$ tail -f nix-env.out
installing ‘python-2.7.9’
these derivations will be built:
  /nix/store/3v5hknmci8mipwyrsnzp01imj034hzxj-binutils-2.23.1.drv
  /nix/store/38hkdqpn6llzcbi88bhz3524m7258ahd-bootstrap-gcc-wrapper.drv
  /nix/store/la97c4k0gykkvb1jsi4ffsb28k8g2wsy-stdenv-linux-boot.drv
  /nix/store/clzcvf528yzkw0cd0k9vixb1wnmqvl9f-patchelf-0.8.drv
  /nix/store/71i3cyw1y2h28chs7axs5f7n1ja7w29l-perl-5.20.1.drv
  /nix/store/bbp6fd1glbn13j9l80rxmf4pchnyciqb-linux-headers-3.12.32.drv
  /nix/store/fdv584xg1lsqgbfxwqhgn6rlf9b5f3xy-glibc-2.20.drv
  /nix/store/m7naxa3hdwv67sks87ld46pw0fg5gb2s-bootstrap-gcc-wrapper.drv
  /nix/store/lcca5kgs255f7xwcvsxa97lsg08025sp-stdenv-linux-boot.drv
  /nix/store/h771s6zvghwzbg4kw9c4xss3ix0ivgb4-xz-5.0.7.drv
  /nix/store/1pjjh2x4xpgmm1qxylvqkwi1ajwjrm24-libelf-0.8.13.drv
  /nix/store/cs1pr1x6zjb0lryzj64gzmi64ypmj223-gettext-0.18.2.drv
  /nix/store/qyxlwnl7xj6c811k9n2npwgndryqq8hl-gnum4-1.4.17.drv
  /nix/store/ibccvj7a601ljhacdlrhck5h6siwmwm8-gmp-5.1.3.drv
  /nix/store/d9ap3nm68mrippmidgplzij291mgxdrk-mpfr-3.1.2.drv
  /nix/store/giwhbqbr46191g3zq066ymcwhl032pai-isl-0.11.1.drv
  /nix/store/iz04yk30219yhxvc52ns7zyj7ib5yily-texinfo-5.2.drv
  /nix/store/lf3gwj9hpgyw8fy26mi85cnvqfy66xm6-zlib-1.2.8.drv
  /nix/store/p1na89862n1xw4rplj5wagk6kjz634hf-mpc-1.0.1.drv
  /nix/store/wfsz86d1jc8ncja5y57ydyp0jy0x2hva-cloog-0.18.0.drv
  /nix/store/zr7c9ajgjsrl2h3zvh4igyx5jqknl5yv-which-2.20.drv
  /nix/store/xlklhrw6lvsdks8643w69y8rnpwh8wa8-gcc-4.8.4.drv
  /nix/store/pfq1lbpd6da1329l1my2i1g0z35sg2f1-gcc-wrapper-4.8.4.drv
  /nix/store/0k87ff7pfnznp7mps1gm5fc2nsnhkqx0-stdenv-linux-boot.drv
  /nix/store/0i00xqf4k9cybqfm0dh3y8qc464z5av9-gnumake-3.82.drv
  /nix/store/xgaap7k8pgwcnji1dj2v64jkv46wnl5p-bison-3.0.2.drv
  /nix/store/2syabp461y6a71jxqw7q83g0bam8vc75-binutils-2.23.1.drv
  /nix/store/3803kf5y5rygm06i8nk62w848hjwk0yw-attr-2.4.47.drv
  /nix/store/4vldcm30f4w0d5hlr72lb5jf8xq2h2xd-pcre-8.36.drv
  /nix/store/6380f1ldlx04hvbb99fcgybvrfz5s2c1-bash-4.3-p30.drv
  /nix/store/9yszswvg75vyb1pzxhkibm2fgjbaszvy-acl-2.2.52.drv
  /nix/store/qvdvzr6rqasxirnnn3alhdmwxmnwkqag-coreutils-8.23.drv
  /nix/store/9izlmfajv21881zmn7q6fqi05aja4gqj-diffutils-3.3.drv
  /nix/store/9w1vzc2zdppfy1q774khps1xb9l5i7ry-findutils-4.4.2.drv
  /nix/store/a6bpp9z50cfkx598yvf8ps3p8vx2x7ig-paxctl-0.9.drv
  /nix/store/aayl5bydn6xyj8yh8l4h6kinwh9xbrgb-gnutar-1.27.1.drv
  /nix/store/cvacnn61zhqhmgs11gjm65pdzx6mqjzv-xz-5.0.7.drv
  /nix/store/fbj5hg7l2dzz27n83gk1938bbsc9bg7x-ed-1.10.drv
  /nix/store/fmbcqczjmmjhjszsfj1d039bv822g8rp-bzip2-1.0.6.drv
  /nix/store/i1f6s3lfz5vsrainkxbs28f7wx993js3-libsigsegv-2.10.drv
  /nix/store/i9jwjpir4sf2gcdvnynqj030ibij2d6q-gawk-4.1.0.drv
  /nix/store/pa0gyxslpvcbmjf53kzygk7jg1avzbj6-gnused-4.2.2.drv
  /nix/store/sqb2dd905xkvjsn78wxr1ksnsfs4m101-patch-2.7.1.drv
  /nix/store/vlflyjb3kz3gca1as1cbilxdw4bksafx-gnugrep-2.20.drv
  /nix/store/wc3y3xhbh0axfb4a18l1h311jgpayysp-gcc-wrapper-4.8.4.drv
  /nix/store/z19jf62lc8k5h98jwpkajzmlnfqai32m-patchelf-0.8.drv
  /nix/store/zz3rc5fpk3yg6d3nfmdkqmnyhy0nnc6m-gzip-1.6.drv
  /nix/store/9pv87rb81y58683z3a9sb0pabzgjfrzh-stdenv.drv
  /nix/store/9mwnbdwxx9jg9b9cali0kng7xc9pb29q-perl-5.20.1.drv
  /nix/store/yrxzvvmmkj56c24p7vdy0sh2mlv7h9gn-openssl-1.0.1k.drv
  /nix/store/r5iasm9rx8li81m2by9xj8a0jwfwp0sc-libssh2-1.4.3.drv
  /nix/store/ksbyfbvzlbxbbgqn73rpjhfnnq5z6b98-curl-7.39.0.drv
  /nix/store/pr7ixfsmrllmhjacy2ajjs66y8d324n4-mirrors-list.drv
  /nix/store/jzk9k3z91qbmdz0zbpfvqmc9zmzb6s9v-Python-2.7.9.tar.xz.drv
  /nix/store/ml8wam02r100rzvsjqk0306xf6r899q0-python-2.7.9.drv
building path(s) ‘/nix/store/srnm2pxxpiidqcj106i9i4avqvk7vx7k-perl-5.20.1’
building path(s) ‘/nix/store/vp1x4d7zscqjbkn81kcw13bnaxwcg3g5-binutils-2.23.1’
building /nix/store/srnm2pxxpiidqcj106i9i4avqvk7vx7k-perl-5.20.1
unpacking sources
building /nix/store/vp1x4d7zscqjbkn81kcw13bnaxwcg3g5-binutils-2.23.1
unpacking sources
unpacking source archive /nix/store/6wxzsh0m6gzvr398fm9wmshfbwsn819n-perl-5.20.1.tar.gz
unpacking source archive /nix/store/n69kz335c800n2b6izsjbw60rlnvp87c-binutils-2.23.1.tar.bz2
source root is perl-5.20.1
patching sources
applying patch /nix/store/x0i6f1q7if2v0gl0fk68kw3ak2fyhp1v-no-sys-dirs.patch
patching file Configure
patching file ext/Errno/Errno_pm.PL
patching file hints/freebsd.sh
patching file hints/linux.sh
configuring
configure flags: -de -Dcc=cc -Uinstallusrbinperl -Dinstallstyle=lib/perl5 -Duseshrplib -Dlocincpth=/nix/store/ymrknw7a6bfwin4gknaxvk2nqw2wq0vh-bootstrap-glibc/include -Dloclibpth=/nix/store/ymrknw7a6bfwin4gknaxvk2nqw2wq0vh-bootstrap-glibc/lib -Dprefix=/nix/store/srnm2pxxpiidqcj106i9i4avqvk7vx7k-perl-5.20.1 -Dman1dir=/nix/store/srnm2pxxpiidqcj106i9i4avqvk7vx7k-perl-5.20.1/share/man/man1 -Dman3dir=/nix/store/srnm2pxxpiidqcj106i9i4avqvk7vx7k-perl-5.20.1/share/man/man3

Beginning of configuration questions for perl5.

Checking echo to see how to suppress newlines...
...using -n.
The star should be here-->*

First let's make sure your kit is complete.  Checking...
Looks good...