implement env

Fixes: #167

README.md

@@ -46,7 +46,7 @@ count below and mark it as done in this README.md. Thanks!
 GNU coreutils. They are not 100% compatiable. If you encounter different behaviors,
 compare against the true GNU coreutils version on the Linux-based tests first.
 
-## Completed (66/109)
+## Completed (67/109)
 
 |  Done   | Cmd       | Descripton                                       |
 | :-----: | --------- | ------------------------------------------------ |
@@ -77,7 +77,7 @@ compare against the true GNU coreutils version on the Linux-based tests first.
 | ✓ | dirname   | Strip last file name component                   |
 |         | du        | Estimate file space usage                        |
 | ✓ | echo      | Print a line of text                             |
-|         | env       | Run a command in a modified environment          |
+| ✓ | env       | Run a command in a modified environment          |
 | ✓ | expand    | Convert tabs to spaces                           |
 | ✓ | expr      | Evaluate expressions                             |
 | ✓ | factor    | Print prime factors                              |

src/env/args.v

@@ -0,0 +1,38 @@
+import common
+
+const app_name = 'env'
+const app_description = 'run a program in a modified environment'
+
+struct EnvArg {
+	// -0
+	nul_terminated bool
+
+	// -u
+	unsets []string
+
+	// -i
+	ignore bool
+
+	// command and arguments
+	cmd_args []string
+}
+
+pub fn new_args(args []string) !EnvArg {
+	mut fp := common.flag_parser(args)
+	fp.application(app_name)
+	fp.description(app_description)
+	fp.version(common.coreutils_version())
+
+	nul := fp.bool('null', `0`, false, 'end each output line with NUL, not newline')
+	unsets := fp.string_multi('unset', `u`, 'remove variable from the environment')
+	ignore := fp.bool('ignore-environment', `i`, false, 'start with an empty environment')
+
+	cmd_args := fp.finalize() or { return err }
+
+	return EnvArg{
+		nul_terminated: nul
+		unsets:         unsets
+		ignore:         ignore
+		cmd_args:       cmd_args
+	}
+}

src/env/args_test.v

@@ -0,0 +1,15 @@
+module main
+
+fn test_ignore() {
+	args := new_args(['t', '-i'])!
+	assert args.ignore == true
+}
+
+fn test_unset() {
+	args := new_args(['t', '-i', '-u', 'ABC'])!
+	assert 'ABC' in args.unsets
+
+	multi_args := new_args(['t', '-i', '-u', 'ABC', '-u', 'EFG'])!
+	assert 'ABC' in multi_args.unsets
+	assert 'EFG' in multi_args.unsets
+}

src/env/env.v

@@ -0,0 +1,40 @@
+// env - run a program in a modified environment
+import os
+import maps
+
+fn main() {
+	args := new_args(os.args) or {
+		eprintln(err)
+		return
+	}
+	run(args)
+}
+
+pub fn run(args EnvArg) {
+	mut envs := if args.ignore {
+		map[string]string{}
+	} else {
+		os.environ()
+	}
+
+	for key in args.unsets {
+		envs.delete(key)
+	}
+
+	if args.cmd_args.len == 0 {
+		eol := if args.nul_terminated { '\0' } else { '\n' }
+		for key, val in envs {
+			print('${key}=${val}' + eol)
+		}
+		return
+	}
+
+	cmd_path := os.find_abs_path_of_executable(args.cmd_args[0]) or {
+		eprintln(err)
+		return
+	}
+
+	os.execve(cmd_path, args.cmd_args[1..], maps.to_array(envs, fn (k string, v string) string {
+		return '${k}=${v}\0'
+	})) or { eprintln(err) }
+}

src/env/env_test.v

@@ -0,0 +1,25 @@
+import os
+
+fn test_help() {
+	result := os.execute_or_panic('${os.quoted_path(@VEXE)} run . -h')
+	assert result.exit_code == 0
+	assert result.output.contains('a modified environment')
+}
+
+fn test_same_env() {
+	result := os.execute_or_panic('${os.quoted_path(@VEXE)} run . -0')
+	assert result.exit_code == 0
+
+	env := os.execute_or_panic('env -0')
+	assert env.exit_code == 0
+	assert env.output == result.output
+}
+
+fn test_same_unset() {
+	result := os.execute_or_panic('${os.quoted_path(@VEXE)} run . -u PATH')
+	assert result.exit_code == 0
+
+	env := os.execute_or_panic('env -u PATH')
+	assert env.exit_code == 0
+	assert env.output == result.output
+}