Shell script to add go.mod replace directives when working with multiple local modules

go-mod-local

#!/bin/bash

usage() {
  cat <<__usage__
-- DESCRIPTION -----------------------------------------------------------------

  Insert a 'replace' directive into each given Go module (default: PWD) that 
  defines a local file path of a Go package to import instead of the published
  package named in any of the given modules' import lists. 

-- SYNOPSIS --------------------------------------------------------------------

  ${0##*/} IMPORT PATH [MODULE ...] 

-- ARGUMENTS -------------------------------------------------------------------

  - IMPORT    Package path used in Go import clauses

  - PATH      Local filepath to use for the imported package

  - MODULE    (optional) Local filepath of Go module to modify
                 default: $PWD
__usage__
  exit
}

# halt prints an error message to stderr and exits the script with the given
# status code. The error message is provided as a printf-style format string
# and associated parameters.
#  % halt [STATUS [FORMAT [PARAM...]]]
halt() {
	local ret=${1:-127}
	local pre='error' msg=${2:-'(unspecified)'}
	[[ $ret =~ ^[0-9]*$ ]] ||
		ret=126
	[[ $# -gt 0 && $1 -eq 0 ]] &&
		pre='exit' msg=${2:-'OK'}
	[[ $# -ge 3 ]] &&
		msg=$( printf -- "${2}" "${@:3}" )
	printf -- '%s(%d): %s\n' "${pre}" ${ret} "${msg}" >&2
	exit ${ret}
}

relpath() {
  [ $# -ge 2 ] &&
    perl -MFile::Spec::Functions=abs2rel -le \
      'print abs2rel(@ARGV)' "${2}" "${1}"
}

replace() {
  [ $# -ge 2 ] || return 1
  go mod edit -replace "${1}=${2}"
  go mod tidy
}

[ $# -ge 2 ] || usage

module=( "${@:3}" )
[ ${#module[@]} -gt 0 ] || module=( "$PWD" )

for mod in "${module[@]}"; do
  [ -d "$mod" ] && mod="$mod/go.mod"
  [ "${mod##*/}" = "go.mod" ] && [ -f "$mod" ] ||
    halt 100 "module file invalid or not found: %s" "$mod"
  path=${mod%/go.mod}

  pushd "$path" &>/dev/null ||
    halt 101 "failed to open directory: %s" "$path"
  replace "$1" "$( relpath "${PWD}" "$2" )" ||
    halt 102 "command failed: %s" "go mod edit / tidy"
  popd &>/dev/null
done

I can never remember the syntax used in the go.mod file, and I recently found a need to update multiple modules at once.

TODO

• Add a flag to remove the directive from a given list of modules

Warning

This script should no longer be used.

Tip

Go 1.18 added support for multi-module workspaces. You should now use a replace directive in go.work to replace paths in multiple modules.