https://will-keleher.com/posts/5-Useful-Bash-Patterns.html

posts about rss
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Bash Patterns I Use Weekly

1. Find and replace a pattern in a codebase with capture groups

git grep -l pattern | xargs gsed -ri 's|pat(tern)|\1s are birds|g'

  * git grep -l: make sure we're only looking for files in our
    codebase (ag -l is another good option)
  * xargs: allow running this with gsed -i
  * gsed -i: edit files (default mac sed is bad, so gnu-sed is
    essential)
  * gsed -r: use regular expression for the pattern to allow capture
    groups
  * s|: the first character after the s is used as the delimiter. /
    is pretty consistently annoying because it's used in file paths &
    urls.
  * gsed '...': the single quotes are important to avoid escapes
  * 's|pat(tern)|\1s are birds|g': being able to easily use capture
    groups in a find and replace is amazing
  * |g: replace this multiple times in a line

2. Track down a commit when a command started failing

while command; do git checkout HEAD^; done;

  * while command: As long as command exits successfully (with a 0),
    this loop will keep going. (this is why while true; works! The
    same thing works with if: if git grep yay; then echo "found yay";
    fi)
  * git checkout HEAD^: go back in time.
  * git bisect is the "real" way to do this, but it's not something
    I've ever needed, and while command and while ! command are both
    generally useful to know
  * A similar pattern to poll until something succeeds could be while
    ! curl localhost:8080; do sleep 1; done;.

3. Parallelize running commands by grabbing PIDs.

pids="";
do_thing_1 &
pids="$pids $!"
do_thing_2 &
pids="$pids $!"
EXIT_CODE=0
for p in $pids; do
  if ! wait $p; then EXIT_CODE=1; fi
done

exit $EXIT_CODE;

4. Use $SECONDS to track how long things take

echo "Your command completed after $SECONDS seconds";

  * Try running this in your shell: SECONDS=0; sleep 5; echo
    $SECONDS;
  * I often prefer this over time when setting up logs for a script

5. Use for to iterate over simple lists:

for route in foo bar baz; do
  curl localhost:8080/$route
done

The default separator in bash is a space, and you can take advantage
of this to make simple for loops. (This default is quite frustrating
to work around in general: spaces in file names are the devil.)