[PATCH 2/5] cmd: Add support for (limited) command substitution

[Sean Anderson]

On 2/28/21 6:59 PM, Heinrich Schuchardt wrote:
> Am 1. März 2021 00:47:15 MEZ schrieb Sean Anderson <seanga2 at gmail.com>:
>> The traditional way to grab the output from a shell script is to use
>> command substitution. Unfortunately, we don't really have the concept
>> of
>> pipes in U-Boot (at least not without console recording). Even if we
>> did,
>> stdout is severely polluted by informational printfs.
>>
>> Instead of redirecting stdout, instead use a special global variable.
>> This
>> lets commands set a result without having to modify the function
>> signature
>> of every command, and everything that calls commands. This is a bit of
>> a
>> hack, but seemed like the least-invasive of all options.
>>
>> Currently, the value of cmd_result is printed if it is set. This makes
>> sense for things like echo, where you can do something like
>>
>> 	=> echo a b c d e
>> 	a b c d e
>> 	=> var=c
>> 	=> echo a $(echo b $var d) e
>> 	a b c d e
>>
>> but it makes less sense for some other commands
>>
>> All callers of cmd_process must
>> 	1. Print cmd_result (unless it is being "redirected")
>> 	2. free() cmd_result
>> 	3. set cmd_result to NULL
>> Calling cmd_process with a non-NULL value in cmd_result is a bug.
> 
> I don't understand what you are changing from the lines above.

> => echo a $(echo b $var d) e

This is a syntax error at the moment, and this series makes it work.

> 
> Before extending the hush shell we should write a man-page in doc/usage/ describing what it actually does.

What would it be named? Is there an existing section of the
documentation which documents the standard and non-standard features of
hush?

> 
> Building in new gimmicks without documentation does not make any sense to me.

Yes, this should likely be better-documented. However, I'm not sure that
this approach is the best one, so I wanted to get some feedback before
writing out documentation. I suppose this makes this an RFC series.

--Sean

> 
> Best regards
> 
> Heinrich
> 
> 
>>
>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
>> ---
>>
>> common/cli_hush.c                 | 39 ++++++++++++++++++++++++++++---
>> common/cli_simple.c               |  8 ++++++-
>> common/command.c                  |  3 +++
>> include/asm-generic/global_data.h |  4 ++++
>> 4 files changed, 50 insertions(+), 4 deletions(-)
>>
>> diff --git a/common/cli_hush.c b/common/cli_hush.c
>> index 83329763c6..8fed7eb14e 100644
>> --- a/common/cli_hush.c
>> +++ b/common/cli_hush.c
>> @@ -475,6 +475,8 @@ static char *make_string(char **inp, int *nonnull);
>> static int handle_dollar(o_string *dest, struct p_context *ctx, struct
>> in_str *input);
>> #ifndef __U_BOOT__
>> static int parse_string(o_string *dest, struct p_context *ctx, const
>> char *src);
>> +#else
>> +static void update_ifs_map(void);
>> #endif
>> static int parse_stream(o_string *dest, struct p_context *ctx, struct
>> in_str *input0, int end_trigger);
>> /*   setup: */
>> @@ -1673,6 +1675,10 @@ static int run_pipe_real(struct pipe *pi)
>> 					"'run' command\n", child->argv[i]);
>> 			return -1;
>> 		}
>> +		if (gd->cmd_result)
>> +			puts(gd->cmd_result);
>> +		free(gd->cmd_result);
>> +		gd->cmd_result = NULL;
>> 		/* Process the command */
>> 		return cmd_process(flag, child->argc - i, child->argv + i,
>> 				   &flag_repeat, NULL);
>> @@ -2683,6 +2689,7 @@ FILE *generate_stream_from_list(struct pipe
>> *head)
>> #endif
>> 	return pf;
>> }
>> +#endif /* __U_BOOT__ */
>>
>> /* this version hacked for testing purposes */
>> /* return code is exit status of the process that is run. */
>> @@ -2691,7 +2698,11 @@ static int process_command_subs(o_string *dest,
>> struct p_context *ctx, struct in
>> 	int retcode;
>> 	o_string result=NULL_O_STRING;
>> 	struct p_context inner;
>> +#ifdef __U_BOOT__
>> +	int list_retcode;
>> +#else
>> 	FILE *p;
>> +#endif
>> 	struct in_str pipe_str;
>> 	initialize_context(&inner);
>>
>> @@ -2702,13 +2713,21 @@ static int process_command_subs(o_string *dest,
>> struct p_context *ctx, struct in
>> 	done_pipe(&inner, PIPE_SEQ);
>> 	b_free(&result);
>>
>> +#ifdef __U_BOOT__
>> +	list_retcode = run_list_real(inner.list_head);
>> +	setup_string_in_str(&pipe_str, gd->cmd_result ?: "");
>> +	/* Restore the original map as best we can */
>> +	update_ifs_map();
>> +#else
>> 	p=generate_stream_from_list(inner.list_head);
>> 	if (p==NULL) return 1;
>> 	mark_open(fileno(p));
>> 	setup_file_in_str(&pipe_str, p);
>> +#endif
>>
>> 	/* now send results of command back into original context */
>> 	retcode = parse_stream(dest, ctx, &pipe_str, '\0');
>> +#ifndef __U_BOOT__
>> 	/* XXX In case of a syntax error, should we try to kill the child?
>> 	 * That would be tough to do right, so just read until EOF. */
>> 	if (retcode == 1) {
>> @@ -2723,12 +2742,18 @@ static int process_command_subs(o_string *dest,
>> struct p_context *ctx, struct in
>> 	 * to the KISS philosophy of this program. */
>> 	mark_closed(fileno(p));
>> 	retcode=pclose(p);
>> +#else
>> +	free(gd->cmd_result);
>> +	gd->cmd_result = NULL;
>> +	retcode = list_retcode;
>> +#endif
>> 	free_pipe_list(inner.list_head,0);
>> 	debug_printf("pclosed, retcode=%d\n",retcode);
>> 	/* XXX this process fails to trim a single trailing newline */
>> 	return retcode;
>> }
>>
>> +#ifndef __U_BOOT__
>> static int parse_group(o_string *dest, struct p_context *ctx,
>> 	struct in_str *input, int ch)
>> {
>> @@ -2896,11 +2921,11 @@ static int handle_dollar(o_string *dest, struct
>> p_context *ctx, struct in_str *i
>> 			}
>> 			b_addchr(dest, SPECIAL_VAR_SYMBOL);
>> 			break;
>> -#ifndef __U_BOOT__
>> 		case '(':
>> 			b_getch(input);
>> 			process_command_subs(dest, ctx, input, ')');
>> 			break;
>> +#ifndef __U_BOOT__
>> 		case '*':
>> 			sep[0]=ifs[0];
>> 			for (i=1; i<global_argc; i++) {
>> @@ -3165,7 +3190,7 @@ static void update_ifs_map(void)
>> 		mapset(subst, 3);       /* never flow through */
>> 	}
>> 	mapset((uchar *)"\\$'\"", 3);       /* never flow through */
>> -	mapset((uchar *)";&|#", 1);         /* flow through if quoted */
>> +	mapset((uchar *)";&|()#", 1);         /* flow through if quoted */
>> #endif
>> 	mapset(ifs, 2);            /* also flow through if quoted */
>> }
>> @@ -3185,7 +3210,8 @@ static int parse_stream_outer(struct in_str *inp,
>> int flag)
>> 		ctx.type = flag;
>> 		initialize_context(&ctx);
>> 		update_ifs_map();
>> -		if (!(flag & FLAG_PARSE_SEMICOLON) || (flag & FLAG_REPARSING))
>> mapset((uchar *)";$&|", 0);
>> +		if (!(flag & FLAG_PARSE_SEMICOLON) || (flag & FLAG_REPARSING))
>> +			mapset((uchar *)";$&|()", 0);
>> 		inp->promptmode=1;
>> 		rcode = parse_stream(&temp, &ctx, inp,
>> 				     flag & FLAG_CONT_ON_NEWLINE ? -1 : '\n');
>> @@ -3205,6 +3231,13 @@ static int parse_stream_outer(struct in_str
>> *inp, int flag)
>> 			run_list(ctx.list_head);
>> #else
>> 			code = run_list(ctx.list_head);
>> +
>> +			if (!(flag & FLAG_REPARSING) && gd->cmd_result) {
>> +				puts(gd->cmd_result);
>> +				free(gd->cmd_result);
>> +				gd->cmd_result = NULL;
>> +			}
>> +
>> 			if (code == -2) {	/* exit */
>> 				b_free(&temp);
>> 				code = 0;
>> diff --git a/common/cli_simple.c b/common/cli_simple.c
>> index e80ba488a5..5df30d964f 100644
>> --- a/common/cli_simple.c
>> +++ b/common/cli_simple.c
>> @@ -15,14 +15,16 @@
>> #include <console.h>
>> #include <env.h>
>> #include <log.h>
>> +#include <malloc.h>
>> #include <linux/ctype.h>
>>
>> +DECLARE_GLOBAL_DATA_PTR;
>> +
>> #define DEBUG_PARSER	0	/* set to 1 to debug */
>>
>> #define debug_parser(fmt, args...)		\
>> 	debug_cond(DEBUG_PARSER, fmt, ##args)
>>
>> -
>> int cli_simple_parse_line(char *line, char *argv[])
>> {
>> 	int nargs = 0;
>> @@ -257,6 +259,10 @@ int cli_simple_run_command(const char *cmd, int
>> flag)
>>
>> 		if (cmd_process(flag, argc, argv, &repeatable, NULL))
>> 			rc = -1;
>> +		if (gd->cmd_result)
>> +			puts(gd->cmd_result);
>> +		free(gd->cmd_result);
>> +		gd->cmd_result = NULL;
>>
>> 		/* Did the user stop this? */
>> 		if (had_ctrlc())
>> diff --git a/common/command.c b/common/command.c
>> index 3fe6791eda..952a8f00eb 100644
>> --- a/common/command.c
>> +++ b/common/command.c
>> @@ -588,6 +588,9 @@ enum command_ret_t cmd_process(int flag, int argc,
>> char *const argv[],
>> 	enum command_ret_t rc = CMD_RET_SUCCESS;
>> 	struct cmd_tbl *cmdtp;
>>
>> +	/* Clear previous result */
>> +	assert(!gd->cmd_result);
>> +
>> #if defined(CONFIG_SYS_XTRACE)
>> 	char *xtrace;
>>
>> diff --git a/include/asm-generic/global_data.h
>> b/include/asm-generic/global_data.h
>> index b6a9991fc9..85262d9566 100644
>> --- a/include/asm-generic/global_data.h
>> +++ b/include/asm-generic/global_data.h
>> @@ -453,6 +453,10 @@ struct global_data {
>> 	 */
>> 	char *smbios_version;
>> #endif
>> +	/**
>> +	 * @cmd_result: Result of the current command
>> +	 */
>> +	char *cmd_result;
>> };
>>
>> /**
>