Bash string manipulation without external tools

Parameter Expansion: Fast String Ops in Pure Bash

Bash's parameter expansion handles most string operations without spawning subprocesses. Prefer it over $(echo ... | sed) for performance.

path="/home/alice/projects/myapp.tar.gz"

# Length
echo ${#path}            # 35

# Substring: ${var:start:length}
echo ${path:6:5}         # alice

# Strip prefix (shortest match)
echo ${path#*/}          # home/alice/projects/myapp.tar.gz

# Strip prefix (longest match)
echo ${path##*/}         # myapp.tar.gz  (basename)

# Strip suffix (shortest match)
echo ${path%.*}          # /home/alice/projects/myapp.tar

# Strip suffix (longest match)
echo ${path%%.*}         # /home/alice/projects/myapp

# Replace first match
echo ${path/projects/repos}  # /home/alice/repos/myapp.tar.gz

# Replace all matches
echo ${path//\//_}       # _home_alice_projects_myapp.tar.gz

Default Values and Validation

name="${1:-world}"        # default if $1 is unset or empty
port="${PORT:=8080}"      # assign default if PORT is unset

# Fail if variable is unset
: "${REQUIRED_VAR:?Error: REQUIRED_VAR must be set}"

Case Conversion (Bash 4+)

str="Hello World"
echo ${str,,}   # hello world  (lowercase)
echo ${str^^}   # HELLO WORLD  (uppercase)

Case conversion requires Bash 4+. macOS ships Bash 3 by default — install Bash via Homebrew for scripts targeting both platforms.