some code that will remove the second line of the file and renumber the others. Here is what I had:

Code:

overwrite() {

# Variable is a counter used for special situations where all entries #
#  in the on_off file are deleted on run. Without this variable no new#
#  entries will be written                                                         #
RUN=`expr $RUN + 1`
    
echo "ON" >> $ON_OFF_FILE.$RUN

# Loop that Creates the temp file
while [ $TEMP2 -lt $TLINES ] || [ $TEMP2 -eq $TLINES ]
do
         
     LINETOWRITE=`grep "$TEMP2 " $ON_OFF_FILE | awk '{print $2,$3,$4}' `
     echo "`expr $TEMP2 - 1` $LINETOWRITE" >> $ON_OFF_FILE.$RUN
     TEMP2=`expr $TEMP2 + 1`
     
done
     
mv $ON_OFF_FILE.$RUN $ON_OFF_FILE     

}

This works fine as long as the date isn't the smaller then the number of entries in the file. When it is, it causes issues. I was thinking of using the cut command with a "/n" delineator but I can't get that to work. Does anyone have any suggestions as to how to do this?

davekw7x · #2 05-Sep-2007, 08:49

Quote:

Originally Posted by dabigmooish

I'm trying to write some code that will remove the second line of the file and renumber the others.

Are you always going to write "ON" as the first line of the output file, as your code seems to indicate?

Since you don't indicate any kind of error checking, couldn't you just use something like the following:

Code:

#!/bin/bash
#
# Replace the first line of the file with "ON"
# Skip the second line
# Renumber the first field of the remaining lines
#
INPUTFILE=test.txt
OUTPUTFILE=modified.txt
echo "ON" > $OUTPUTFILE
awk '(NR > 2) {$1=$1-1; print}' $INPUTFILE >> $OUTPUTFILE

(This is just to show how simple the awk stuff can be. Whatever you did to get the input file and output file names is still up to you.)

File test.txt:

Code:

OFF
1 09 04 1030
2 09 04 1100
3 09 04 2315
4 09 05 0700

File ]kbd]modified.txt[/kbd] after running the above script

Code:

ON
1 09 04 1100
2 09 04 2315
3 09 05 0700

On the other hand, If, as you described it, you want to reproduce the first line exactly as it appeared, and then skip the second line and renumber the rest, then the awk part could look like:

Code:

#!/bin/bash
#
# Reproduce the first line
# Skip the second line
# Renumber the first field of the remaining lines
#
INPUTFILE=test.txt
OUTPUTFILE=modified.txt
awk '(NR == 1){print} (NR > 2) {$1=$1-1; print}' $INPUTFILE > $OUTPUTFILE

File modified.txt after this one:

Code:

OFF
1 09 04 1100
2 09 04 2315
3 09 05 0700

If this doesn't meet your needs, then maybe you could give a complete program specification.

Regards,

Dave

dabigmooish · #3 05-Sep-2007, 09:41

Thanks this is what I need. I think I'm still stuck thinking approaching shell programming as if it were C++. I've never seen awk used like that and it never occured to me to try that. Anyway to answer your questions, Yes I will always put ON as the first line, if it's OFF the script won't run anyway. All the error checking is elsewhere. This is but one function of many. Thanks for your help dave.

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Read a file line by line, shell script

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Re: Read a file line by line, shell script