Export the Bazelisk API once it is found. Subsequent calls cannot always

see the runfiles for bazel_binary.

bazel_integration_test/private/bazel_binaries_script.template

@@ -1,4 +1,5 @@
 #!/bin/bash
+# vi: ft=sh
 
 # --- begin runfiles.bash initialization v2 ---
 # Copy-pasted from the Bazel Bash runfiles library v2.
@@ -8,16 +9,21 @@ source "${RUNFILES_DIR:-/dev/null}/$f" 2>/dev/null || \
   source "$0.runfiles/$f" 2>/dev/null || \
   source "$(grep -sm1 "^$f " "$0.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
   source "$(grep -sm1 "^$f " "$0.exe.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
-  { echo>&2 "ERROR: cannot find $f"; exit 1; }; f=; set -e
+  { echo>&2 "ERROR: ${BASH_SOURCE[0]} cannot find $f"; exit 1; }; f=; set -e
 # --- end runfiles.bash initialization v2 ---
 
 export USE_BAZEL_VERSION="{version}"
 
-# Need to write data here, the default is read-obly inside tests.
-export BAZELISK_HOME="${PWD}"
+# Need to write data here, the default is read-only inside tests.
+if [[ -z "${BAZELISK_HOME:-}" ]]; then
+  export BAZELISK_HOME="${PWD}"
+fi
 
-# Find the bazelisk binary.
-BINARY="$(rlocation {bazelisk})" || \
-  (echo >&2 "Failed to locate bazelisk at {bazelisk}" && exit 1)
+# Find the bazelisk binary, if it has not already been found.
+if [[ -z "${BAZELISK_BINARY:-}" ]]; then
+  BAZELISK_BINARY="$(rlocation {bazelisk})" || \
+    (echo >&2 "Failed to locate bazelisk at {bazelisk}" && exit 1)
+  export BAZELISK_BINARY
+fi
 
-exec "${BINARY}" ${BIT_STARTUP_OPTIONS:-} "$@"
+exec "${BAZELISK_BINARY}" ${BIT_STARTUP_OPTIONS:-} "$@"