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awk's getline < "-" seems not work for pipe awk's getline < "-" seems not work for pipe
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Old 04-07-2009
qiulang qiulang is offline
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awk's getline < "-" seems not work for pipe
Hi all,

I have an gawk script to get user's input, So I use

getline name < "-" (or getline name < "/dev/stdin") in my script

They both work fine when my script deals with files. But it is broken for pipes.
When I try "some command | my awk script", the variable name just gets an empty value (""), it does not get the value from stdin at all.

Why is that ? And how do I fix it ?
Last edited by qiulang; 04-08-2009 at 08:01 AM..
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Old 04-08-2009
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vidyadhar85 vidyadhar85 is offline Forum Staff  
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as far as i know get line deals with following six varients
Code:
getline 
sets $0, NF, FNR, and NR. 
getline var 
sets var, FNR, and NR. 
getline < file 
sets $0, and NF. 
getline var < file 
sets var. 
command | getline 
sets $0, and NF. 
command | getline var 
sets var.
no where its mentioned that it take i/p from stdin
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Old 04-08-2009
qiulang qiulang is offline
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It mentions in gawk user's guide The GNU Awk User's Guide
(seach "-").

And it works for files processing. Just seems not work for pipe.
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Old 04-08-2009
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vidyadhar85 vidyadhar85 is offline Forum Staff  
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Quote:
Originally Posted by qiulang View Post
It mentions in gawk user's guide The GNU Awk User's Guide
(seach "-").

And it works for files processing. Just seems not work for pipe.
Buddy that means
if getline < "filename"
some command ' file2
now it getline read from filename
if getline < "-"
some command' file2
now it read from file2
it doesn't mean that it read from stdin
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Old 04-08-2009
qiulang qiulang is offline
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Quote:
Originally Posted by vidyadhar85 View Post
Buddy that means
if getline < "filename"
some command ' file2
now it getline read from filename
if getline < "-"
some command' file2
now it read from file2
it doesn't mean that it read from stdin
Hey just take a try getline name < "-" you will know it will work for file processing.

Actually "sed & awk" had several examples of getline < "-" to read user's input from stdin.

I just want to know how to make it work for pipe.
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Old 04-08-2009
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radoulov radoulov is online now Forum Staff  
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Did you try:

Code:
command | getline
See vidyadhar85's post above.
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Old 04-08-2009
Franklin52 Franklin52 is offline Forum Staff  
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Quote:
Originally Posted by qiulang View Post
Hey just take a try getline name < "-" you will know it will work for file processing.

Actually "sed & awk" had several examples of getline < "-" to read user's input from stdin.

I just want to know how to make it work for pipe.
You're right, getline < "-" gets the input from standard input.
What you can't do is to get input from a pipe and a file simultaneously. Get the users input in the BEGIN{} part.

Regards
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