Testing if a String exists inside an Array of Strings

Question

I am writing a script that compares the first 3 letters of every line (by using cut to get them) in a file to strings inside an Array. I have already looked around but the solutions i found didn't work on my system.

Right now It looks like this:

weekdays=([Mon]=1 [Tue]=1 [Wed]=1 [Thu]=1 [Fri]=1 [Sat]=1 [Sun]=1) input="/Foo/Bar.log" while read -r line do cutline="$(echo ${line} | cut -c 1-3" if [[ ${weekdays["$cutline"]} ]] then echo "Match" else echo "No Match" fi done < ${input} 

The Line gets cut properly but something during the test returns a false Positive since no matter what the first 3 Letters are it returns a "Match".

When I checked the script with -x it showed me, instead of the actual test that it instead used

[[ -n 1 ]] 

And when I tested it with the [ ] expresion it showed a 1

Does it check for every single char in the array and not just the whole words, or is there something else wrong with it?

If there is no problem, is there another way to compare the first 3 letters of a line to everything insde an array before continuing with the next?

As a side note: I am indeed running Bash 4, so associative arrays should work

Answer 1

The basic error is that you aren't actually declaring an associative array:

$ weekdays=(["Mon"]=1 ["Tue"]=1 ["Wed"]=1 ["Thu"]=1 ["Fri"]=1 ["Sat"]=1 ["Sun"]=1) $ echo ${weekdays[@]} 1 $ echo ${weekdays[0]} 1 $ echo ${weekdays[2]} $ 

I'm not entirely sure how bash is dealing with it and why it just takes a 1, but I am sure that that is not an associative array. As explained in man bash (emphasis mine):

An indexed array is created automatically if any variable is assigned to using the syntax name[subscript]=value. The subscript is treated as an arithmetic expression that must evaluate to a number. To explicitly declare an indexed array, use declare -a name (see SHELL BUILTIN COM‐ MANDS below). declare -a name[subscript] is also accepted; the sub‐ script is ignored.

Associative arrays are created using declare -A name.

So, try this instead and it will work as you expect:

declare -A weekdays=(["Mon"]=1 ["Tue"]=1 ["Wed"]=1 ["Thu"]=1 ["Fri"]=1 ["Sat"]=1 ["Sun"]=1) 

---

That said, your script is a bit more complex than you need. Here's a simpler version using the same approach:

#!/bin/bash declare -A weekdays=(["Mon"]=1 ["Tue"]=1 ["Wed"]=1 ["Thu"]=1 ["Fri"]=1 ["Sat"]=1 ["Sun"]=1) input="/Foo/Bar.log" cut -c 1-3 "$input" | while read -r line; do if [[ ${weekdays["$line"]} ]] then echo "Match : $cutline : ${weekdays[$line]}" else echo "No Match" fi done 

Although I would probably do it like this:

#!/bin/bash cut -c 1-3 "$1" | while read -r line; do case $line in "Mon"|"Tue"|"Wed"|"Thu"|"Fri"|"Sat"|"Sun") echo yes;; *) echo no;; esac done 

Then, run the script with the target file name as an argument:

script.sh /Foo/Bar.log" 

Answer 2

I'd use one invocation of a text-processing tool to process text, not several tools for each line of input:

awk -v 'weekday=(Mon|Tue|Wed|Thu|Fri|Sat|Sun)' ' {print ($0 ~ "^" weekday ? "" : "No ") "Match"}' < "$input" 

You'd use a loop if you needed to run a particular application for each line of the input, but if it's just text processing like outputting the line to some file, then awk can do it like:

awk -v 'weekday=Mon|Tue|Wed|Thu|Fri|Sat|Sun' ' (day = substr($0, 1, 3)) ~ weekday { print substr($0, 4) > day ".txt" } < "$input"