Sort output of awk except for first line?

Question

This is a use case I am continually running into in parsing CSV files. When it is an inline awk script embedded in a shell script, I can use this workaround:

myfile="$(mktemp)"
awk '(awk script here)' > "$myfile"
head -1 "$myfile"
sed 1d "$myfile" | sort
rm "$myfile"

(Or using appropriate mktemp template for BSD mktemp; GNU works as above.)

However, when writing a full fledged awk script with a shebang #!/bin/awk -f, I don't want to have to change it to a shell script just to handle this one factor of sorting the output.

How can I do this in awk? Or, if there is no native sort function in awk, where can I learn about awk pipelines and how can I use pipelines to accomplish this without changing the shebang?

For what it's worth, when I am creating CSV files, I always echo the headers to the final filename right off the bat. Then I do all of my sorting in the temporary file, and when I'm done, cat tmpfile >> final.csv; rm tmpfile. — rubynorails
– rubynorails, Commented Nov 17, 2015 at 4:09
Good to know, but I want to do this with a pure awk script. In cases where the header is going to be parsed and changed in awk and change the behavior of the awk script (for example, allowing your input columns in arbitrary sequence as long as the headers match pre-defined values in some sequence, and then always outputting a specific column sequence), you need to handle both the header and the content within the same awk script. Thus my question. (That is just one example use case; there are others.) — Wildcard
– Wildcard, Commented Nov 17, 2015 at 4:14
Depending on what you want to do with your output, send the headings to stderr could be an option. — muru
– muru, Commented Nov 17, 2015 at 4:15
Note that gawk provides two array sorting functions: asort to sort by value, and asorti to sort by index. — PM 2Ring
– PM 2Ring, Commented Nov 17, 2015 at 6:15

John1024 · Accepted Answer · 2015-11-17 05:21:20Z

7

Here is an example that sorts all lines but the first:

#!/bin/awk -f
BEGIN{cmd="sort"}
NR==1{print;next}
{print $1,$2 | cmd}
END{close(cmd)}

Example

Consider this file:

$ cat file
Letter  Value
A       12
D       10
C       15
B       13

Then:

$ awk -f script.awk file
Letter  Value
A 12
B 13
C 15
D 10

The first input line is the first output line. The remaining lines are sorted.

edited Nov 17, 2015 at 5:21

answered Nov 17, 2015 at 4:12

John1024

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