Parameter expansion toolkit

basename, strip extension, and global replace without spawning sed/basename

f=/var/log/app.log.gz; echo "${f##*/}" "${f%.*}" "${f//log/LOG}"
tool
bash12 commands
tags
bashperformance

More bash commands

  • Regex capture with BASH_REMATCH
    [[ $s =~ ^([0-9]+)\.([0-9]+) ]] && echo "${BASH_REMATCH[1]}/${BASH_REMATCH[2]}"

    Native regex match extracts groups; note: don't quote the right-hand regex

  • Parallel xargs over null-delimited input
    find . -name '*.log' -print0 | xargs -0 -P"$(nproc)" -n1 gzip

    Run N parallel jobs safely with NUL separators for names with spaces

  • Check PIPESTATUS of each stage
    curl -s "$url" | jq .data; echo "${PIPESTATUS[@]}"

    Inspect exit code of every pipe stage; $? only reports the last command

  • getopts flag parsing
    while getopts "n:v" o; do case $o in n) ns=$OPTARG;; v) verbose=1;; esac; done

    POSIX option parsing with arguments; -n takes a value, -v is a switch

  • Bound command with timeout and kill
    timeout -k 5s 30s ./long_task.sh || echo "timed out: $?"

    SIGTERM at 30s then SIGKILL after 5s grace; exit 124 means it was killed

all 12 bash commands