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Diffstat (limited to 'Documentation/CodingGuidelines')
| -rw-r--r-- | Documentation/CodingGuidelines | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines index 1d92b2da03..52afb2725f 100644 --- a/Documentation/CodingGuidelines +++ b/Documentation/CodingGuidelines @@ -204,6 +204,33 @@ For shell scripts specifically (not exhaustive): local variable="$value" local variable="$(command args)" + - The common construct + + VAR=VAL command args + + to temporarily set and export environment variable VAR only while + "command args" is running is handy, but this triggers an + unspecified behaviour according to POSIX when used for a command + that is not an external command (like shell functions). Indeed, + dash 0.5.10.2-6 on Ubuntu 20.04, /bin/sh on FreeBSD 13, and AT&T + ksh all make a temporary assignment without exporting the variable, + in such a case. As it does not work portably across shells, do not + use this syntax for shell functions. A common workaround is to do + an explicit export in a subshell, like so: + + (incorrect) + VAR=VAL func args + + (correct) + ( + VAR=VAL && + export VAR && + func args + ) + + but be careful that the effect "func" makes to the variables in the + current shell will be lost across the subshell boundary. + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g. "\xc2\xa2") in printf format strings, since hexadecimal escape sequences are not portable. |