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Linux: ss64.com/bash/grep.html

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Get line from file

Get bundler version from lock file, which has a title on one line and version on the next (and in this case always the last line of the file).

# Gemfile.lock

# ...
# ...
BUNDLED WITH:
  1.17.2

$ VSN="$(grep -A 1 "BUNDLED WITH" Gemfile.lock | tail -n 1)"

Notes:

  • If the file does not exist, grep will show a warning on stderr. If you are existing on errors you can continue.
  • If file does not contain the line, grep will exit on a success code still and the value will be an empty string.
  • Use -A 1 as an offset so we get the line after it. And then tail to keep it one line - don’t know what happens if there’s more content after it.

Use-case:

$ BUNDLE_VSN=gem install bundler \
-v "$(grep -A 1 '"BUNDLED WITH'" Gemfile.lock | tail -n 1)"
$ gem install bundler -v "${BUNDLE_VSN:-2.1.4}"

Copied from source.

Whitespace does not matter here but in other cases could be trimmed.