Processing string in BASH and count the number of a substring beeing seen

Question

If there is a string:

[[some_str,another_str],[some_str,the_str],[some_str,the_str],[some_str,whatever_str]]

And I want output like this:

another_str: 1
the_str: 2
whatever_str:1

How could I do that?

score 4 · Answer 1 · edited Oct 31 '14 at 14:02

4

# read strings into an array, excluding [, ] and , characters
IFS='[],' read -r -a strings <<<'[[some_str,another_str],[some_str,the_str],[some_str,the_str],[some_str,whatever_str]]'

# store counts in an associative array
declare -A counts=()
for string in "${strings[@]}"; do
  [[ $string ]] || continue
  (( 'counts[$string]' += 1 ))
done

# iterate over that associative array and print counters
for string in "${!counts[@]}"; do
  echo "$string: ${counts[$string]}"
done

edited Oct 31 '14 at 14:02

gniourf_gniourf

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answered Oct 31 '14 at 13:53

Charles Duffy

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Requires bash 4 or greater for associative arrays. Also there's some IFS/read/heredoc/herestring bug that was fixed in some bash 4+ version that may or may not be relevant here (I forget the details unfortunately). – Etan Reisner Oct 31 '14 at 14:01
The current version as edited (thanks, @gniourf_gnioruf) works back on 4.0.35, so I don't believe we're depending on any recent fixes here. – Charles Duffy Oct 31 '14 at 14:04
Looks like the issue I was thinking of was leaking `IFS` to the redirection and was a `4.2` bug fixed in `4.3`. So yes, this is fine. (For the record it was never my intent to question that fact.) – Etan Reisner Oct 31 '14 at 16:13
Interesting -- I hadn't heard about that bug; will try to keep it in mind. Thanks! – Charles Duffy Oct 31 '14 at 16:15
Not the best resource but something at least. http://stackoverflow.com/questions/24929819/ifs-change-with-bash-4-2 – Etan Reisner Oct 31 '14 at 16:17

score 0 · Accepted Answer · answered Oct 31 '14 at 14:06

If you were willing to use awk, you could do something like this:

$ awk -F] -vRS="," '!(NR%2){++a[$1]}END{for(i in a)printf "%s: %s\n",i,a[i]}' <<<"[[some_str,another_str],[some_str,the_str],[some_str,the_str],[some_str,whatever_str]]"
whatever_str: 1
another_str: 1
the_str: 2

Set the field separator to ] and the record separator to ,. Count the occurrence of every second record. After all records have been processed, print the results.

Processing string in BASH and count the number of a substring beeing seen

2 Answers2