Once a complete_command symbol has been recognized by the grammar (see [xref to 2.10 Shell Grammar]), the complete_command shall be subjected to alias substitution (see [xref to 2.3.1 Alias Substitution]) then executed before the next complete_command is tokenized and parsed.

After a token has been delimited, but before applying the grammatical rules in Section 2.10, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

After a sequeunce of tokens has been parsed and recognized as a command or compound list by the grammar (see [xref to 2.10 Shell Grammar]), but before the command or compound list is executed, each word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

With the $(command) form, all characters following the open parenthesis to the matching closing parenthesis constitute the command. Any valid shell script can be used for command, except a script consisting solely of redirections which produces unspecified results.

With the $(command) form, all characters following the open parenthesis to the matching closing parenthesis constitute the command.

With both the backquoted and $(command) forms, command shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed. Any valid compound_list can be used for command, except a compound_list consisting solely of redirections which produces unspecified results.

This variable, when and only when an interactive shell is invoked, shall be subjected to parameter expansion (see Section 2.6.2) by the shell and the resulting value shall be used as a pathname of a file containing shell commands to execute in the current environment.

This variable, when and only when an interactive shell is invoked, shall be subjected to parameter expansion (see Section 2.6.2) by the shell and the resulting value shall be used as a pathname of a file. Before any interactive commands are read, the contents of the file shall be tokenized, parsed, subjected to alias expansion, and executed as described in [xref to 2.3 Token Recognition]. The contents shall be executed in the current environment.

The shell shall execute commands from the file in the current environment.

The contents of file shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed in the current environment.

The constructed command shall be read and executed by the shell.

The constructed command shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed in the current environment.

/* The start symbol is compound_list when parsing dot scripts, command
   substitution bodies, and the arguments passed to eval */

Because a complete_command is executed before the next complete_command is tokenized and parsed, syntax errors are not discovered by the shell until just before the code would be executed. While in some cases it might be desirable to detect and react to syntax errors before anything is executed, deferring the discovery of syntax errors has several benefits:

• It makes it possible for script authors to test for the avilability of a nonstandard extension and react appropriately before the use of the extension would trigger a syntax error.
• It makes it possible to create self-extracting tarballs (a shell script concatenated with a payload archive that extracts the archive when executed).
• The shell does not have to read and parse the complete script before execution, which reduces memory usage when executing extremely long scripts.

However, unlike dot scripts, no PATH searching is performed. This is used as a guard against Trojan Horse security breaches.

However, unlike dot scripts, ENV scripts are parsed as a program, not a compound_list. This distinction matters because it influences when aliases take effect and whether syntax errors in the script are discovered before any part of the script is executed.

For security reasons, PATH is not searched when locating the ENV script.

Once a complete_command symbol has been recognized by the grammar (see [xref to 2.10 Shell Grammar]), the complete_command shall be subjected to alias substitution (see [xref to 2.3.1 Alias Substitution]) then executed before the next complete_command is tokenized and parsed.

After a token has been delimited, but before applying the grammatical rules in Section 2.10, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

After a sequeunce of tokens has been parsed and recognized as a command or compound list by the grammar (see [xref to 2.10 Shell Grammar]), but before the command or compound list is executed, each word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

After backslashes have been processed, the characters in command shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed.

The characters in command shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed.

This variable, when and only when an interactive shell is invoked, shall be subjected to parameter expansion (see Section 2.6.2) by the shell and the resulting value shall be used as a pathname of a file containing shell commands to execute in the current environment.

This variable, when and only when an interactive shell is invoked, shall be subjected to parameter expansion (see Section 2.6.2) by the shell and the resulting value shall be used as a pathname of a file. Before any interactive commands are read, the contents of the file shall be tokenized, parsed, subjected to alias expansion, and executed as described in [xref to 2.3 Token Recognition]. The contents shall be executed in the current environment.

The shell shall execute commands from the file in the current environment.

The contents of file shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed in the current environment.

The constructed command shall be read and executed by the shell.

The constructed command shall be tokenized (see [xref to XCU 2.3 Token Recognition]), then parsed as a single compound_list (see [xref to XCU 2.10 Shell Grammar]), then subjected to alias substitution (see [xref to 2.3.1]), then executed in the current environment.

/* The start symbol is compound_list when parsing dot scripts, command
   substitution bodies, and the arguments passed to eval */

Because a complete_command is executed before the next complete_command is tokenized and parsed, syntax errors are not discovered by the shell until just before the code would be executed. While in some cases it might be desirable to detect and react to syntax errors before anything is executed, deferring the discovery of syntax errors has several benefits:

• It makes it possible for script authors to test for the avilability of a nonstandard extension and react appropriately before the use of the extension would trigger a syntax error.
• It makes it possible to create self-extracting tarballs (a shell script concatenated with a payload archive that extracts the archive when executed).
• The shell does not have to read and parse the complete script before execution, which reduces memory usage when executing extremely long scripts.

However, unlike dot scripts, no PATH searching is performed. This is used as a guard against Trojan Horse security breaches.

However, unlike dot scripts, ENV scripts are parsed as a program, not a compound_list. This distinction matters because it influences when aliases take effect and whether syntax errors in the script are discovered before any part of the script is executed.

For security reasons, PATH is not searched when locating the ENV script.

In situations where the shell parses its input as a program, once a complete_command has been recognized by the grammar (see [xref to 2.10 Shell Grammar]), the complete_command shall be executed before the next complete_command is tokenized and parsed.

Use of <tt>set -n</tt> causes the shell to parse the rest of the script without executing any commands, meaning that <tt>set +n</tt> cannot be used to undo the effect. Syntax checking is more commonly done via <tt>sh -n script_name</tt>.

<tt>sh -n</tt> can be used to check for many syntax errors without waiting for complete_commands to be executed, but may be fooled into declaring false positives or missing actual errors that would occur when the shell actually evaluates eval commands present in the script, or if there are alias (or unalias) commands in the script that would alter the syntax of commands that use the affected aliases.

Because a complete_command encountered during a program is executed before the next complete_command is tokenized and parsed, syntax errors are not discovered by the shell until just before the code would be executed. While in some cases it might be desirable to detect and react to syntax errors before anything is executed (possible with <tt>sh -n</tt>), deferring the discovery of syntax errors has several benefits:

• It makes it possible for script authors to test for the availability of a nonstandard extension and react appropriately before the use of the extension would trigger a syntax error.


• It makes it possible to create self-extracting tarballs (a shell script concatenated with a payload archive that extracts the archive when executed).


• The shell does not have to read and parse the complete script before execution, which reduces memory usage when executing extremely long scripts.