5.1.6 Metacharacters

(a) Variable substitution

Variable substitution includes substitution of a variable based on the status of the variable, substitution of a variable for the length of a character string constituting the value of a variable or for the number of elements in an array, substitution of a variable based on the result of pattern matching, and substring expansion.

• Variable substitution depending on the status of the variable

  The table below lists and describes the formats used to perform variable substitution depending on the status of the variable. In these formats, variable represents a variable name and word represents the variable that is expanded according to the status of variable. In the examples and results, a indicates an undefined variable, b=NULL, and c=1.

  Table 5‒9: Formats used to perform variable substitution depending on the status of the variable

  Format	Description	Examples	Results
  ${variable:-word}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If variable is defined but its value is NULL or undefined, the expansion result of word is returned. The value of variable remains unchanged.	cnt=${a:-7}	7 is assigned to cnt.
  		cnt=${b:-8}	8 is assigned to cnt.
  		cnt=${c:-9}	Value of c is assigned to cnt.
  ${variable-word}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If variable is defined and its value is NULL, the value of variable (NULL) is returned. If variable is undefined, the expansion result of word is returned. The value of variable remains unchanged.	cnt=${a-7}	7 is assigned to cnt.
  		cnt=${b-8}	NULL is assigned to cnt.
  		cnt=${c-9}	Value of c is assigned to cnt.
  ${variable:=word}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If variable is defined and its value is NULL or undefined, the expansion result of word is assigned to variable, and then the value of variable is returned. Note that this format is applicable only to variables, not to positional parameters.	cnt=${a:=7}	7 is assigned to a and the value of a is assigned to cnt.
  		cnt=${b:=8}	8 is assigned to b and the value of b is assigned to cnt.
  		cnt=${c:=9}	Value of c is assigned to cnt.
  ${variable=word}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If variable is defined and its value is NULL, the value of variable (NULL) is returned. If variable is undefined, the expansion result of word is assigned to variable, and then the value of variable is returned. Note that this format is applicable only to variables, not to positional parameters.	cnt=${a=7}	7 is assigned to cnt.
  		cnt=${b=8}	NULL is assigned to cnt.
  		cnt=${c=9}	Value of c is assigned to cnt.
  ${variable:?[word]}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If word is specified and variable is defined and its value is NULL or undefined, the expansion result of word is output to the standard error output, and then the job definition script is terminated. If word is omitted and variable is defined and its value is NULL or undefined, the KNAX6050-E message indicating that variable is undefined is issued, and then the job definition script is terminated. The value of variable remains unchanged.	cnt=${a:?7}	The expansion result is output to the standard error output, and then the shell is terminated.
  		cnt=${a:?}	A message is output, and then the shell is terminated.
  		cnt=${b:?8}	The expansion result is output to the standard error output, and then the shell is terminated.
  		cnt=${c:?9}	Value of c is assigned to cnt.
  ${variable?[word]}	If variable is defined as a variable and a value is assigned to it, the value of variable is returned. If word is specified and variable is undefined, the expansion result of word is output to the standard error output, and then the job definition script is terminated. If word is omitted and variable is undefined, the KNAX6050-E message indicating that variable is undefined is issued, and then the job definition script is terminated. The value of variable remains unchanged.	cnt=${a?7}	The expansion result is output to the standard error output, and then the shell is terminated.
  		cnt=${a?}	A message is output, and then the shell is terminated.
  		cnt=${b?8}	NULL is assigned to cnt
  		cnt=${c?9}	Value of c is assigned to cnt. Value of c is assigned to cnt.
  ${variable:+word}	If variable is defined as a variable and a value is assigned to it, the expansion result of word is returned. Otherwise, NULL is returned. The value of variable remains unchanged.	cnt=${a:+7}	NULL is assigned to cnt.
  		cnt=${b:+8}	NULL is assigned to cnt.
  		cnt=${c:+9}	9 is assigned to cnt.
  ${variable+word}	If variable is defined as a variable and a value is assigned to it or the value is NULL, the expansion result of word is returned. Otherwise, NULL is returned. The value of variable remains unchanged.	cnt=${a+7}	NULL is assigned to cnt.
  		cnt=${b+8}	8 is assigned to cnt.
  		cnt=${c+9}	9 is assigned to cnt.

• Variable substitution to the length of the character string constituting the value of the variable or to the number of array elements

  The table below lists and describes the formats used to perform variable substitution to the length of the character string constituting the value of the variable or to the number of array elements. In these formats, variable represents a variable name and array represents an array name.

  Table 5‒10: Formats used to perform variable substitution to the length of the character string constituting the value of the variable or to the number of array elements

  Format	Description
  ${#variable}	If variable is * or @, the variable is replaced with the number of positional parameters. Otherwise, the variable is replaced according to the setting specified for the VAR_SHELL_GETLENGTH environment setting parameter: BYTE Replaces the length of the value stored in variable with the number of bytes. CHARACTER Replaces the length of the value stored in variable with the number of characters. If the VAR_SHELL_GETLENGTH environment setting parameter is not specified, the operation is the same as when BYTE is specified in the VAR_SHELL_GETLENGTH environment setting parameter.
  ${#array[*]}	The value is replaced with the number of elements of the array specified by array.
  ${#array[@]}

• Variable substitution based on the result of pattern matching

  The table below lists and describes the formats used to perform variable substitution based on the result of pattern matching. In these formats, variable represents a variable name and pattern represents a character string used to perform pattern matching with variable. Wildcard characters can be used in pattern.

  Table 5‒11: Formats used to perform variable substitution based on the result of pattern matching

  Classification	Format	Description
  Leading match	${variable#pattern }	If pattern matches the leading part of the variable value, the value in variable is replaced with its value less the shortest matching part (the shortest-matching part is deleted). Otherwise, the variable is replaced with the value of variable.
  	${variable##pattern }	If pattern matches the leading part of the variable value, the variable is replaced with its value less the longest matching part (the longest-matching part is deleted). Otherwise, the variable is replaced with the value of variable.
  Trailing match	${variable%pattern }	If pattern matches the trailing part of the variable value, the variable is replaced with its value less the shortest matching part (the shortest-matching part is deleted). Otherwise, the variable is replaced with the value of variable.
  	${variable%%pattern }	If pattern matches the trailing part of the variable value, the variable is replaced with its value less the longest matching part (the longest-matching part is deleted). Otherwise, the variable is replaced with the value of variable.

  The following shows an example of outputting a variable value with deletion of a specified character string (leading match).

  Contents of the job definition script:

  abc=abcd1234xyz987abcd1234efg
  echo ${abc#abcd}         # 1.
  echo ${abc#a*2}          # 2.
  echo ${abc##a*2}         # 3.
  echo ${abc#*1234}        # 4.
  echo ${abc##*1234}       # 5.
  echo ${abc#1234}         # 6.

  STDOUT file contents of the executed job:

  ********   JOB SCOPE STDOUT    ********
  1234xyz987abcd1234efg       Result of 1: The leading character string abcd is deleted.
  34xyz987abcd1234efg         Result of 2: The string of characters from a through 2 is deleted (shortest match).
  34efg                       Result of 3: The string of characters from a through 2 is deleted (longest match).
  xyz987abcd1234efg           Result of 4: The string of characters from the beginning through 1234 is deleted (shortest match).
  efg                         Result of 5: The string of characters from the beginning through 1234 is deleted (longest match).
  abcd1234xyz987abcd1234efg   Result of 6:The value of abc is output because there is no leading match.

  The following shows an example of outputting a variable value with deletion of a specified character string (trailing match).

  Contents of the job definition script:

  abc=abcd1234xyz987abcd1234
  echo ${abc%1234}         # 1.
  echo ${abc%d*4}          # 2.
  echo ${abc%%d*4}         # 3.
  echo ${abc%34*}          # 4.
  echo ${abc%%34*}         # 5.
  echo ${abc%abcd}         # 6.

  STDOUT file contents of the executed job:

  ********   JOB SCOPE STDOUT    ********
  abcd1234xyz987abcd      Result of 1: The trailing character string 1234 is deleted.
  abcd1234xyz987abc       Result of 2: The trailing character string from d through 4 is deleted (shortest match).
  abc                     Result of 3: The trailing character string from d through 4 is deleted (longest match).
  abcd1234xyz987abcd12    Result of 4: The character string beginning with 34 is deleted (shortest match).
  abcd12                  Result of 5: The character string beginning with 34 is deleted (longest match).
  abcd1234xyz987abcd1234  Result of 6: The value of abc is output because there is no trailing match.

• Substring expansion

  The following table lists and describes the formats for variable substitution that is performed based on the result of substring expansion.

  Table 5‒12: Formats for substring expansion

  Format	Description
  ${variable:offset}	Retrieves characters from the expansion result of variable. offset specifies the start position of the characters to be retrieved.
  ${variable:offset:length}	Retrieves as many characters as there are in maximum length from the expansion result of variable. offset specifies the start position of the characters to be retrieved.
  ${array[*]:offset}	Retrieves elements that begin with ${array[offset]} of the array.
  ${array[*]:offset:length}	Retrieves as many elements as there are in length that begin with ${array[offset]} of the array.
  ${array[@]:offset}	Retrieves elements that begin with ${array[offset]} of the array.
  ${array[@]:offset:length}	Retrieves as many elements as there are in length that begin with ${array[offset]} of the array.

  Legend:

  variable: Specifies a variable name.

  array: Specifies an array name.

  offset: Specifies the start position in the character string or array element subject to partial expansion.

  length: Specifies the number of characters or array elements to be expanded.

(b) Command substitution

The table below lists and describes the formats used to perform command substitution. In these formats, command represents the name of the command and the arguments to be executed.

In Windows, command substitution is performed in the current process except for external commands.

In the grave character format, a backslash (\) in the character string of command is treated as a metacharacter. Therefore, if the character string of command contains \, the execution results differ between the $( ) and the grave character formats. We recommend that you use the $( ) format.

The following shows example specifications and execution results.

• $( ) format

  Specification example:

  echo $(echo '\$x')

  Execution result:

  \$x

• Grave character format

  Specification example:

  echo `echo '\$x'`

  Execution result:

  $x

(c) File name substitution

The table below lists and describes the formats used to perform file name substitution. In these formats, pattern represents a character string used for pattern matching. Wildcard characters can be used in pattern.

You can replace file names by specifying multiple patterns delimited by the vertical bar (|). Do not specify any spaces before or after the vertical bar delimiter. If there is such a space, it will be regarded as part of the pattern.

The following shows examples.

Example of file name substitution

Contents of job definition script:

ls -C                     # 1. Display the file in the current directory
ls -C ?(*.sh|*.exe|*.dot) # 2. Display the file names whose extension is sh,exec, or dot
ls -C *(*.sh|*.exe)       # 3. Display the file names whose extension is either sh or exe
ls -C +(*.jhs|*h)         # 4. Display the file names whose extension is jhs or that end with h
ls -C @(*.c|*.jhs)        # 5. Display the file names whose extension is c or jhs
ls -C !(*.c|*.jhs)        # 6. Display the file names whose extension is neither c nor jhs

STDOUT file contents of the executed job:

********   JOB SCOPE STDOUT    ********
a.jhs  a.sh   a.txt  func.c   Execution result of 1
a.sh                          Execution result of 2
a.sh                          Execution result of 3
a.jhs a.sh                    Execution result of 4
a.jhs  func.c                 Execution result of 5
a.sh  a.txt                   Execution result of 6

File names beginning with a dot (.) are excluded as targets of pattern matching. To include file names beginning with a dot as targets of pattern matching, you must specify the dot explicitly.

(a) Redirection

The table below describes the redirection methods supported by JP1/Advanced Shell. A redirection is interpreted from left to right.

(b) File descriptors

The following table lists and describes the file descriptors in JP1/Advanced Shell by type of input and output.

(c) Here document

A here document refers to creation of the standard input within the job definition script. The following table lists and describes the formats related to here documents.

(d) Pipes

When you want to connect multiple commands and use the standard output from one command as the standard input to another, you can use pipes to connect the commands. A set of commands connected by a pipe is called a pipeline.

• In Windows

  A pipeline is processed from left to right, and the commands in a pipeline are executed sequentially. Among built-in commands, functions, and external commands, only the external commands are executed as separate processes. Temporary files are used to transfer data between commands.

• In UNIX

  A pipeline is processed from left to right, and the commands in a pipeline are executed as separate processes.

  You can use the PIPE_CMD_LAST parameter to define whether the last command is to be executed in the current process or in a separate process. The default is the current process.^#

  For details about the PIPE_CMD_LAST parameter, see PIPE_CMD_LAST parameter (defines execution processing for the last command in a pipe) (UNIX only) in 7. Parameters Specified in the Environment Files.

  #

  This is not applicable to commands executed in separate processes (such as external commands, child jobs, UNIX-compatible commands, shell operation commands, subshells, commands with a background specified, and commands with a background process specified).

  Also in UNIX, if multiple commands are connected by a pipe and then the output command outputs data to the pipe after the input command has terminated and while there is no process, the output command might receive SIGPIPE.

  In JP1/Advanced Shell, the command issues the KNAX6522-E message and terminates with an error unless the command handles SIGPIPE.