Bash

Man pages

Special parameters

Array expansion

${SOME_ARRAY[@]}

Returning values from script

// some behavior
 
echo "$WHATEVER"

Linting

koalaman/shellcheck, available as a docker image, see Linting

Script arguments

Take the nth argument onwards

${@:2} - would take only argument 2 and on

e.g.

Say we had a script run-stuff.sh:

docker run \
	--rm \
	"sometag:someversion" \
	"${@:2}"

We can call it like this:

/path/to/run-stuff.sh "some argument" "some other argument" "a third argument"

And only "some argument" and "a third argument" would be passed to the docker run command.

Conditionals

Check for empty array

if [ ${#SOME_ARRAY[@]} -eq 0 ]; then

Check for absence of a file (remove ! to check for existence)

if [ ! -f /path/to/file ]; then

chmod +x vs. chmod 755

Code churn

Intuition is great but we often forget that we can use churn stats too.

find . -name "*.rb" |xargs -n1 -I file sh -c 'echo `git log --oneline file | wc -l`: file'|sort -nr

Applying a time period window is good too as some parts of code churn for a while and them reach stability.

Bash redirects

Untitled

Read contents of gzipped file without unzipping

zcat file | less - can obviously also be chained with grep

Grep through all gzipped files in a directory

find . -name \*.gz -print0 | xargs -0 zgrep --line-number "{search pattern}”

Grep through non-gzipped files in a directory

find . -name \*.{file ext} -print0 | xargs -0 grep --line-number "{search pattern}”

Jesse's Notes