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Compatibility with bash

grfsh implements the bash features that real scripts use most. A compatibility suite runs 40 scripts through bash 5.3 and grfsh on every change and compares their output byte for byte, and installers for rustup, nvm, Homebrew, Docker and oh-my-zsh are checked with grfsh --check in CI.

Supported

Section titled “Supported”
  • Simple commands, pipelines, &&, ||, !, ;, &, subshells and groups
  • if, while, until, for, C style for (( )), case with ;;, ;& and ;;&, functions
  • [[ ]] with ==, !=, =~ and BASH_REMATCH, <, >, -eq and the file tests, [ and test
  • Parameter expansion: defaults, alternatives, errors, assignment, length, substrings, prefix and suffix removal, replacement, case changes, ${!name}, ${!prefix*}, ${!array[@]} and the @Q, @E, @U, @u, @L and @a transforms
  • Arithmetic: $(( )), (( )), all C operators, **, base#digits, hex and octal literals
  • Indexed arrays (sparse, negative indexes, slices) and associative arrays
  • Brace expansion with lists, ranges, padding and steps, tilde expansion
  • Command substitution, process substitution, here documents, here strings
  • Globs with *, ?, [...], character classes, ** with globstar, nullglob, dotglob and nocaseglob
  • Redirections on any file descriptor, including 2>&1, &>, >&- and exec 3>file
  • set -e, -u, -x, -o pipefail, trap for signals, EXIT and ERR
  • getopts, read with its common flags, printf with -v, mapfile, declare and friends
  • $PIPESTATUS, $LINENO, $SECONDS, $RANDOM, $PPID, $BASH_REMATCH, $FUNCNAME, $BASH_SOURCE
  • Job control: &, jobs, fg, bg, wait, kill %n, Ctrl-Z

Not supported

Section titled “Not supported”

grfsh --check reports each of these with its line number.

Feature Alternative
shopt -s extglob patterns such as !(x) and @(a|b) case patterns, or files | where name =~ ...
declare -n and local -n name references ${!name}, printf -v "$name"
coproc process substitution or named pipes
select menus read -p with case
let (( ))
trap ... DEBUG none
caller, enable, hash, fc, bind, compgen, suspend, disown see grfsh --check hints
$BASH_VERSINFO, $BASH_LINENO none yet

POSIX sh

Section titled “POSIX sh”

grfsh is not a POSIX shell. It runs POSIX scripts that stay within the features above, which covers most of them, but it is not tested for strict POSIX conformance. Keep /bin/sh as it is.