linux - Bash - variables are not evaluated inside other variables -

i've written short script needs find text using regex.

i'm incrementing counter inside while loop, , counter part of command. unfortunately command running initial counter.

here snippet code:

counter=1 last_commit=`git log remotes/origin/devel --pretty=oneline --pretty=format:%s | head -${counter}` jira_id=`echo $last_commit | grep -o -p '[a-z]{2,}-\d+' | xargs`  while [[ ! -z "$jira_id" && $counter -lt "5" ]];         echo "this current  counter:  $counter"         echo "this last commit $last_commit"         counter=$[counter+1] done echo "this counter outside loop $counter" 

the best-practices way encapsulate code (as per bashfaq #50) function:

get_last_commit() {   git log remotes/origin/devel --pretty=oneline --pretty=format:%s \     | sed -n "$(( $1 + 1)) p" } 

then:

while (( counter < 5 ));   last_commit=$(get_last_commit "$counter")   ifs=$'\n' read -r -d '' -a jira_id \     < <(grep -o -p '[a-z]{2,}-\d+' <<<"$last_commit") ||:   [[ $jira_id ]] || break    echo "this current  counter:  $counter"   echo "this last commit $last_commit"   echo "found ${#jira_id[@]} jira ids"   printf '  %s\n' "${jira_id[@]}"    (( counter++ )) done 

other notes:

• use of read -a, here, reads jira ids array; can ask array's length (with ${#jira_id[@]}), expand specific entry array (with ${jira_id[0]} first id, [1] second, etc); expand them argument list (with "${jira_id[@]}"), etc.
• non-system-defined shell variables should have @ least 1 lower-case character in names. see fourth paragraph of posix spec on environment variables @ http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html, keeping in mind environment variables , shell variables share single namespace. following practice prevents overwriting system variables mistake.
• $(( ... )) posix-standard way enter math context; (( )), without leading $, bash extension.
• while code inside of [[ ]] , (( )) not require double quotes prevent glob expansion or string-splitting, double quotes should used around expansions in (almost) other cases.
• sed '2 p' gets line 2 more efficiently head -2 | tail -n 1.

---

however, less efficient calling git log 1 single time , iterating on results.

while ifs= read -r -u 3 last_commit;   ifs=$'\n' read -r -d '' -a jira_id \     < <(grep -o -p '[a-z]{2,}-\d+' <<<"$last_commit") ||:   [[ $jira_id ]] || continue   echo "found ${#jira_id[@]} jira ids"   printf '  %s\n' "${jira_id[@]}" done 3< <(git log remotes/origin/devel --pretty=oneline --pretty=format:%s)