Bash Tip: Read From File or STDIN

Posted on 2020-07-18 in Programming

# Usage:
# foo.txt > foo_but_better.txt
#   cat bar.txt | tr '[:lower:]' '[:upper:]' | > BAR_BUT_BETTER.txt

cat ${1:--} \
  | sed -e 's/pipe/line/g'

Sometimes I write a bash script that needs to play nicely in the middle of a pipeline, but it would also be nice to use it at the front of the pipeline or on its own. This snippet says, "cat whatever the first parameter is, or if there's no first parameter, then cat the content of STDIN".