5.2.2 Conditional expressions

Numeric value comparisons, character string comparisons, file attributes, logical operators, and ternary operators are used in conditional expressions. The following explains the specifications common to all conditional expressions.

The test or let command is used to evaluate conditions.

The test command includes the [[]] substitution format. The let command includes the (()) substitution format.
When you use the test command to evaluate conditions, insert a space between a variable and an operator. When you use [[]] instead of the test command, insert a space immediately after [[ and immediately before ]].

The following shows an example of a conditional using [[]].
```
if [[ $arg1 -eq $args ]]; then
    echo TRUE
fi
```
If an argument of the test command (such as -eq) is specified as an argument of the let command, the let command interprets that argument of the test command as a variable.

Organization of this subsection

(1) Numeric value comparison
(2) Character string comparison
(3) File attributes
(4) Logical operations
(5) Ternary operator

(1) Numeric value comparison

The following table lists and describes the operators used for comparing numeric values.

Table 5‒21: Operators used for comparing numeric values
Conditional expression using an operator	Evaluation	Usage in test command or [[]]	Usage in let command or (())
`numeric-value-1` `-eq` `numeric-value-2`	True if `numeric-value-1` is equal to `numeric-value-2`	Y	N
`numeric-value-1` `-ne` `numeric-value-2`	True if `numeric-value-1` is not equal to `numeric-value-2`	Y	N
`numeric-value-1` `-ge` `numeric-value-2`	True if `numeric-value-1` is equal to or greater than `numeric-value-2`	Y	N
`numeric-value-1` `-gt` `numeric-value-2`	True if `numeric-value-1` is greater than `numeric-value-2`	Y	N
`numeric-value-1` `-le` `numeric-value-2`	True if `numeric-value-1` is equal to or less than `numeric-value-2`	Y	N
`numeric-value-1` `-lt` `numeric-value-2`	True if `numeric-value-1` is less than `numeric-value-2`	Y	N
`numeric-value-1` `==` `numeric-value-2`	True if `numeric-value-1` is equal to `numeric-value-2`	Y^#1	Y
`numeric-value-1` `!=` `numeric-value-2`	True if `numeric-value-1` is not equal to `numeric-value-2`	Y^#1	Y
`numeric-value-1` `>=` `numeric-value-2`	True if `numeric-value-1` is equal to or greater than `numeric-value-2`	N	Y
`numeric-value-1` `>` `numeric-value-2`	True if `numeric-value-1` is greater than `numeric-value-2`	Y^{#1, #2}	Y
`numeric-value-1` `<` `numeric-value-2`	True if `numeric-value-1` is less than `numeric-value-2`	Y^{#1, #2}	Y
`numeric-value-1` `<=` `numeric-value-2`	True if `numeric-value-1` is equal to or less than `numeric-value-2`	N	Y

Legend:

Y: Permitted

N: Not permitted

#1

Compared as character strings, not numeric values. For details about character string comparison, see 5.2.2(2) Character string comparison.

#2

Can be used only in [[]]; cannot be used in any other format.

The following shows an example of numeric value comparison.

a=1
b=2
if [[ $a -lt $b ]]; then
  echo TRUE
else
  echo FALSE
fi
 
while (( $a != $b )); do
  echo LOOP
  ((a+=1))
done

To Page Top

(2) Character string comparison

The following table lists and describes the operators used for comparing character strings.

Table 5‒22: Operators used for comparing character strings
Conditional expression using an operator	Evaluation	Usage in test command or [[]]	Usage in let command or (())
`character-string`	True if the length of `character-string` is one or more characters. This operator cannot be used in `[[` `]]` commands.	Y	N
`-n` `character-string`	True if the length of `character-string` is one or more characters. If the length of `character-string` is `0`, the command outputs the `KNAX6041-E` message and terminates with an error with return code `2`. If no `character-string` is specified in the `[[` `]]` command, a format error results, in which case the command outputs the `KNAX6041-E` message and terminates with an error with return code `1`.	Y	N
`-z` `character-string`	True if the length of `character-string` is zero	Y	N
`-o` `character-string`	True if `character-string` matches the character string of the shell option that is currently valid. For details about the character string of the shell option, see Name in Table 5-34 Shell options that can be specified with the set command in 5.6.1 Shell options that can be specified with the set command.	Y	N
`character-string` `= pattern`	True if `character-string` matches `pattern`.	Y	N
`character-string` `== pattern`	True if `character-string` matches `pattern`.	Y	N
`character-string` `!= pattern`	True if `character-string` does not match `pattern`.	Y	N
`character-string-1` `<` `character-string-2`	`character-string-1` and `character-string-2` are compared in the order of ASCII codes. If `character-string-1` is less than `character-string-2`, the result is true.	Y^#	N
`character-string-1` `>` `character-string-2`	`character-string-1` and `character-string-2` are compared in the order of ASCII codes. If `character-string-1` is greater than `character-string-2`, the result is true.	Y^#	N

Legend:

Y: Permitted.

N: Not permitted.

#

Can be used only in [[]]; cannot be used in any other format.

Because any character string to be compared might contain one or more spaces, we recommend that you always enclose the entire character string in double quotation marks ("). The following shows examples.

str1="aaa"
str2="bbb"
test "$str1" == "$str2"
[[ "$str1" == "$str2" ]]

You can specify the *, ?, and [...] wildcard characters in character strings to be compared. Note that wildcards can be specified only in [[ ]], not in any other format. Note that when a character string containing a wildcard character is enclosed in double quotation marks ("), the use of the wildcard character as a wildcard character becomes invalid. The following shows an example.

str1="adsh"
str2="ads?"
str3="ad*"
[[ "$str1" == "$str2" ]]    The wildcard character is invalid. The character string "ads?" is compared.
[[ $str1 != $str3 ]]        The wildcard character is valid.

The following shows an example of character string comparison using [[]]. The *, ?, and [...]wildcard characters can be used.

if [[ abc == ab* ]]; then
    echo TRUE
fi

For details about wildcard characters, see 5.1.6(5) Wildcards.

To Page Top

(3) File attributes

The following table lists and describes the operators used for evaluating file attributes, such as file formats and permissions.

Table 5‒23: Operators used for evaluating file attributes, such as file formats and permissions
Conditional expression using an operator	Evaluation	Usage in test command or [[]]	Usage in let command or (())
`-a` `file`	True if `file` exists.	Y	N
`-b` `file`	True if `file` exists and it is a block type device.^#1	Y	N
`-c` `file`	True if `file` exists and it is a character type device.^#1	Y	N
`-d` `file`	True if `file` exists and it is a directory.	Y	N
`-e` `file`	True if `file` exists.	Y	N
`-f` `file`	True if `file` exists and it is a regular file.	Y	N
`-g` `file`	True if `file` exists and the `setgid` bit is set.^#1	Y	N
`-h` `file`	True if `file` exists and it is a symbolic link.^#2	Y	N
`-k` `file`	True if `file` exists and a sticky bit is set.^#1	Y	N
`-p` `file`	True if `file` exists and it is a pipe file.^#1	Y	N
`-r` `file`	In Windows, the result is true if `file` exists; in UNIX, the result is true if `file` exists and it can be read from the current process.	Y	N
`-s` `file`	True if the following conditions are all satisfied: In Windows: `file` exists. `file` is not a folder. The file size is at least 1 byte. In UNIX: `file` exists. The file size is at least 1 byte or `file` is a directory. With `-s`, because the conditions for `true` differ between UNIX and Windows, use `-d` to check if `file` is a directory or folder.	Y	N
`-t fd`	True if this is `fd` whose terminal is open.^#3	Y	N
`-u` `file`	True if `file` exists and the `setuid` bit is set.^#1	Y	N
`-w` `file`	In Windows, the result is true if the read-only attribute is not set or this is a directory; in UNIX, the result is true if `file` exists and it can be written from the current process.	Y	N
`-x` `file`	In Windows, the result is true if one of the following is true: The extension is `.com`, `.exe`, `.cmd`, or `.bat`. This is a directory. The file satisfies the condition specified in the `CHILDJOB_EXT` or `CHILDJOB_SHEBANG` parameter (including a default definition) in the environment file.^#4 In UNIX, the result is true if `file` exists and it can be executed from the current process.	Y	N
`-G` `file`	True if `file` exists and the group to which `file` belongs matches the ID of the group executing the calling process.^#2	Y	N
`-L` `file`	True if `file` exists and it is a symbolic link.^#2	Y	N
`-O` `file`	True if `file` exists and its owner has a valid user ID for the process.^#2	Y	N
`-S` `file`	True if `file` exists and it is a socket.^#1	Y	N
`file1 -ef` `file2`	True if `file1` and `file2` exist and the entities of `file1` and `file2` are the same (if either their symbolic link or hard link targets are the same).^#2	Y	N
`file1` `-nt` `file2`	True if `file1` and `file2` exist and the most recent modification date and time of `file1` is more recent than the most recent modification date and time of `file2`; also true if `file1` exists and `file2` does not exist.	Y	N
`file1` `-ot` `file2`	True if `file1` and `file2` exist and the most recent modification date and time of `file1` is earlier than the most recent modification date and time of `file2`; also true if `file2` exists and `file1` does not exist.	Y	N
`-H` `file`	Always false	Y	N

Legend:

Y: Permitted

N: Not permitted

#1

In a Windows environment, the result is always false because this check occurs on nonexistent file types and flags.

#2

If the test command is executed in a Windows environment, it always results in an error because the processing is not supported during evaluation. However, you can set it to issue a message and result in an error or to treat it as normal by specifying the UNSUPPORT_TEST parameter. For details about the parameter, see UNSUPPORT_TEST parameter (defines the handling of an unsupported conditional expression) (Windows only) in 7.3 Environment setting parameters.

#3

Do not specify a value greater than 9 in fd. If you do, the value cannot be guaranteed.

#4

For details about the CHILDJOB_SHEBANG parameter, see CHILDJOB_SHEBANG parameter (defines an executable program path for job definition script files that are to be executed as child jobs) in 7.3 Environment setting parameters.

For details about the CHILDJOB_EXT parameter, see CHILDJOB_EXT parameter (defines an extension for job definition script files that are to be executed as child jobs) in 7.3 Environment setting parameters.

The following shows an example of evaluating a file attribute.

FILE="$HOME/script/test.ash"
if [[ -a $FILE ]];
then
  echo "$FILE exists."
else
  echo "$FILE does not exist."
fi

To Page Top

(4) Logical operations

The following table lists and describes the operators used for evaluation in logical operations.

Table 5‒24: Operators used for evaluation in logical operations
Conditional expression using an operator	Evaluation	Usage in test command or [[]]	Usage in let command or (())
`expr1` `-a` `expr2`	True if the results of `expr1` and `expr2` are both true	Y^#	N
`expr1` `-o` `expr2`	True if the result of either `expr1` or `expr2` is true	Y^#	N
`expr1` `&&` `expr2`	True if the results of `expr1` and `expr2` are both true	Y	Y
`expr1` `\|\|` `expr2`	True if the result of either `expr1` or `expr2` is true	Y	Y
`!` `expr`	True if the result of `expr` is false	Y	Y

Legend:

Y: Permitted

N: Not permitted

#

Cannot be used in [[]].

The following shows an example of a logical operation.

DIR="/tmp"
FILE="/tmp/test.ash"
a=2
b=4
if test -d $DIR -a -a $FILE
then
  echo "$DIR is directory and $FILE exists."
else
  echo "$DIR is not directory or $FILE does not exist."
fi
 
while ((a*0 || b-3)); do
  echo LOOP
  let b-=1
done

If you use && and || in the test command, specify them as follows:

a=1
b=2
c=3
if test "$a" == 1 && test "$b" == 2; then
    echo "True"
else
    echo "False"
fi
if test "$a" != "$b" || test "$a" != "$c"; then
    echo "True"
else
    echo "False"
fi

To Page Top

(5) Ternary operator

You can use the ternary operator, which is an abbreviated notation of if-else. The following table explains the ternary operator supported by JP1/Advanced Shell.

Table 5‒25: Ternary operator supported by JP1/Advanced Shell
Conditional expression using an operator	Evaluation	Usage in test command or [[]]	Usage in let command or (())
`expr1?expr2:` `expr3`	If the result of `expr1` is true, the result of `expr2` is returned. If the result of `expr1` is false, the result of `expr3` is returned.	N	Y

Legend:

Y: Permitted

N: Not permitted

The following shows an example of the ternary operator.

VAR1=3
VAR2=2
ANSWER=0
 
((ANSWER=VAR1>VAR2?8+VAR1:8*VAR2))
echo $ANSWER

To Page Top