How to add values to bash arrays? [duplicate]

Question

Sorry for the subject clone, but given that the technique I used successfully from that answer doesn't work as expected on a new script, I figured it was time for a new question.

Anyway, the following script is fairly straight forward:

missed_symbols=()

grep missed ${dest}/scribe.log | while read -r line; do
  symbol=$(echo "${line}" | cut -d' ' -f1)
  missed_symbols+=("$symbol")
done

grep missed ${dest}/scribe_close.log | while read -r line; do
  symbol=$(echo "${line}" | cut -d' ' -f1)
  missed_symbols+=("$symbol")
done

for symbol in "${missed_symbols[@]}"; do
  echo "Scribe missed a turn in ${symbol}"
done
echo "Scribe missed ${#missed_symbols[@]} turns today"
exit 0

And adding -x to the #!/bin/bash line tells me that, indeed, it is assigning the first word of each $line from $missed_symbols[@] to $symbol. Yet, when I check ${#missed_symbols[@]}, I get zero. And, of course, looping through it produces no output.

So, where's my typo?

Tip: shellcheck automatically recognizes many common issues like this — that other guy
– that other guy, Commented Nov 21, 2016 at 21:49
BTW -- using cut is bad form here; I really should have corrected that in my answer earlier rather than retaining it. See BashFAQ #100 for a general discussion of good practices for string manipulation in bash, or the bash-hackers page on parameter expansion for an in-depth discussion of the specific approach my updated answer is now using. — Charles Duffy
– Charles Duffy, Commented Nov 21, 2016 at 22:22
The stuff I write is almost always super simple, so I'm going to be making heavy use of ShellCheck. — pdm
– pdm, Commented Nov 22, 2016 at 15:52
Thank you, Charles, for your answer as well as clarification, even though this was a dupe. It's always nice when someone gives you the code you actually need to fix the problem, despite the answer being elsewhere in another form. — pdm
– pdm, Commented Nov 22, 2016 at 15:53

Charles Duffy · Accepted Answer · 2016-11-21 22:21:19Z

4

Pipelines create subshells. Changes to shell variables made in subshells disappear when those subshells exit.

Thus, instead of piping into a while read loop, redirect from a process substitution:

while read -r line; do
  symbol=${line%%" "*}
  missed_symbols+=("$symbol")
done < <(grep missed ${dest}/scribe.log)

edited Nov 21, 2016 at 22:21

answered Nov 21, 2016 at 21:37

Charles Duffy

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