On 8/12/16 4:52 AM, NO REPLY wrote:
> Bash Version: 4.3
> Patch Level: 11
> Release Status: release
>
> Description:
> I have a few increment expressions used as ((level++)) and only one of
> those is giving an error. When used with set -e, bash aborts
> execution. Using ERR trap, I was able to identify the expression.
>
>
> Repeat-By:
>
> I have this simple logic in which I am running a sequence of commands
> conditionally, based on what a user provided level is.
> The intention is to only run those groups of commands appropriate for
> the level specified. To demonstrate the idea, here is
> a simple script:
>
> >>> CUT HERE <<<
> #!/usr/bin/env bash
> set -eEu -o pipefail
>
> trap 'echo "*** ERROR: Detected error on command: $BASH_COMMAND at
> line: $LINENO"' ERR
>
> DEBUG_LEVEL=$1
>
> function debug_mode() {
> declare -i level=0
> (( level >= DEBUG_LEVEL )) || {
> echo "Running: level $((level+1)) commands"
> ((level++))
> }
> (( level >= DEBUG_LEVEL )) || {
> echo "Running: level $((level+1)) commands"
> ((level++))
> }
> }
>
> debug_mode
> >>> CUT HERE <<<
>
> When this script works (as is the case on "GNU bash, version
> 3.2.57(1)-release (x86_64-apple-darwin15)"), you would see the below
> interaction:
>
> $ debug.sh 0
> $ debug.sh 1
> Running level 1 commands
> $ debug.sh 2
> Running level 1 commands
> Running level 2 commands
>
> However, when run on this version of bash (or even on GNU bash, version
> 4.1.2(1)-release (x86_64-redhat-linux-gnu)), the first "((level++))" results
> in an error:
>
> $ debug.sh 0
> $ debug.sh 1
> Running: level 1 commands
> *** ERROR: Detected error on command: ((level++)) at line: 8
>
> If I replace the first "((level++))" with ": $((level++))" or
> "level+=1", then it goes through fine, and the second "((level++))" doesn't
> generate any error.
The relevant change was probably the change in the set of commands to which
`set -e' applies. The (( command (among others) was added to that list
in bash-4.1. The change was the result of Posix changing the semantics
of the errexit option and expanding its scope from simple commands to
all commands.
The (( command returns 1 if the expression evaluates to 0. When `level' is
0, level++ returns a 0 value, and (( returns a status of 1.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
