07-28-2008
The double quotes are mainly for safety (good habit in case $h ends up containing an empty string by mistake, for example) and in theory, the && variant could create two external processes where -a would only create one. (It's theory because [ is probably handled internally in moderns shells, so there is no external process involved.)
Shell scripts are not parsed much, the syntax is more shallow than in many other scripting languages and this creates some complications, but also helps make the shell extremely versatile. The lack of standard, built-in arithmetic operators right from the start is another source of complexity in this case. POSIX attempts to fix some of the issues but historically, different shells have developed different extensions which have then created, as it were, even more different ways to skin a cat.
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LEARN ABOUT CENTOS
execute
EXECUTE(7) PostgreSQL 9.2.7 Documentation EXECUTE(7)
NAME
EXECUTE - execute a prepared statement
SYNOPSIS
EXECUTE name [ ( parameter [, ...] ) ]
DESCRIPTION
EXECUTE is used to execute a previously prepared statement. Since prepared statements only exist for the duration of a session, the
prepared statement must have been created by a PREPARE statement executed earlier in the current session.
If the PREPARE statement that created the statement specified some parameters, a compatible set of parameters must be passed to the EXECUTE
statement, or else an error is raised. Note that (unlike functions) prepared statements are not overloaded based on the type or number of
their parameters; the name of a prepared statement must be unique within a database session.
For more information on the creation and usage of prepared statements, see PREPARE(7).
PARAMETERS
name
The name of the prepared statement to execute.
parameter
The actual value of a parameter to the prepared statement. This must be an expression yielding a value that is compatible with the data
type of this parameter, as was determined when the prepared statement was created.
OUTPUTS
The command tag returned by EXECUTE is that of the prepared statement, and not EXECUTE.
EXAMPLES
Examples are given in the EXAMPLES section of the PREPARE(7) documentation.
COMPATIBILITY
The SQL standard includes an EXECUTE statement, but it is only for use in embedded SQL. This version of the EXECUTE statement also uses a
somewhat different syntax.
SEE ALSO
DEALLOCATE(7), PREPARE(7)
PostgreSQL 9.2.7 2014-02-17 EXECUTE(7)