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awk search syntax

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# 1  
Old 01-21-2020
awk search syntax
I need help with understanding awk search feature.


Here I am trying to search by 4th field in this file:


Code:
$ cat xx
471013,A20,asd,100,FEATURE UNKNOWN
171014,A22,sdf,101,FEATURE WITH SUB-ELEMENT
172822,20X,xcv,102,SUB-ELEMENT
101102,22X,asd,103,CODED

When I try the search feature I get nothing:
Code:
$ awk -F, '/$4 ~ "101"/{print}' xx        

$

When I just use IF statement it works as expected:
Code:
$ awk -F, '{ if($4 == 101)print; }' xx
171014,A22,sdf,101,FEATURE WITH SUB-ELEMENT
$

Please help me understand what do I do wrong in using the search // syntax
Thanks
# 2  
Old 01-21-2020
Hi
This way you won't succeed too
Code:
awk -F, '{ if(/$4 ~ "101"/)print; }' xx

# 3  
Old 01-21-2020
In awk, /.../ is (sort of) a regex constant. man awk:
Quote:
3. Regular expressions
In the AWK language, records, fields and strings are often tested for matching a regular expression. Regular expressions are enclosed in slashes, and

expr ~ /r/

is an AWK expression that evaluates to 1 if expr "matches" r, which means a substring of expr is in the set of strings defined by r. With no match the expression evaluates to 0; replacing ~ with the "not match" operator, !~ , reverses the meaning. As pattern-action pairs,

/r/ { action } and $0 ~ /r/ { action }

are the same, and for each input record that matches r, action is executed. In fact, /r/ is an AWK expression that is equivalent to ($0 ~ /r/) anywhere except ...
So, your expression /$4 ~ "101"/ will try to match exactly this string : $4 ~ "101" - which it won't find in your sample file.
Try
Code:
awk -F, '$4 ~ /101/' xx

which might do exactly what you targeted for.
These 2 Users Gave Thanks to RudiC For This Post:
migurus nezabudka
# 4  
Old 01-21-2020
Thank you RudiC
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