libsmartcols: sanitize variable names on export output

The shells are very restrictive about variable names, only [:alnum:]
chars are allowed (and alphabetic chars as the first char).  The
library will replace "bad" chars with "_". The char '%' at the end is
replaced by _PCT.

Addresses: https://github.com/karelzak/util-linux/issues/1201
Signed-off-by: Karel Zak <kzak@redhat.com>

include/carefulputc.h

@@ -151,5 +151,21 @@ static inline void fputs_nonblank(const char *data, FILE *out)
 	}
 }
 
+static inline void fputs_shell_ident(const char *data, FILE *out)
+{
+	const char *p = data;
+
+	/* convert "1FOO" to "_1FOO" */
+	if (p && !isalpha(*p))
+		fputc('_', out);
+
+	/* replace all "bad" chars with "_" */
+	for (p = data; p && *p; p++) {
+		if (!isalnum(*p))
+			fputc('_', out);
+		else
+			fputc(*p, out);
+	}
+}
 
 #endif  /*  _CAREFULPUTC_H  */

libsmartcols/src/print.c

@@ -472,7 +472,10 @@ static int print_data(struct libscols_table *tb,
 		return 0;
 
 	case SCOLS_FMT_EXPORT:
-		fprintf(tb->out, "%s=", name);
+		fputs_shell_ident(name, tb->out);
+		if (endswith(name, "%"))
+			fputs("PCT", tb->out);
+		fputc('=', tb->out);
 		fputs_quoted(data, tb->out);
 		if (!is_last)
 			fputs(colsep(tb), tb->out);

libsmartcols/src/table.c

@@ -1076,6 +1076,10 @@ int scols_table_enable_json(struct libscols_table *tb, int enable)
  * Enable/disable export output format (COLUMNAME="value" ...).
  * The parsable output formats (export and raw) are mutually exclusive.
  *
+ * Note that COLUMNAME maybe be modified on output to contains only chars
+ * allowed as shell variable identifiers, for example MIN-IO and FSUSE% will be
+ * MIN_IO and FSUSE_PCT.
+ *
  * Returns: 0 on success, negative number in case of an error.
  */
 int scols_table_enable_export(struct libscols_table *tb, int enable)

misc-utils/findmnt.8

@@ -156,7 +156,9 @@ Output almost all available columns.  The columns that require
 are not included.
 .TP
 .BR \-P , " \-\-pairs"
-Use key="value" output format.  All potentially unsafe characters are hex-escaped (\\x<code>).
+Produce output in the form of key="value" pairs.  All potentially unsafe value characters are hex-escaped (\\x<code>).
+The key (variable name) will be modified to contain only characters allowed for a shell variable
+identifiers, for example, FS_OPTIONS and USE_PCT instead of FS-OPTIONS and USE%.
 .TP
 .BR \-p , " \-\-poll\fR[\fI=list\fR]"
 Monitor changes in the /proc/self/mountinfo file.  Supported actions are: mount,

misc-utils/lsblk.8

@@ -128,7 +128,9 @@ Output all available columns.
 .TP
 .BR \-P , " \-\-pairs"
 Produce output in the form of key="value" pairs.  The output lines are still ordered by
-dependencies.  All potentially unsafe characters are hex-escaped (\\x<code>).
+dependencies.  All potentially unsafe value characters are hex-escaped (\\x<code>).
+The key (variable name) will be modified to contain only characters allowed for a shell variable
+identifiers, for example, MIN_IO and FSUSE_PCT instead of MIN-IO and FSUSE%.
 .TP
 .BR \-p , " \-\-paths"
 Print full device paths.

sys-utils/lsipc.1

@@ -51,7 +51,10 @@ Write information about active semaphore sets.
 Show creator and owner.
 .TP
 \fB\-e\fR, \fB\-\-export\fR
-Output data in the format of NAME=VALUE.
+Produce output in the form of key="value" pairs.  All potentially unsafe value
+characters are hex-escaped (\\x<code>).  The key (variable name) will be
+modified to contain only characters allowed for a shell variable identifiers,
+for example, USE_PCT instead of USE%.
 .TP
 \fB\-J\fR, \fB\-\-json\fR
 Use the JSON output format.

sys-utils/lsmem.1

@@ -61,8 +61,8 @@ specified in the format \fB+\fIlist\fP (e.g., \fBlsmem \-o +NODE\fP).
 Output all available columns.
 .TP
 .BR \-P , " \-\-pairs"
-Produce output in the form of key="value" pairs.
-All potentially unsafe characters are hex-escaped (\\x<code>).
+Produce output in the form of key="value" pairs.  All potentially unsafe value
+characters are hex-escaped (\\x<code>).
 .TP
 .BR \-r , " \-\-raw"
 Produce output in raw format.  All potentially unsafe characters are hex-escaped