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system command within awk

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# 1  
Old 04-08-2009
system command within awk
I was trying commands within awk. i got stuck here. i take 2 files.

Code:
cat input

first
second
third
fourth
fifth
sixth
seventh
eighth
ninht
tenth

Code:
cat add

***************
Nirbhay
***************

i run the command
Code:
awk '{ if ( NR == 5 ) { print system("cat add") "\n" $0 } else { print } }' input > output

cat output

first
second
third
fourth
***************
Nirbhay
***************
0
fifth
sixth
seventh
eighth
ninht
tenth

My query is that why does 0 appears in the output file, though it is neither in input, nor in add. & what can i do to get rid of it ?
# 2  
Old 04-08-2009
Hi Nirbhay
I think this "0" is the return from the system("cat add") command.

Try this:
awk '{ if ( NR == 5 ) { print system("cat add") 1>/dev/null } else { print }}' input

redirecting return code from system command to null.

Hope this helps.
# 3  
Old 04-08-2009
yes Angad, you're right. But then, using 1>/dev/null inside awk causes a few problems as i can see

Code:
awk '{ if ( NR == 5 ) { print system("cat add") 1>/dev/null "\n" $0 } else { print } }' input > output

this simply ignores everything else in the action. here "\n" $0 are ignored. Rest of the line is not printed.

Code:
awk '{ if ( NR == 5 ) { print (system("cat add") 1>/dev/null) "\n" $0 } else { print } }' input > output

enclosing in braces gives another problem. i get 1 in the output
Code:
first
second
third
fourth
***************
Nirbhay
***************
1
fifth
sixth
seventh
eighth
ninht
tenth

# 4  
Old 04-08-2009
no need to call system to invoke cat. do everything with awk.
Code:
# awk 'NR==5{while (( getline line <"add") > 0 ) {print line}}NR!=5' file
first
second
third
fourth
***************
Nirbhay
***************
sixth
seventh
eighth
ninht
tenth

or
Code:
# awk 'FNR==NR{a[++d]=$0;next}FNR==5{for(i in a)print a[i]}FNR!=5' add file
first
second
third
fourth
***************
Nirbhay
***************
sixth
seventh
eighth
ninht
tenth

# 5  
Old 04-08-2009
Or simply with sed:

Code:
sed '4r add' input

Regards
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