CODEWITHSUNDEEP
awk
Ghost
Ghost

Reputation: 1523

Compare (match) command output with lines in file

I'm piping the output of a command to awk and i want to check if that output has a match in the lines of a file.

Let's say i have the following file:

aaa
bbb
ccc
...etc

Then, let's say i have a command 'anything' that returns, my goal is to pipe anything | awk to check if the output of that command has a match inside the file (if it doesn't, i would like to append it to the file, but that's not difficult..). My problem is that i don't know how to read from both the command output and the file at the same time.

Any advice is welcome

Upvotes: 0

Views: 74

Answers (2)

jas
jas

Reputation: 10865

My problem is that i don't know how to read from both the command output and the file at the same time.

Use - to represent standard input in the list of files for awk to read:

$ cat file
aaa
bbb
ccc

$ echo xyz | awk '{print}' - file
xyz
aaa
bbb
ccc

EDIT

There are various options for handing each input source separately:

Using FILENAME:

$ echo xyz | awk 'FILENAME=="-" {print "Command output: " $0} FILENAME=="input.txt" {print "from file: " $0}' - input.txt
Command output: xyz
from file: aaa
from file: bbb
from file: ccc

Using ARGIND (gawk only):

$ echo xyz | awk 'ARGIND==1 {print "Command output: " $0} ARGIND==2 {print "from file: " $0}' - input.txt
Command output: xyz
from file: aaa
from file: bbb
from file: ccc

When there are only two files, it is common to see the NR==FNR idiom. See subheading "Two-file processing" here: http://backreference.org/2010/02/10/idiomatic-awk/

$ echo xyz | awk 'FNR==NR {print "Command output: " $0; next} {print "from file: " $0}' - input.txt
Command output: xyz
from file: aaa
from file: bbb
from file: ccc

Upvotes: 1

Ed Morton
Ed Morton

Reputation: 203229

command | awk 'script' file -

The - represents stdin. Swap the order of the arguments if appropriate. Read Effective Awk Programming, 4th Edition, by Arnold Robbins to learn how to use awk.

Upvotes: 0

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