Bash script replace two fields in a text file using variables

Question

This should be a simple fix but I cannot wrap my head around it at the moment.

I have a comma-delimited file called my_course that contains a list of courses with some information about them.

I need to get user input about the last two fields and change them accordingly.

Each field is constructed like: CourseNumber,CourseTitle,CreditHours,Status,Grade

Example file:

CSC3210,COMPUTER ORG & PROGRAMMING,3,0,N/A
CSC2010,INTRO TO COMPUTER SCIENCE,3,0,N/A
CSC1010,COMPUTERS & APPLICATIONS,3,0,N/A

I get the user input for 3 things: Course Number, Status (0 or 1), and Grade (A,B,C,N/A)

So far I have tried matching the line containing the course number and changing the last two fields. I haven't been about to figure out how to modify the last two fields using sed so I'm using this horrible jumble of awk and sed:

temporary=$(awk -v status=$status -v grade=$grade '
BEGIN { FS="," }; $(NF)=""; $(NF-1)="";
/'$cNum'/ {printf $0","status","grade;}'  my_course)

sed -i "s/CSC$cNum.*/$temporary/g" my_course

The issue that I'm running into here is the number of fields in the course title can range from 1 to 4 so I can't just easily print the first n fields. I've tried removing the last two fields and appending the new values for status and grade but that isn't working for me.

Note: I have already done checks to ensure that the user inputs valid data.

Fredrik Pihl · Accepted Answer · 2013-03-27 15:09:15Z

1

Use a simple awk-script:

BEGIN {
  FS=","
  OFS=FS
}

$0 ~ course {
  $(NF-1)=status
  $NF=grade
} {print}

and on the cmd-line, set three parameters for the various parameters like course, status and grade.

in action:

$ cat input
CSC3210,COMPUTER ORG & PROGRAMMING,3,0,N/A
CSC2010,INTRO TO COMPUTER SCIENCE,3,0,N/A
CSC1010,COMPUTERS & APPLICATIONS,3,0,N/A

$ awk -vcourse="CSC3210" -vstatus="1" -vgrade="A" -f grades.awk input
CSC3210,COMPUTER ORG & PROGRAMMING,3,1,A
CSC2010,INTRO TO COMPUTER SCIENCE,3,0,N/A
CSC1010,COMPUTERS & APPLICATIONS,3,0,N/A

$ awk -vcourse="CSC1010" -vstatus="1" -vgrade="B" -f grades.awk input
CSC3210,COMPUTER ORG & PROGRAMMING,3,0,N/A
CSC2010,INTRO TO COMPUTER SCIENCE,3,0,N/A
CSC1010,COMPUTERS & APPLICATIONS,3,1,B

edited Mar 27, 2013 at 15:09

answered Mar 27, 2013 at 10:14

Fredrik Pihl

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1 Comment

Ed Morton Over a year ago

+1 for the answer but don't use all-upper-case for your variable names - that's for builtin variables like NR, OFS, FILENAME, etc.

aragaer · Accepted Answer · 2013-03-27 06:14:36Z

0

It doesn't matter how much commas you have in course name as long as you look only at last two commas: sed -i "/CSC$cNum/ s/.,[^,]*$$/$status,$grade/" The trick is to use $ in pattern to match the end of line. $$ because of double quotes.

And don't bother building the "temporary" line - apply substitution only to line that matches course number.

answered Mar 27, 2013 at 6:14

aragaer

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