builtin_string: add pad command

doc_src/cmds/string-pad.rst

@@ -0,0 +1,42 @@
+string-pad - pad characters before and after string
+========================================
+
+Synopsis
+--------
+
+.. BEGIN SYNOPSIS
+
+::
+
+    string pad [(-l | --left)] [(-r | --right)] [(-c | --char) CHAR] [(-n | --count) INTEGER] [(-q | --quiet)] [STRING...]
+
+.. END SYNOPSIS
+
+Description
+-----------
+
+.. BEGIN DESCRIPTION
+
+``string pad`` pads before and after the string specified character for each STRING. If ``-l`` or ``--left`` is given, only padded before string. Left only is the default padding. If ``-r`` or ``--right`` is given, only padded after string. The ``-c`` or ``--char`` switch causes the characters in CHAR to be padded instead of whitespace. The ``-n`` or ``--count`` integer specifies the amount of characters to be padded. The default padding count is 0. Exit status: 0 if string was padded, or 1 otherwise.
+
+.. END DESCRIPTION
+
+Examples
+--------
+
+.. BEGIN EXAMPLES
+
+::
+
+    >_ string pad -l -n 10 -c ' ' 'abc'
+              abc
+
+    >_ string pad --right --count 5 --char=z foo bar
+    foozzzzz
+    barzzzzz
+
+    >_ string pad --left --right -n 5 --char=- foo
+    -----foo-----
+
+
+.. END EXAMPLES