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**********NB -i have read previous posts that look like duplicates but I cannot get this to work, Id really appreciate an explicit answer ********** I know this is a duplicate but I have read the previous posts and I still cant get this to work. sorry.

I'm working in bash trying to match a pattern that is stored in a variable using awk

In this example the string I want to match is xxx and I am storing it in the variable pattern. Imagine in the file $file there is a line that reads xxx yyy

Then if I enter the pattern string explicitly

awk '/xxx/{print $0}' $file

the output is xxx yyy (which is what I want, its printed out the line containing xxx)

but if I pass the pattern to be matched via a variable then there is no match

pattern="xxx"
awk -v pat="$pattern" '/pat/{print $0}' $file

no output

I checked the variable was getting passed to awk with

awk -v pat="$pattern" 'BEGIN {print pat}'

output: xxx as I was hoping.

Sorry, I guess this is easy but I'd really appreciate an answer. thanks

user3111174
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  • Use `$0 ~ pat` rather than `/pat/` as explained here [Pass shell variable as a /pattern/ to awk](https://unix.stackexchange.com/questions/120788/pass-shell-variable-as-a-pattern-to-awk) – steeldriver Feb 07 '19 at 19:02
  • thanks. that works but would you mind briefly explaining why – user3111174 Feb 07 '19 at 19:11
  • I'm not sure I can explain it - except that's what the language design requires (i.e. if `/pat/` was allowed to mean "match the contents of variable `pat`", then it would no longer be possible to match the regular expression `p` `a` `t` - whereas `$0 ~ pat` versus `$0 ~ "pat"` is unambiguous) – steeldriver Feb 07 '19 at 19:48

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