05-03-2017
Hi, in this case this is not awk but shell syntax (the awk script is inside the single quotes) and it creates what is called a "pipeline".
Quote:
A pipeline is a sequence of one or more commands separated by the control operator '|'. For each command but the last, the shell shall connect the standard output of the command to the standard input of the next command as if by creating a pipe and passing the write end of the pipe as the standard output of the command and the read end of the pipe as the standard input of the next command.
Shell Command Language
So the standard output of the
awk command becomes standard input for the
psxy command..
This User Gave Thanks to Scrutinizer For This Post:
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POPEN(3) Library Functions Manual POPEN(3)
NAME
popen, pclose - initiate I/O to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(command, type)
char *command, *type;
pclose(stream)
FILE *stream;
DESCRIPTION
The arguments to popen are pointers to null-terminated strings containing respectively a shell command line and an I/O mode, either "r" for
reading or "w" for writing. It creates a pipe between the calling process and the command to be executed. The value returned is a stream
pointer that can be used (as appropriate) to write to the standard input of the command or read from its standard output.
A stream opened by popen should be closed by pclose, which waits for the associated process to terminate and returns the exit status of the
command.
Because open files are shared, a type "r" command may be used as an input filter, and a type "w" as an output filter.
SEE ALSO
pipe(2), fopen(3S), fclose(3S), system(3), wait(2), sh(1)
DIAGNOSTICS
Popen returns a null pointer if files or processes cannot be created, or the shell cannot be accessed.
Pclose returns -1 if stream is not associated with a `popened' command.
BUGS
Buffered reading before opening an input filter may leave the standard input of that filter mispositioned. Similar problems with an output
filter may be forestalled by careful buffer flushing, for instance, with fflush, see fclose(3S).
Popen always calls sh, never calls csh.
7th Edition May 15, 1985 POPEN(3)