Machine: x86_64 OS: linux-gnu Compiler: gcc Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-unknown-linux-gnu' -DCONF_VENDOR='unknown' -DLOCALEDIR='/usr/local/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H -I. -I. -I./include -I./lib -g -O2 -Wno-parentheses -Wno-format-security uname output: Linux DevVM 3.10.0-123.20.1.el7.x86_64 #1 SMP Thu Jan 29 18:05:33 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux Machine Type: x86_64-unknown-linux-gnu
Bash Version: 4.4 Patch Level: 0 Release Status: release Description: The behavior of arithmetic context operator $((..)) inside [[..]] is not so well defined. The GNU bash documentation says that $((..)) is not one of the valid primaries supported inside [[..]]. The downside is the operator without $ when used as ((..)) just behaves as double grouping, but $((..)) behaves as a valid arithmetic evaluation followed by non empty string comparison `-n` Steps The first snippet produces incorrect results because of lexicographic comparison of the two operands, while the second does an actual arithmetic evaluation which is NOT DOCUMENTED but in the end does a string not empty check with (-n 0) of the arithmetic evaluation result (not the exit code). This behavior needs to be explained clearly or documented well. bash -cx '[[ (( 100 < 3 )) ]] && echo ok' + bash -cx '[[ (( 100 < 3 )) ]] && echo ok' + [[ 100 < 3 ]] + echo ok bash -cx '[[ $(( 100 < 3 )) ]] && echo ok' + bash -cx '[[ $(( 100 < 3 )) ]] && echo ok' + [[ -n 0 ]] + echo ok ok bash -cx '[[ $(( 100 < 300 )) ]] && echo ok' + bash -cx '[[ $(( 100 < 300 )) ]] && echo ok' + [[ -n 1 ]] + echo ok ok -- Regards, INIAN VASANTH P
