3 SC2084

Joachim Ansorg edited this page 2021-11-12 19:29:43 +01:00

Table of Contents

• Remove $ or use _=$((expr)) to avoid executing output.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:

Remove $ or use _=$((expr)) to avoid executing output.

Problematic code:

i=4
$(( i++ ))

Correct code:

Bash, Ksh:

i=4
(( i++ ))

POSIX (assuming ++ is supported):

i=4
_=$(( i++ ))

Alternative POSIX version that does not preserve the exit code:

: $(( i++ ))

Rationale:

$((..)) expands to a number. If it's the only word on the line, the shell will try to execute this number as a command name:

$ i=4
$ $(( i++ ))
4: command not found
$ echo $i
5

To avoid trying to execute the number as a command name, use one of the methods mentioned:

$ i=4
$ _=$(( i++ ))
$ echo $i
5

Exceptions:

None.

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