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Variable filtering in awk

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# 1  
Old 08-20-2013
Variable filtering in awk

Hello all,
can you explain why this filter does not work, it prints all the lines in the file:
awk -v sel="TestString" 'sel'  file

while these work:
awk '/TestString/' file
awk -v sel="TestString" '$0~sel'  file

# 2  
Old 08-20-2013
awk -v sel="TestString" '$0~sel'  file

is telling awk to filter - to do something!
# 3  
Old 08-20-2013
In other words, my question is about how to write an awk statement that will use the variable and use it in the form of a statement like:
awk -v var="TestString" '/ var /' file

to achieve filtering.
Any suggestions?
# 4  
Old 08-20-2013
Below awk prints all as its default action is to print everything if "sel" is true (not null or non-zero)...
awk -v sel="TestString" 'sel'  file

The awk listed below prints nothing as "sel" is false (null or zero)...
awk -v sel="" 'sel'  file

# 5  
Old 08-20-2013
Just curious:
Is there anyway to get something 'like' this to work, where the var is used for the / / construct ?
awk -v var="TestString" '/ var /' file

Any suggestion is appreciated.
# 6  
Old 08-20-2013
awk -v var="TestString" '$0~var' file

# 7  
Old 08-20-2013
/.../ is a regex constant; /var/ tests input lines for occurrence of a literal string "var". To match variables, you need to do as joeyg and Jotne suggest.
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