Pfthb

I have a text file consisting of xyz coordinates, each defining a particular depth contour of a slope.
All of these lines are stored in one file, with each contour separated by ">"

The file looks like:

 >
 x1 y1 z1
 x2 y2 z2
 >
 x3 y3 z3
 ...

The file is huge and unwieldy and I want to print out the 7th point along each contour and pipe it into a tab delimited new file.

My code looks like this:

awk -v OFS='t' -v count=1 'if ($1 == ">") count/=count; else if (count%7 == 0) count+=1 print $0; else count+=1' infile > outfile

I keep getting an error message that says

 awk: syntax error at source line 1
 context is
 if ($1 == ">") count/=count; >>> else <<< if (count%7 == 0) count+=1; print $0; else count+=1
awk: illegal statement at source line 1

I've spent a while checking my syntax and bracketing and it seems ok, I just might be missing something with the variable reassignment?

Your syntax is very close; just a bit off. Looks like there may be some confusion between the curly braces and the normal parentheses. As you play around more with awk the difference should become much clearer.

Before I get to your particular syntax issue, note that a simpler approach can solve the same problem:

awk -v OFS='t' '$1 == ">" count = 1; next !(count++ % 7)' file

A multiline version your corrected code would be:

 if ($1 == ">") 
 count = 1
 
 else
 if (count % 7 == 0) 
 count += 1
 print $0
 
 else
 count += 1

As long as a statement is on its own line, you don't need a semicolon. But note that to make it a one-liner, you will need one as shown:

 if ($1 == ">") count = 1 else if (count % 7 == 0) count += 1; print $0 else count += 1