composer requires php5 while php7 is installed on the system
$ docker run --rm -it alpine sh / # apk add --update --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing php7 composer fetch http://dl-cdn.alpinelinux.org/alpine/edge/testing/x86_64/APKINDEX.tar.gz fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz (1/14) Installing php5-common (5.6.24-r0) (2/14) Installing pcre (8.38-r1) (3/14) Installing ncurses-terminfo-base (6.0-r7) (4/14) Installing ncurses-terminfo (6.0-r7) (5/14) Installing ncurses-libs (6.0-r7) (6/14) Installing readline (6.3.008-r4) (7/14) Installing libxml2 (2.9.4-r0) (8/14) Installing php5-cli (5.6.24-r0) (9/14) Installing php5 (5.6.24-r0) (10/14) Installing php5-phar (5.6.24-r0) (11/14) Installing php5-json (5.6.24-r0) (12/14) Installing composer (1.2.0-r0) (13/14) Installing php7-common (7.0.10-r1) (14/14) Installing php7 (7.0.10-r1) Executing busybox-1.24.2-r8.trigger OK: 32 MiB in 25 packages
(from redmine: issue id 6069, created on 2016-08-20, closed on 2018-08-22)