How to read multiple files from within awk script without passing at command line?

Question

I have an awk script which is called something like this:

awk -f d.awk /var/log/app*.log

And this works fine. Log file path is constant and not changing (only the number of files changes in this location due to log rotation) so I want to remove it from command line and hard code inside the awk script. Is there a way to skip passing this argument from command line and hard code it within the awk script and still achieve the same result?

I read about getline but it is not working for me. awk script outline is something like this:

BEGIN{
    #Initialization of few variable
}
match() {
    #Main process logic
    # Collect the output
    output=output" " result_after_processing
}
END{
    #Write the output to output file
    print output >> some_output_file
}

Why? Seems to me you want to work the other direction. Instead of awk -f, write a shell script which embeds the awk and uses /var/log/app*.log as arguments. — William Pursell
– William Pursell, Commented Jun 12, 2020 at 19:03
@WilliamPursell thanks for your reply. I thought of that but I need to call this awk from an existing C code and don't want to (or allowed to) add another layer in between. Problem is existing C code is very bad in parsing wild card (*) and producing some weird results. I don't have access to existing C code. Hence thought of getting rid of this argument. — RunSingh
– RunSingh, Commented Jun 12, 2020 at 19:06
The log file path is processed by the shell to give a list of filenames for awk to work on, you can't control that with awk — Inian
– Inian, Commented Jun 12, 2020 at 19:07
You can use getline < "filename" to read file a file, but it won't expand wildcards, and I don't think there's a way to reassign awk's input to another file in general. — Barmar
– Barmar, Commented Jun 12, 2020 at 19:10
@Inian, yes, you can, but it's ugly - you can populate awk's ARGC/ARGV based on your own scanning of a dir for files. — vgersh99
– vgersh99, Commented Jun 12, 2020 at 19:11

Ed Morton · Accepted Answer · 2020-06-12 20:05:38Z

5

BEGIN {
    cmd = "printf \047%s\n\047 /var/log/app*.log"
    while ( (cmd | getline line) > 0 ) {
        ARGV[ARGC++] = line
    }
    close(cmd)
}

should work as long as your file names don't contain newlines.

This is one of those rare cases where use of getline is appropriate - make sure to read http://awk.freeshell.org/AllAboutGetline if you're ever considering using it in future.

edited Jun 12, 2020 at 20:05

answered Jun 12, 2020 at 19:12

Ed Morton

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